Comparative study of six sequential spectrophotometric methods for quantification and separation of ribavirin, sofosbuvir and daclatasvir: An application on Laboratory prepared mixture, pharmaceutical preparations, spiked human urine, spiked human plasma, and dissolution test

In accordance with International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) guidelines, six novel, simple and precise sequential spectrophotometric methods were developed and validated for the simultaneous analysis of Ribavirin (RIB), Sofosbuvir (SOF), and Daclatasvir (DAC) in their mixture without prior separation steps. These drugs are described as co-administered for treatment of Hepatitis C virus (HCV). HCV is the cause of hepatitis C and some cancers such as liver cancer (hepatocellular carcinoma) and lymphomas in humans. These techniques consisted of several sequential steps using zero, ratio and/or derivative spectra. DAC was first determined through direct spectrophotometry at 313.7 nm without any interference of the other two drugs while RIB and SOF can be determined after ratio subtraction through five methods; Ratio difference spectrophotometric method, successive derivative ratio method, constant center, isoabsorptive method at 238.8 nm, and mean centering of the ratio spectra (MCR) at 224 nm and 258 nm for RIB and SOF, respectively. The calibration curve is linear over the concentration ranges of (6-42), (10-70) and (4-16) μg/mL for RIB, SOF, and DAC, respectively. This method was successfully applied to commercial pharmaceutical preparation of the drugs, spiked human urine, and spiked human plasma. The above methods are very simple methods that were developed for the simultaneous determination of binary and ternary mixtures and so enhance signal-to-noise ratio. The method has been successfully applied to the simultaneous analysis of RIB, SOF, and DAC in laboratory prepared mixtures. The obtained results are statistically compared with those obtained by the official or reported methods, showing no significant difference with respect to accuracy and precision at p = 0.05.

Population pharmacokinetics of paritaprevir, ombitasvir, dasabuvir, ritonavir and ribavirin in hepatitis C virus genotype 1 infection: analysis of six phase III trials

AIM

The aim of the current study was to characterize the population pharmacokinetics of a triple direct-acting antiviral (DAA) regimen (3D) (ombitasvir, paritaprevir-ritonavir and dasabuvir) and adjunctive ribavirin, and estimate covariate effects in a broad spectrum of subjects with hepatitis C virus (HCV) genotype 1 infection.

METHODS

Pharmacokinetic data from six phase III studies and one phase II study in subjects receiving the currently approved doses of the 3D ± ribavirin regimen for treating HCV genotype 1 infection for 12 weeks or 24 weeks were characterized using separate population pharmacokinetic models, built using each component of the regimen from nonlinear mixed-effects methodology in NONMEM 7.3. In the models, demographic and clinical covariates were tested. Models were assessed via goodness-of-fit plots, visual predictive checks and bootstrap evaluations.

RESULTS

The population pharmacokinetic models for each component of the 3D ± ribavirin regimen (DAAs and ritonavir, n = 2348) and ribavirin (n = 1841) adequately described their respective plasma concentration-time data. Model parameter estimates were precise and robust, and all models showed good predictive ability. Significant covariate effects associated with apparent clearance and volume of distribution included age, body weight, gender, cirrhosis, HCV subtype, opioid or antidiabetic agent use, and creatinine clearance.

CONCLUSION

The population pharmacokinetics of the 3D ± ribavirin regimen components in HCV-infected patients were characterized using phase II and III HCV clinical trial data. Although several statistically significant covariates were identified, their effects were modest and not clinically meaningful to necessitate dose adjustments for any component of the 3D regimen.

Variant Inosine Triphosphatase Phenotypes Are Associated With Increased Ribavirin Triphosphate Levels

Individuals with lower inosine triphosphatase (ITPA) enzyme activity have a reduced likelihood of experiencing hemolytic anemia during hepatitis C virus (HCV) treatment containing ribavirin (RBV). Because ITPA degrades purines and RBV is a purine analogue, it is conceivable that ITPA activity may affect intracellular RBV concentrations. Here we assessed the association between ITPA activity phenotype and concentrations of RBV triphosphate (RBV-TP) in red blood cells (RBCs) during HCV treatment. RBV-TP was quantified in the RBCs of 177 HCV-infected individuals at a median (range) of 84 (19 to 336) days into HCV treatment that included RBV. Mean (SD) RBV-TP concentrations were 92.8 (51.6), 101.3 (53.5), 184.8 (84.5), and 197.7 (64.6) pmol/106 cells for 100%, 60%, 30%, and ≤10% ITPA activity groups, respectively. Overall, RBV-TP was approximately 2-fold higher in patients with ≤30% ITPA activity compared to 100% activity (P < .0001). Despite higher RBV-TP levels, individuals with variant ITPA phenotypes had less anemia. The 100% activity group had, on average, a -2.20 g/dL drop in hemoglobin vs -1.43 g/dL (P = .04) for 60% activity, -1.14 g/dL (P = .008) for 30% activity, and -0.70 g/dL (P = .06) for ≤10% activity. This finding of higher RBV-TP concentrations in RBCs in ITPA variants was unexpected given that ITPA activity-deficient individuals have a reduced likelihood of RBV-induced anemia. It also refutes the hypothesis that the mechanism by which ITPA variants are protected against anemia is due to lower RBV-TP levels in RBCs.

Influence of Ribavirin Serum Levels on Outcome of Antiviral Treatment and Anemia in Hepatitis C Virus Infection

BACKGROUND

Ribavirin blood levels vary considerably between patients with standard weight-based dosing. Their impact on sustained virological response (SVR) with pegylated interferon and ribavirin is controversial, but has mostly been studied before the IL28b gene polymorphism as a possible confounder was discovered.

METHODS

The impact of serum ribavirin trough levels at week 4, at the end of treatment and of mean levels across the entire antiviral treatment with pegylated interferon and ribavirin on relapse, SVR rates and anemia was retrospectively studied by univariate and multivariable logistic regression analyses in 214 patients with HCV genotype 1-4 infection, including 88 patients with available IL28b genotyping.

RESULTS

Mean ribavirin levels varied between 0.68-5.65 mg/l and significantly differed between patients with or without SVR. By multivariable regression including age, sex, HCV viral load, HCV genotype, liver fibrosis stage, prior treatments, immunosuppression and IL28b genotype, ribavirin levels consistently displayed significant influence on SVR and relapse without indication for a specific importance of higher concentrations early or late in the treatment course. Although hemoglobin decline was on average more pronounced in patients with higher ribavirin levels, hemoglobin remained relatively stable in a significant proportion of these, indicating that ribavirin levels alone are insufficient to predict anemia.

CONCLUSION

While data are scarce to draw conclusions applicable for modern DAA therapies, these results support ribavirin treatment based on serum levels instead of purely weight-based dosing in combination with pegylated interferon.

Randomized Trial Evaluating the Impact of Ribavirin Mono-Therapy and Double Dosing on Viral Kinetics, Ribavirin Pharmacokinetics and Anemia in Hepatitis C Virus Genotype 1 Infection

In this pilot study (RibaC), 58 hepatitis C virus (HCV) genotype 1 infected treatment-naïve patients were randomized to (i) 2 weeks ribavirin double dosing concomitant with pegylated interferon-α (pegIFN-α), (ii) 4 weeks ribavirin mono-therapy prior to adding pegIFN-α, or (iii) standard-of-care (SOC) ribavirin dosing concurrent with pegIFN-α. Four weeks of ribavirin mono-therapy resulted in a mean 0.46 log₁₀ IU/mL HCV RNA reduction differentially regulated across IL28B genotypes (0.89 vs. 0.21 log₁₀ IU/mL for CC and CT/TT respectively; P = 0.006), increased likelihood of undetectable HCV RNA week 4 after initiating pegIFN-α and thus shortened treatment duration (P<0.05), and decreased median IP-10 concentration from 550 to 345 pg/mL (P<0.001). Both experimental strategies impacted on ribavirin concentrations, and high levels were achieved after one week of double dosing. However, by day 14, double dosing entailed a greater hemoglobin decline as compared to SOC (2.2 vs. 1.4 g/dL; P = 0.03). Conclusion: Ribavirin down-regulates IP-10, and may have an anti-viral effect differently regulated across IL28B genotypes.

Ribavirin Concentrations Do Not Predict Sustained Virological Response in HIV/HCV-Coinfected Patients Treated with Ribavirin and Pegylated Interferon in the Swiss HIV Cohort Study

Background

Ribavirin (RBV) is an essential component of most current hepatitis C (HCV) treatment regimens and still standard of care in the combination with pegylated interferon (pegIFN) to treat chronic HCV in resource limited settings. Study results in HIV/HCV-coinfected patients are contradicting as to whether RBV concentration correlates with sustained virological response (SVR).

Methods

We included 262 HCV treatment naïve HIV/HCV-coinfected Swiss HIV Cohort Study (SHCS) participants treated with RBV and pegIFN between 01.01.2001-01.01.2010, 134 with HCV genotype (GT) 1/4, and 128 with GT 2/3 infections. RBV levels were measured retrospectively in stored plasma samples obtained between HCV treatment week 4 and end of therapy. Uni- and multivariable logistic regression analyses were used to evaluate the association between RBV concentration and SVR in GT 1/4 and GT 2/3 infections. The analyses were repeated stratified by treatment phase (week 4-12, 13-24, >24) and IL28B genotype (CC versus CT/TT).

Results

SVR rates were 35.1% in GT 1/4 and 70.3% in GT 2/3 infections. Overall, median RBV concentration was 2.0 mg/L in GT 1/4, and 1.9 mg/L in GT 2/3, and did not change significantly across treatment phases. Patients with SVR had similar RBV concentrations compared to patients without SVR in both HCV genotype groups. SVR was not associated with RBV levels ≥2.0 mg/L (GT 1/4, OR 1.19 [0.5-2.86]; GT 2/3, 1.94 [0.78-4.80]) and ≥2.5 mg/L (GT 1/4, 1.56 [0.64-3.84]; GT 2/3 2.72 [0.85-8.73]), regardless of treatment phase, and IL28B genotype.

Conclusion

In HIV/HCV-coinfected patients treated with pegIFN/RBV, therapeutic drug monitoring of RBV concentrations does not enhance the chance of HCV cure, regardless of HCV genotype, treatment phase and IL28B genotype.

Induction dosing of peginterferon alfa-2a (40 KD) and/or high-dose ribavirin in genotype 1 CHC patients with difficult-to-treat characteristics: pharmacokinetic and viral kinetic (PK/VK) assessment from PROGRESS

BACKGROUND/AIMS

PROGRESS randomized chronic hepatitis C genotype 1 patients with a baseline viral load ≥400,000 IU/mL weighing ≥85 kg to regimens of 180 μg/week for 48 weeks or 360 μg/week for 12 weeks followed by 180 μg/week for 36 weeks peginterferon alfa-2a plus ribavirin. This analysis explored pharmacokinetics and early viral kinetics (VK) and evaluates differences between groups.

METHODOLOGY

Blood samples for pharmacokinetic and VK analyses were collected from 51 patients enrolled in the PROGRESS study.

RESULTS

Mean peginterferon alfa-2a trough concentration at week 12 was 11.7±4.3 ng/mL for 180 μg and 23.4±11.3 ng/mL for 360 μg. Early VK profiles suggested a trend towards an enhanced viral decline in the 360 μg groups with a mean decrease in HCV RNA at 48 hours post first dose of 1.04 log10 (IU/mL) compared with 0.76 log10 (IU/mL) in the 180 μg groups. Mean beta slope increased with dose, ranging from 0.38±0.26 log10 IU/week at 180 μg to 0.52±0.32 log10 IU/week at 360 μg.

CONCLUSIONS

Early viral de clines may be enhanced with the 360 μg dose. These data may suggest the utility of high-dose peginterfer on alfa-2a plus direct-acting antivirals (DAA) in select difficult-to-treat populations.

ITPA genotype protects against anemia during peginterferon and ribavirin therapy but does not influence virological response

On-treatment anemia is associated with higher sustained virological response (SVR) rates during peginterferon plus ribavirin (RBV) therapy. Inosine triphosphatase (ITPA) variants causing ITPase deficiency have been shown to protect against RBV-induced anemia. However, ITPase activity has not been associated with SVR. To study this discrepancy, we examined the relationships between ITPase activity, on-treatment anemia, SVR, and RBV levels in hepatitis C virus genotype 1 (HCV-1) patients from the CHARIOT study. ITPA genotype (rs7270101, rs1127354) was used to define ITPase activity in 546 patients. Plasma RBV levels were measured using high-performance liquid chromatography (HPLC). Relationships between ITPase activity, on-treatment hemoglobin (Hb) levels, RBV levels, and SVR were tested using regression modeling, survival analysis, and locally weighted scatterplot smoothing (LOWESS) plot analysis. Hb decline was independently associated with SVR (P<0.0001). ITPase deficiency was present in 35%. ITPase deficiency strongly protected against Hb decline (P<0.0001), but was not associated with SVR (P=0.28). The probability of SVR increased with lower nadir Hb for both wild-type and deficient ITPase activity, but the association curve shifted to describe a parallel relationship at higher Hb levels in patients with ITPase deficiency. In a subset (n=203), we tested the hypothesis that the association between Hb decline and SVR reflected RBV levels rather than actual Hb level. RBV levels were associated with on-treatment Hb decline and SVR, but not ITPase activity. In regression models, adjustment for RBV levels attenuated the association between Hb decline and SVR.

CONCLUSION

ITPase deficiency protects against RBV-induced anemia, but is not associated with SVR. Our data suggest that the relationship between Hb decline and SVR is not mechanistic, but is linked to RBV levels.

Pharmacokinetics and safety of single-dose ribavirin in patients with chronic renal impairment

This open-label study assessed the pharmacokinetics of a single 400-mg oral dose of ribavirin in 6 healthy volunteers and 18 subjects with varying degrees of renal impairment (mild:creatinine clearance [CLcr] 61-90 mL/min/1.73 m², moderate: CLcr 31-60 mL/min/1.73 m(2), severe: CLcr 10-30 mL/min/1.73 m², n = 6 in each group). Blood and urine samples were collected pre-dose and up to 168 hours post-dose for pharmacokinetic analyses. Compared with control subjects, ribavirin area under the plasma concentration-time curve from time zero to the time of the final quantifiable sample (AUC(tf)) and maximum plasma concentration (C(max)) values were increased, and apparent clearance (CL/F), clearance (CLr), and amount excreted (Ae) values were reduced in subjects with renal impairment. Mean ribavirin AUC(tf) was increased 2- to 3-fold in patients with moderate-severe renal impairment compared with control subjects. Ribavirin CL/F and CLr were significantly correlated with CLcr. Single-dose ribavirin was safe and well tolerated in all subjects. The pharmacokinetics of ribavirin were substantially altered in subjects with stable chronic renal impairment, possibly reflecting changes in ribavirin metabolism associated with renal impairment.

Multiplex liquid chromatography-tandem mass spectrometry assay for simultaneous therapeutic drug monitoring of ribavirin, boceprevir, and telaprevir

New directly acting antivirals (DAAs) that inhibit hepatitis C virus (HCV) replication are increasingly used for the treatment of chronic hepatitis C. A marked pharmacokinetic variability and a high potential for drug-drug interactions between DAAs and numerous drug classes have been identified. In addition, ribavirin (RBV), commonly associated with hemolytic anemia, often requires dose adjustment, advocating for therapeutic drug monitoring (TDM) in patients under combined antiviral therapy. However, an assay for the simultaneous analysis of RBV and DAAs constitutes an analytical challenge because of the large differences in polarity among these drugs, ranging from hydrophilic (RBV) to highly lipophilic (telaprevir [TVR]). Moreover, TVR is characterized by erratic behavior on standard octadecyl-based reversed-phase column chromatography and must be separated from VRT-127394, its inactive C-21 epimer metabolite. We have developed a convenient assay employing simple plasma protein precipitation, followed by high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) for the simultaneous determination of levels of RBV, boceprevir, and TVR, as well as its metabolite VRT-127394, in plasma. This new, simple, rapid, and robust HPLC-MS/MS assay offers an efficient method of real-time TDM aimed at maximizing efficacy while minimizing the toxicity of antiviral therapy.

Absence of Clinically Relevant Pharmacokinetic Interaction Between Ribavirin and Tenofovir in Healthy Subjects

This was a 36-day, open-label, fixed-sequence, multiple-dose drug interaction study in 23 healthy subjects to evaluate the effects of multiple doses of tenofovir disoproxil fumarate on the single-dose pharmacokinetics of ribavirin. Subjects received a 600-mg once-daily oral dose of ribavirin on days 1 and 22 and 300-mg once-daily oral doses of tenofovir disoproxil fumarate on days 17 through 24. Pharmacokinetic sampling was performed on days 1 through 4 and 22 through 25. Pharmacokinetics of ribavirin was not altered by its coadministration with tenofovir disoproxil fumarate as the point estimates (day 22 [test treatment]/day 1 [reference treatment]), and the 90% confidence interval for maximum observed concentration (0.95; 88.7-101) and area under the plasma concentration-time curve up to time of last measurable concentration (1.12; 106-117) were within the equivalence bounds of 80% to 125%. Tenofovir pharmacokinetics after ribavirin coadministration was similar to that observed in previous studies. These results indicate that coadministration of tenofovir disoproxil fumarate and ribavirin does not result in substantial changes to their individual pharmacokinetic profiles.

Pharmacokinetics and Safety of Viramidine, a Prodrug of Ribavirin, in Healthy Volunteers

Ribavirin, part of the current first-line combination therapy for the treatment of chronic hepatitis C, has side effects-in particular, hemolytic anemia-that is frequently dose limiting. Based on animal studies, viramidine, a prodrug of ribavirin, is converted to ribavirin in the liver. Viramidine dosing yielded 50% higher ribavirin levels in the monkey liver but only half in plasma and red blood cells compared to ribavirin dosing. At the same dose, it also had a safer profile than ribavirin in a 28-day toxicity study in monkeys. The current study was carried out to evaluate the safety, tolerability, and pharmacokinetics of viramidine in healthy male volunteers (n = 8-18 on viramidine vs. 2 on placebo at each dose level) after oral dosing of viramidine at 200, 600, and 1200 mg. There were no serious adverse events, and most adverse events were mild. The percentages of treatment-emergent events judged to be possibly related to the study drug were 50% in the 1200-mg group, 26% in the 600-mg group, and none in the 200-mg group. Viramidine was orally absorbed and rapidly converted to ribavirin with a t(max) of 1.5 to 3.0 hours for both viramidine and ribavirin in plasma. There was dose proportionality in plasma AUC(0-168 h) and C(max) for viramidine and in plasma AUC(0-168 h) for ribavirin. Plasma AUC(0-168 h) for ribavirin was two to four times higher than plasma AUC(0-168 h) for viramidine, indicating that viramidine is extensively metabolized to ribavirin and is a prodrug of ribavirin in man. Amounts of viramidine and ribavirin excreted in the urine were small (2%-5% of dose), indicating that the main route of elimination for both viramidine and ribavirin is metabolism. Both viramidine and ribavirin were excreted into urine through the mechanism of glomerular filtration. In addition, an evaluation of the effect of a high-fat meal on the pharmacokinetics of viramidine and ribavirin after oral dosing of viramidine at 600 mg was conducted in healthy male volunteers (n = 33-34) in a crossover study design. A high-fat meal increased viramidine plasma AUC(0-168 h) by 44% and C(max) by 20%. It also increased ribavirin plasma AUC(0-168 h) by 19% and C(max) by 43%. The clinical relevance of these increases is unknown.

Ascending Multiple-Dose Pharmacokinetics of Viramidine, a Prodrug of Ribavirin, in Adult Subjects With Compensated Hepatitis C Infection

The current study was carried out to evaluate pharmacokinetic profiles of viramidine and ribavirin in patients (n = 8 per dose group) with compensated hepatitis C infection following oral dosing of viramidine (400, 600, or 800 mg bid for 4 weeks). Pharmacokinetic parameters were determined on days 1 and 29 based on plasma, red blood cell, and urine concentrations of viramidine and ribavirin. The results indicate rapid absorption and conversion of viramidine to ribavirin after oral administration of viramidine. Viramidine and ribavirin exposure in plasma and RBCs generally increased from the 400- to 600-mg dose level of viramidine. However, no further increase in exposure was noted at the 800-mg dose. Long half-lives for viramidine (66-76 hours in plasma and 200-420 hours in red blood cells) and ribavirin (340-410 hours in plasma and 360-430 hours in red blood cells) were noted. A negligible amount of viramidine (1%-4% of dose) and a small amount of ribavirin (9%-14% of dose) were excreted in the urine. The renal clearance was low for both viramidine (5-8 L/h) and ribavirin (4-7 L/h). Significant accumulation of viramidine was noted in red blood cells (accumulation factor [R] = 5-8) but not in plasma (R = 2). Extensive accumulation of ribavirin was noted in both plasma (R = 9-17) and red blood cells (R = 77-129). Steady-state levels of ribavirin and viramidine in plasma and red blood cells were achieved by day 22. At steady state, there was extensive conversion of viramidine to ribavirin in both plasma and red blood cells. Both viramidine and ribavirin were preferentially distributed into red blood cells than plasma.

Negative predictive value of IL28B, SLC28A2, and CYP27B1 SNPs and low RBV plasma exposure for therapeutic response to PEG/IFN-RBV treatment

OBJECTIVES

The response rate to treatment of chronic hepatitis C virus-genotype 1 and 4 infections was recently found to be strongly influenced by many polymorphisms. The aim of our study was to carry out an integrated analysis of the effects of polymorphisms and ribavirin (RBV) plasma exposure on outcome.

METHODS

The retrospective analysis included 174 patients. IL28B, CYP27B1, SLC29A1, SLC28A3, and SLC28A2 polymorphisms were genotyped and tested for association with sustained virological response. The impact of RBV plasma exposure during the first 3 months of therapy on outcome was also investigated.

RESULTS

Considering patients infected by hepatitis C virus-1/4, 3 polymorphisms (IL28B rs8099917TT, CYP27B1 rs4646536TT, and CNT2 rs11854484TT) were associated with sustained virological response. The number of negative variant allele and low RBV exposure were correlated to percentage increasing to therapy failure, suggesting some degree of cumulative effect of the 4 factors. A cutoff of 2.5 μg/mL of RBV was found to be associated with outcome (area under ROC [AUROC] curve = 0.64, sensitivity = 55.0%, and specificity = 71.2%, P = 0.020). In multivariate logistic regression analyses, each variant allele and RBV plasma exposure cutoff were independently associated with outcome.

CONCLUSIONS

In this study, we found that additional polymorphisms and RBV plasma exposure are also able to influence the achievement of response. Regardless of the magnitude of RBV pharmacokinetic exposure, the negative predictive value of the polymorphisms here investigated is much stronger than the positive one.

Influence of HCV genotype 1 subtypes on the virus response to PEG interferon alpha-2a plus ribavirin therapy

New factors that influence the viral response in HCV non-genotype 2/3 patients must be identified in order to optimize anti-HCV treatment. This multicenter prospective study evaluates the influence of HCV variability and pharmacological parameters on the virological response of these patients to pegylated interferon α2a (peg-IFN-α2a: 180 µg/week) and ribavirin (RBV; 800-1,200 mg/day) for 48 weeks. HCV subtypes were identified by sequencing the NS5B region. Serum RBV and peg-IFN-α2a concentrations were measured at weeks 4 and 12. The 115 patients (67 men; median age = 49, range 31-76) included 64 who had never been treated and 27 co-infected with HIV. The mean baseline HCV RNA was 6.30 ± 0.06 log IU/ml and the HCV genotypes were: G1 (n = 93) with 1a (n = 37) and 1b (n = 50), G4 (n = 20) and G5 (n = 2). Most patients (79/108; 73%) had an early virological response. Independent predictors of an early virological response were interferon naive patients (OR=  2.98, 95% CI: 1.15-7.72) and RBV of >2,200 ng/ml at week 12 (OR = 3.41, 95% CI: 1.31-8.90). Forty of 104 patients (38%) had a sustained virological response. The only independent predictors of a sustained virological response were subtype 1b (OR = 6.82, 95% CI: 1.7-26.8), and HCV RNA <15 IU/ml at week 12 (OR = 25, 95% CI: 6.4-97.6). Thus a serum RBV concentration of >2,200 ng/ml was associated with an early virological response and patients infected with HCV subtype 1b had a better chance of a sustained virological response than did those infected with subtype 1a.

Ribavirin-induced anemia in hepatitis C virus patients undergoing combination therapy

The current standard of care for hepatitis C virus (HCV) infection – combination therapy with pegylated interferon and ribavirin – elicits sustained responses in only ∼50% of the patients treated. No alternatives exist for patients who do not respond to combination therapy. Addition of ribavirin substantially improves response rates to interferon and lowers relapse rates following the cessation of therapy, suggesting that increasing ribavirin exposure may further improve treatment response. A key limitation, however, is the toxic side-effect of ribavirin, hemolytic anemia, which often necessitates a reduction of ribavirin dosage and compromises treatment response. Maximizing treatment response thus requires striking a balance between the antiviral and hemolytic activities of ribavirin. Current models of viral kinetics describe the enhancement of treatment response due to ribavirin. Ribavirin-induced anemia, however, remains poorly understood and precludes rational optimization of combination therapy. Here, we develop a new mathematical model of the population dynamics of erythrocytes that quantitatively describes ribavirin-induced anemia in HCV patients. Based on the assumption that ribavirin accumulation decreases erythrocyte lifespan in a dose-dependent manner, model predictions capture several independent experimental observations of the accumulation of ribavirin in erythrocytes and the resulting decline of hemoglobin in HCV patients undergoing combination therapy, estimate the reduced erythrocyte lifespan during therapy, and describe inter-patient variations in the severity of ribavirin-induced anemia. Further, model predictions estimate the threshold ribavirin exposure beyond which anemia becomes intolerable and suggest guidelines for the usage of growth hormones, such as erythropoietin, that stimulate erythrocyte production and avert the reduction of ribavirin dosage, thereby improving treatment response. Our model thus facilitates, in conjunction with models of viral kinetics, the rational identification of treatment protocols that maximize treatment response while curtailing side effects.

The treatment of HCV infection poses a major global health-care challenge today. The current standard of care, combination therapy with interferon and ribavirin, works in only about half of the patients treated. Because no alternatives are available yet for patients in whom combination therapy fails, identifying ways to improve response to combination therapy is critical. Increasing exposure to ribavirin does improve response but is associated with the severe side-effect, anemia. One way to maximize treatment response therefore is to increase ribavirin exposure to levels just below where anemia becomes intolerable. A second way is to supplement combination therapy with growth hormones, such as erythropoietin, that increase the production of red blood cells (erythrocytes) and compensate for ribavirin-induced anemia. Rational optimization of combination therapy thus relies on a quantitative description of ribavirin-induced anemia, which is currently lacking. Here, we develop a model of the population dynamics of erythrocytes in individuals exposed to ribavirin that quantitatively describes ribavirin-induced anemia. Model predictions capture several independent observations of ribavirin-induced anemia in HCV patients undergoing combination therapy, estimate the threshold ribavirin exposure beyond which anemia becomes intolerable, suggest guidelines for the usage of growth hormones, and facilitate rational optimization of therapy.

Comparison of biochemical safety between PEG-IFN alpha-2a and PEG-IFN alpha-2b

BACKGROUND/AIMS

Although the efficacy and safety of pegylated-interferon (PEG-IFN) alpha-2a and PEG-IFN alpha-2b have been comparatively studied, there are few study results available in which the two PEG-IFN products were strictly compared. To compare the effects of two PEG-IFN products on blood cell profile.

METHODOLOGY

The time-course change in blood cell counts was compared between chronic hepatitis C patients with genotype 1b receiving PEG-IFN alpha-2a/ribavirin and PEG-IFN alpha-2b/ribavirin combination therapy. The comparison was made after matching patients from the two groups based on ribavirin apparent clearance (CL/F), a surrogate marker of the steady state blood ribavirin level, in order to eliminate the effect of ribavirin. Fifteen pairs of matched patients were selected.

RESULTS

The time-course change in hemoglobin did not differ significantly between the two groups. However, significantly greater reductions in both neutrophil and platelet counts were observed with PEG-IFN alpha-2a compared to PEG-IFN alpha-2b. A slightly longer period was required with PEG-IFN alpha-2a than with PEG-IFN alpha-2b for a reduction in neutrophil or platelet count large enough to necessitate dose reduction.

CONCLUSIONS

Two types of PEG-IFN products affected the blood cell profile in different manners. Long-term monitoring of laboratory test values is necessary with PEG-IFN alpha-2a.

Prediction of sustained virological response by ribavirin plasma concentration at week 4 of therapy in hepatitis C virus genotype 1 patients

BACKGROUND

Pegylated interferon/ribavirin combination is currently the standard treatment for chronic hepatitis C virus (HCV) infection. Body weight adjustment of ribavirin is crucial for response. However, previous studies found no relation between ingested dose and plasma concentration. The aim of this study was to define the ribavirin trough plasma concentration at week 4 (W4) associated with sustained virological response (SVR).

METHODS

Thirty-one HCV genotype 1 patients (8 naive and 23 non-responders to a previous pegylated interferon/ribavirin therapy) were treated with pegylated interferon/ribavirin and assessed by HPLC for ribavirin plasma concentration at W4.

RESULTS

Eleven patients (35%) achieved SVR, whereas 20 (65%) were non-responders. The median ribavirin plasma concentration at W4 (1.90 mg/l) varied from 1.62 mg/l in patients with subsequent non-response to 2.28 mg/l in sustained responders (P=0.007). Receiver operating characteristic curve analysis indicated that the 2.01 mg/l threshold gave the best sensitivity and specificity (73% and 80%, respectively, area under the curve =0.80; P=0.007). Sixty-seven percent of patients with median ribavirin plasma concentration >2 mg/l achieved SVR versus only 16% below this level (P=0.007). Multivariate regression analysis indicated that a ribavirin plasma concentration >2 mg/l at W4 was associated with SVR independent of gender, age, weight, baseline viral load and response to previous therapy.

CONCLUSION

These results, which remain to be confirmed in large clinical trials, highlight the potential relevance of ribavirin plasma level monitoring at an early stage of treatment. This monitoring could be of help in guiding antiviral therapy by offering dose adjustment in patients with ribavirin plasma level below the 2 mg/l threshold.

Low response to pegylated interferon plus ribavirin in HIV-infected patients with chronic hepatitis C treated with abacavir

BACKGROUND

There is little information about the influence of antiretroviral drugs on the antiviral activity of pegylated interferon (PEG-IFN) plus ribavirin (RBV) against hepatitis C virus (HCV).

METHODS

All HIV-infected patients with chronic hepatitis C who received first-line PEG-IFN plus RBV were retrospectively analyzed. Only patients in whom virological stopping rules were applied and who did not change their antiretrovirals were chosen. Plasma RBV concentrations were measured at week 4.

RESULTS

A total of 493 patients (78% males, mean age 41 years, 78% on antiretroviral therapy, mean CD4+ T-cell count 561 cells/microl) fit the study inclusion criteria. Mean baseline serum HCV RNA was 5.89 log10 IU/ml, 65% were infected by genotypes 1 or 4 and 40% had advanced liver fibrosis (Metavir F3F4). The overall rate of sustained virological response (SVR) was 38%. Factors associated with lack of SVR in the multivariate analyses (odds ratio [95% confidence interval], P-value) were higher baseline serum HCV RNA (2.42 per log10 IU/ml [1.31-4.46], 0.005), HCV genotypes 1 or 4 (5.95 [2.50-14.29], < 0.001) and lower RBV plasma trough concentrations (1.74 per microg/ml [1.15-2.63], 0.009). Interestingly, a trend was noticed for abacavir use (2.22 [0.91-5.40], 0.08), which become significant when only considering the subset of patients with RBV plasma levels < 2.3 microg/ml (7.63 [1.39-41.67], 0.02).

CONCLUSIONS

The use of abacavir might interfere with the anti-HCV activity of PEG-IFN plus RBV. As both antivirals are guanosine analogues, an inhibitory competition between abacavir and RBV might explain this observation, which is more prominent in patients with lower RBV exposure.

Measurement of ribavirin and evaluation of its stability in human plasma by high-performance liquid chromatography with UV detection

A simple high-performance liquid chromatography method for the determination of the antiviral agent ribavirin in human plasma was developed and validated. The method involved solid-phase extraction on phenyl boronic acid cartridges, a reversed-phase liquid chromatography with a Waters Atlantis dC18 (150 mm x 3.9 mm, 5 microm) column and a mobile phase consisting of 10 mM potassium phosphate buffer (pH 4.0), and ultraviolet detection at 207 nm. This assay proved to be sensitive (lower limit of quantification of 0.05 microg/ml), linear (correlation coefficients >or=0.997), specific (no interference with various potentially co-administrated drugs), reproducible (both intra-day and inter-day coefficients of variation <or=4.3%), and accurate (deviations ranged from -5.6 to 2.2% and from -6.0 to 4.0% for intra-day and inter-day analysis, respectively). The method was applied to therapeutic monitoring of patients undergoing ribavirin treatment for hepatitis C and proved to be robust and reliable. Thus, this method provides a simple, sensitive, precise and reproducible assay for dosing ribavirin that can be readily adaptable to routine use by clinical laboratories with standard equipment. In addition, we evaluated the stability of ribavirin in plasma under various conditions, since no detailed study on thermal stability of ribavirin has been reported so far and discrepant data do exist on ribavirin stability upon conditions that clinical samples commonly experience. Ribavirin was stable in human plasma stored at room temperature for at least 24 h or at -20 degrees C for up to 1 month, after three freeze-thaw cycles, as well as in samples undergoing heat inactivation of infectious viruses for 60 min at 60 degrees C. The drug was also stable in processed samples stored at -20 degrees C for 3 days (as dried extracts) or at 20 degrees C for 4 days (as reconstituted samples).

Analysis of ribavirin mutagenicity in human hepatitis C virus infection

The addition of ribavirin to alpha interferon therapy significantly increases response rates for patients with chronic hepatitis C virus (HCV) infection, but ribavirin's antiviral mechanisms are unknown. Ribavirin has been suggested to have mutagenic potential in vitro that would lead to "error catastrophe," i.e., the generation of nonviable viral quasispecies due to the increment in the number of mutant genomes, which prevents the transmission of meaningful genetic information. We used extensive sequence-based analysis of two independent genomic regions in order to test in vivo the hypothesis that ribavirin administration accelerates the accumulation of mutations in the viral genome and that this acceleration occurs only when HCV replication is profoundly inhibited by coadministered alpha interferon. The rate of variation of the consensus sequence, the frequency of mutation, the error generation rate, and the between-sample genetic distance were measured for patients receiving ribavirin monotherapy, a combination of alpha interferon three times per week plus ribavirin, or a combination of alpha interferon daily plus ribavirin. Ribavirin monotherapy did not increase the rate of variation of the consensus sequence, the mutation frequency, the error generation rate, or the between-sample genetic distance. The accumulation of nucleotide substitutions did not accelerate, relative to the pretreatment period, during combination therapy with ribavirin and alpha interferon, even when viral replication was profoundly inhibited by alpha interferon. This study strongly undermines the hypothesis whereby ribavirin acts as an HCV mutagen in vivo.

Mutagenic effect of ribavirin on hepatitis C nonstructural 5B quasispecies in vitro and during antiviral therapy

BACKGROUND AND AIMS

Addition of ribavirin to interferon alfa treatment has substantially increased sustained virologic response rates in patients with chronic hepatitis C (CHC). Ribavirin acts as an RNA virus mutagen in vitro, thereby leading to error catastrophe. However, data in CHC are controversial.

METHODS

The nonstructural (NS) 5B quasi-species heterogeneity was analyzed in Huh7 cells harboring a subgenomic hepatitis C virus (HCV) replicon system treated with ribavirin or levovirin. Accordingly, NS5B quasi-species were studied in 14 patients with CHC who received ribavirin alone or combined with pegylated interferon alfa both at baseline and during the first weeks of therapy. Analysis of NS3 quasi-species served as control.

RESULTS

Cultivation of HCV replicon cells with ribavirin led to higher NS5B mutational frequencies compared with levovirin-treated or untreated cells (P < .05). Patients receiving ribavirin monotherapy showed higher overall mutational frequencies within NS3 and NS5B during therapy as compared with baseline (P < .01). Proportions of ribavirin-specific G-to-A and C-to-T transitions increased (P < .01). Paired analysis confirmed significant mean increases of mutational frequencies of approximately 5%. Ribavirin serum concentrations were positively correlated with mutational frequency changes (P < .05). In patients receiving combination therapy, a decrease of NS5B mutational frequencies ( approximately 10%) and lower proportions of G-to-A and T-to-C mutations (P < .01) were detectable.

CONCLUSIONS

Ribavirin, but not its L-enantiomer levovirin, is a mutagen in HCV replicon cells. In patients with CHC, ribavirin monotherapy exhibits a moderate mutagenic effect early during therapy that is not detectable in combination with pegylated interferon alfa.

Simultaneous determination of ribavirin and ribavirin base in monkey plasma by high performance liquid chromatography with tandem mass spectrometry

For the first time, a liquid chromatographic method with tandem mass spectrometric detection (LC-MS/MS) for the simultaneous determination of ribavirin and rabavirin base was developed and validated over the concentration range of 10-5,000 ng/ml, respectively, using a 0.025 ml monkey plasma sample. Ribavirin, ribavirin base, and the internal standards were extracted from monkey plasma via protein precipitation. After evaporation of the supernatant, the extract was reconstituted with 5% methanol (containing 0.1% formic acid) and injected onto the LC-MS/MS system. Optimum chromatographic separation was achieved on a Waters Atlantis dc18 (150 mm x 2.1mm, 5 microm) column with mobile phase run in gradient with 100% water containing 0.5% formic acid (A) and 90% acetonitrile (containing 0.5% formic acid (B). The flow rate was 0.4-0.6 ml/min with total cycle time of approximately 7.0 min. Post-column addition of acetonitrile (containing 0.1% formic acid) at 0.3 ml/min was used to increase the ionization efficiency in the MS source. The method was validated for sensitivity, linearity, reproducibility, stability and recovery. Lack of adverse matrix effect and carry-over was also demonstrated. The intra-day and inter-day precision and accuracy of the quality control (QC) samples were <9.0% relative standard deviation (R.S.D.) and 10.8% bias for ribavirin, and 10.3% R.S.D. and 11.3% bias for ribavirin base. The current specific, accurate and precise assay is useful in support of the toxicokinetic and pharmacokinetic studies of these compounds.

Early monitoring of ribavirin serum concentration is not useful to optimize hepatitis C virus treatment in HIV-coinfected patients

BACKGROUND

Emerging data suggest that higher ribavirin (RBV) exposure could improve early hepatitis C virus (HCV) response. Furthermore, interindividual RBV bioavailability shows high variation, and dose-limiting haemolytic anaemia is a common adverse event. Therefore, it has been suggested that monitoring RBV serum levels could be used to drive dose modification and to optimize management of HCV-infected patients receiving combination treatment.

METHODS

To assess the effect of RBV serum levels on HCV RNA clearance at week 4 and 12 of treatment, and to determine the correlation between RBV serum concentration and haemoglobin decrease, RBV trough levels were measured by HPLC in stored serum samples obtained from 94 HCV-HIV-coinfected patients at week 4 and 12 of treatment with peginterferon-alpha2b (1.5 microg/kg/weekly) pIus ribavirin (800-1,200 mg/day).

RESULTS

The median RBV levels increased from 1.70 microg/ml at week 4 to 1.97 microg/ml at week 12 of treatment (P = 0.001) and were independently predicted by weight-adjusted dose of RBV and co-administration of tenofovir. Haemoglobin drop was higher among patients who received zidovudine and weakly correlated with RBV level. Although RBV concentration was lower in genotype 1 or 4 HCV-infected patients who cleared the virus at treatment week 4, the ability of this parameter to discriminate between responders and non-responders at treatment week 4 and 12 was poor.

CONCLUSION

Intracellular RBV accumulation early in treatment might improve the kinetics of HCV response in difficult to treat patients. Although this hypothesis and the potential interaction between RBV and tenofovir warrant further research, our data do not support RBV serum monitoring as a tool to optimize treatment in HCV-HIV-coinfected patients.

Pharmacokinetics of ribavirin in patients with hepatitis C virus

AIM

A population pharmacokinetic analysis was performed using plasma concentration data (n = 7025) from 380 patients to examine the relationship between ribavirin dose and its pharmacokinetics.

METHODS

Ribavirin pharmacokinetics were described by a three-compartment model with sequential zero-order and a first-order absorption processes. Interoccasion variability and food effects were included.

RESULTS

Lean body weight (range 41-91 kg) was the only covariate with a clinically significant influence on ribavirin pharmacokinetics, affecting clearance (15.3-23.9 l h(-1)) and the volume of the larger peripheral compartment.

CONCLUSION

The model provided a good description of the available data, confirmed by accurate estimates of parameter values and low residual variability (17%).

LC-MS/MS method for simultaneous determination of viramidine and ribavirin levels in monkey red blood cells

A high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed for the simultaneous determinations of total viramidine (viramidine, viramidine monophosphate, viramidine diphosphate, and viramidine triphosphate) and total ribavirin (ribavirin, ribavirin monophosphate, ribavirin diphosphate, and ribavirin triphosphate) in monkey red blood cells (RBC). The method involves the addition of internal standards and perchloric acid, conversion of viramidine or ribavirin phosphorylated metabolites to viramidine or ribavirin, purification with an aminopropyl (NH(2)) solid phase extraction (SPE) cartridge, and LC-MS/MS analysis. The MS/MS is selected to monitor m/z 245-->113, 250-->113, 244-->112, and 249-->112 for ribavirin, [(13)C]ribavirin, viramidine, and [(13)C]viramidine, respectively, using positive electrospray ionization. The calibration curves are linear over a concentration range of 100-10,000 ng/mL (0.412-41.2 microM) with a lower limit of quantification (LLOQ) of 100 ng/mL for both compounds. Mean inter-assay recoveries for ribavirin are 101%, 98.9%, and 96.0%, with coefficient of variance (%CV) values between 1.95 and 4.50% for 100, 1000, and 10,000 ng/mL quality control (QC) samples, respectively. Mean inter-assay recoveries for viramidine are 96.3%, 101%, and 102%, with coefficient of variation (%CV) values between 3.61 and 7.22%, for 100, 1000, and 10,000 ng/mL QC samples, respectively. Over-curve dilution QC at 400 microg/mL (1639 microM) for both viramidine and ribavirin are used to ensure the dilution accuracy (25 X dilutions) for monkey samples. The method has been used to simultaneously determine the total concentrations of ribavirin and viramidine in monkey RBC following 5, 15, and 36 weeks dosing of viramidine or ribavirin (60 mg/kg). The concentrations of total ribavirin following ribavirin dosing are 1242 microM at week 5, 1257 microM at week 15, and 1146 microM at week 36. The concentrations of total ribavirin following viramidine dosing are 634 microM at week 5, 716 microM at week 15, and 683 microM at week 36. Only small amounts of viramidine are detected in RBC following viramidine dosing, 7.80 microM at week 5, 6.63 microM at week 15, and 10.4 microM at week 36. The results suggest that ribavirin levels in RBC were at steady state at week 5 of ribavirin or viramidine dosing. At steady state, ribavirin levels in RBC are approximately 2x after ribavirin dosing than viramidine dosing. The relatively small percentage of viramidine in RBC suggests that viramidine either poorly penetrated into RBC or was extensively converted to ribavirin following entry into RBC.

Absorption, metabolism, and excretion of [14C]viramidine in humans

Absorption, metabolism, and excretion of [14C]viramidine, a prodrug of ribavirin, were studied in humans following a single oral dose (600 mg). Viramidine was rapidly absorbed, with a time to maximum concentration of the drug in plasma of 1.5 h. Viramidine and ribavirin accounted for only 4.3% and 42% of plasma area under the concentration-time curve (AUC) for radioactivity, respectively, indicating extensive conversion of viramidine to ribavirin, followed by further metabolism of ribavirin. The drug was largely trapped in red blood cells (RBC), with an RBC-to-plasma radioactivity AUC0-infinity ratio of 108. Excretion of total radioactivity in urine and feces accounted for 50.8% and 26.1% of the dose, respectively. The metabolic profile in urine (0 to 24 h) indicated that viramidine was excreted primarily as triazole carboxamide (TCONH2), triazole carboxylic acid nucleoside (TCOOH), and ribavirin with a small amount of unchanged viramidine, which each accounted for 64.1%, 17.0%, 15.7%, and 3.2% of urinary radioactivity, respectively. The amounts of unchanged viramidine (3.4% of dose) and ribavirin (10% of dose) in urine were small after oral administration of viramidine.

Plasma ribavirin concentrations during treatment of recurrent hepatitis C with peginterferon alpha-2b and ribavirin combination after liver transplantation

After liver transplantation (LT) for hepatitis C virus (HCV)-related cirrhosis, recurrence of HCV infection is universal. The efficacy of antiviral therapy in this indication is usually reduced because of its poor tolerability. We present herein the results of plasma measurement of ribavirin levels in transplanted patients when using increasing dosage of ribavirin, in comparison with a control cohort of nontransplanted patients. Seventeen control patients (nine women and eight men, median age 51.5 years) were compared with 12 liver transplant patients (2 women and 10 men, median age 55 years). In 76% of patients, HCV infection was genotype 1. All patients were treated by a combination of ribavirin and pegylated-interferon alpha-2b. A total of 54 blood samples were taken (1.8 per patient) for ribavirin level measurement. A virological response was obtained in 8/17 patients in the control group and in 6/12 LT patients. Ribavirin dose was lower in the LT group (8.79 vs 12.98 mg/kg/day), but plasma levels were the same in both groups (2.23 vs 2.43 mg/L for LT and non-LT groups, respectively). This was probably related to impaired renal function in the LT group (serum creatinine: 112.6 vs 73.6 micromol/L). No discontinuation of ribavirin therapy was observed and haemoglobin level was the same in both groups (109.5 g/L in LT patients vs 119.5 g/L in the control group). These results strongly support the interest in plasma measurement of ribavirin concentration during antiviral therapy in LT patients. Ribavirin dosage might be adapted without compromising its efficacy.

Validation of liquid/liquid extraction method coupled with HPLC-UV for measurement of ribavirin plasma levels in HCV-positive patients

Measurement of ribavirin plasma levels in HCV-positive patients have been shown to be useful in order to optimise individual ribavirin exposure. Efficacy and toxicity of this drug are shown to be concentration-dependant. A simple HPLC-UV method was developed and validated, which has an easy liquid/liquid extraction, sensitive limit of detection, without any interference peaks, reproducible and linear over the range of clinical relevant concentrations. The assay warrants further evaluation as a tool for ribavirin therapeutic drug monitoring in HCV-positive patients.

Ribavirin Levels and Haemoglobin Decline in Early Virological Responders and Non-Responders to Hepatitis C Virus Combination Therapy

Therapeutic drug monitoring of ribavirin has been claimed to predict virological response and/or haematological side effects in patients with chronic hepatitis C undergoing peginterferon/ribavirin combination treatment. In the present study, steady-state ribavirin levels were retrospectively analyzed in serum samples from patients at week 12 of combination therapy with peginterferon alpha-2a or alpha-2b and ribavirin. Patients were classified as early virological responders on the basis of undetectable HCV-RNA or HCV-RNA drop >or=2 log from baseline at week 12. The mean ribavirin level was not different between early virological responders (2.3 +/- 0.1 microg/ml, n = 45) and early virological non-responders (2.0 +/- 0.2 microg/ml, n = 10). There was no correlation between ribavirin levels at week 12 and early virological response. In patients with early virological response, haemoglobin (Hb) levels were found to be decreased by 18% on average from the basal values; however, in only 2 patients Hb levels declined below 100 g/l. There was a moderate negative correlation between ribavirin levels and Hb levels at week 12 (R = -0.50, p < 0.001); however, ribavirin levels did not correlate with relative or absolute decline in Hb as compared to basal levels or with ribavirin dose per kilogram body weight. In addition, a significant negative correlation between ribavirin levels and glomerular filtration rate was found (R = -0.31, p < 0.05). Based on our results, monitoring of ribavirin serum levels at week 12 of HCV combination therapy does not appear to predict early virological response or reductions in Hb levels. Further research is needed to assess their diagnostic value at other time points of peginterferon/ribavirin combination treatment and/or in patients with renal insufficiency.

Sensitive and specific LC–MS/MS method for the simultaneous measurements of viramidine and ribavirin in human plasma

Viramidine is a prodrug of ribavirin. To facilitate pharmacokinetics studies of viramidine in man, a sensitive and specific LC-MS/MS method for the simultaneous analyses of viramidine and ribavirin in human plasma was developed and validated. The method involved the addition of [13C]viramidine and [13C]ribavirin as internal standards, protein precipitation with acetonitrile, HPLC separation, and quantification by MS/MS system using positive electrospray ionization in the multiple reaction monitoring mode (MRM). The precursor-->product ion transitions were monitored at 245-->113, 250-->113, 244-->112, and 249-->112 for ribavirin, [13C]ribavirin, viramidine, and [13C]viramidine, respectively. The calibration curves for viramidine and ribavirin were linear over a concentration range of 1-1000 ng/mL. For both viramidine and ribavirin, the lower limit of quantification (LLOQ) was 1 ng/mL. For viramidine, intra- and inter-day analyses of QC samples at 1, 5, 250, and 1000 ng/mL indicated good precision (%CV between 1.0 and 7.0%) and accuracy (%bias between -4.3 and 5.2%). For ribavirin, intra- and inter-day analyses of QC samples at 1, 5, 250, and 1000 ng/mL indicated similar precision (%CV between 0.8 and 8.3%) and accuracy (%bias between -5.8 and 9.4%). Both viramidine and ribavirin were stable in human plasma stored at room temperature for at least 3 h, 4 degrees C for at least 6 h, and for at least three freeze-thaw cycles. This accurate and highly specific assay provides a useful method for evaluating the pharmacokinetics of viramidine and ribavirin in man following administration of viramidine.

Effect of ribavirin on intracellular and plasma pharmacokinetics of nucleoside reverse transcriptase inhibitors in patients with human immunodeficiency virus-hepatitis C virus coinfection: results of a randomized clinical study

The intracellular triphosphorylation and plasma pharmacokinetics of lamivudine (3TC), stavudine (d4T), and zidovudine (ZDV) were assessed in a pharmacokinetic substudy, in 56 human immunodeficiency virus-hepatitis C virus (HIV-HCV) coinfected patients receiving peginterferon alfa-2a (40KD) 180 microg/week plus either placebo or ribavirin (RBV) 800 mg/day in the AIDS PEGASYS Ribavirin International Coinfection Trial. There were no significant differences between patients treated with RBV and placebo in plasma pharmacokinetics parameters for the nucleoside reverse transcriptase inhibitors (NRTIs) at steady state (weeks 8 to 12): ratios of least squares mean of area under the plasma concentration-time curve (AUC(0-12 h)) were 1.17 (95% confidence interval, 0.91 to 1.51) for 3TC, 1.44 (95% confidence interval, 0.58 to 3.60) for d4T and 0.85 (95% confidence interval, 0.50 to 1.45) for ZDV, and ratios of least squares mean plasma C(max) were 1.33 (95% confidence interval, 0.99 to 1.78), 1.06 (95% confidence interval, 0.68 to 1.65), and 0.84 (95% confidence interval, 0.46 to 1.53), respectively. Concentrations of NRTI triphosphate (TP) metabolites in relation to those of the triphosphates of endogenous deoxythymidine-triphosphate (dTTP) and deoxcytidine-triphosphate (dCTP) were similar in the RBV and placebo groups. Differences (RBV to placebo) in least squares mean ratios of AUC(0-12 h) at steady state were 0.274 (95% confidence interval, -0.37 to 0.91) for 3TC-TP:dCTP, 0.009 (95% confidence interval, -0.06 to 0.08) for d4T-TP:dTTP, and -0.081 (95% confidence interval, -0.40 to 0.24) for ZDV-TP:dTTP. RBV did not adversely affect HIV-1 replication. In summary, RBV 800 mg/day administered in combination with peginterferon alfa-2a (40KD) does not significantly affect the intracellular phosphorylation or plasma pharmacokinetics of 3TC, d4T, and ZDV in HIV-HCV-coinfected patients.

Early monitoring of ribavirin plasma concentrations may predict anemia and early virologic response in HIV/hepatitis C virus-coinfected patients

Ribavirin (RBV) in combination with pegylated interferon alpha (pegIFN) is currently the standard treatment of hepatitis C virus (HCV) infection. The development of anemia requires a reduction in RBV doses in a substantial proportion of patients, limiting their chances of treatment response. The primary goal of this study was to assess if early monitoring of RBV plasma levels could help to predict anemia as well as early HCV RNA response in HIV/HCV-coinfected individuals. The secondary goal was to evaluate if antiretroviral drugs might influence RBV plasma levels. Plasma RBV concentrations were measured at weeks 4 and 12 in 98 HIV/HCV-coinfected individuals who initiated therapy with pegIFN-2a (180 microg/wk) plus RBV (800-1200 mg/d). RBV plasma levels correlated with RBV dose per kilogram of body weight (P = 0.02). Larger drops in hemoglobin levels were independently associated with higher RBV plasma levels and zidovudine (ZDV) use (P < 0.001). Likewise, higher RBV levels (P = 0.007) and HCV genotype 3 (P < 0.001) were found to be independent predictors of virologic response at week 4. Similar findings were obtained at week 12. Patients receiving ZDV concomitantly showed significantly higher RBV plasma concentrations compared with those who did not (3.28 mug/mL vs. 2.51 mug/mL; P = 0.002). RBV levels were not significantly altered by the coadministration of other nucleoside/nucleotide analogues. In summary, RBV plasma levels correlate with the development of anemia and with the achievement of an early virologic response. Therefore, early therapeutic drug monitoring might help to tailor RBV dosages, improving the efficacy and safety of anti-HCV treatment.

Ribavirin Levels in Post Liver Transplant Patients Treated for Recurrent Hepatitis C Viral Infection

Hepatitis C virus (HCV) infection is the most common indication for liver transplantation (LTx) in the United States. Ribavirin with pegylated interferon is the only treatment option for HCV recurrence in post-LTx patients. In clinical practice, for more than 50% of patients, ribavirin dose needs to be modified.

AIM

The aim of this study was to examine the role of ribavirin level and its relevance in the management of post-LTx patients in terms of renal dysfunction, efficacy, toxicity, and potential drug interactions.

PATIENTS AND METHODS

Thirty-four blood samples were available from 22 post-LTx patients. Ribavirin concentrations in plasma (all samples) and whole blood concentrations (16 samples) were examined. The dose of ribavirin ranged from 400 mg/d to 1000 mg/d, but concentrations were normalized to 800 mg/d.

RESULTS

There was a wide variation in plasma concentration of ribavirin, ranging from 1.8 to 122.1 mg/mL. The concentrations were similar in whole blood and plasma. Dose-normalized concentration with creatinine clearance below 70 mL/min were significantly higher when compared with creatinine clearance above 70 mL/min (P = .015). Eleven patients required erythropoietin; their mean ribavirin dosage was higher but mean ribavirin concentration was lower compared to the 11 patients who did not require erythropoietin factor. There was no difference in mean ribavirin concentration in patients who cleared the virus (n = 7) compared and who did not clear the virus (n = 9). Three patients were on nucleoside reverse transcriptase inhibitors (NRTI) had significantly higher concentration (mean 87.1 microg/mL) compared to those who did not receive NRTI (mean 34.4 microg/mL, P = .00)

CONCLUSION

Ribavirin concentration in plasma and whole blood were similar, with a wide variation. Patients with impaired renal function and those who were on NRTI had significantly higher concentrations of ribavirin. The ribavirin concentrations did not predict either the clearance of HCV RNA or the need for erythropoitin factor.

Significance of serum ribavirin concentration in combination therapy of interferon and ribavirin for chronic hepatitis C

OBJECTIVE

The purpose of this clinical retrospective cohort study was to determine the most suitable ribavirin concentration on combination therapy of interferon (IFN)-ribavirin.

METHODS

Entry criteria were serum HCV-RNA level >/=100 KIU/ml, HCV-genotype 1b, chronic hepatitis, and initial combination treatment of IFN-alpha-2b (6 million units daily for 2 weeks and then 3 times weekly for 6 weeks) and ribavirin (600-800 mg/day) for 8 weeks without stopping or decreasing the dosage of IFN and/or ribavirin. Sixty-eight consecutive patients who satisfied the above criteria were given maintenance therapy for another 16 weeks.

RESULTS

A sustained virological response (SVR) rate of 25.0% (17/68) was seen in all subjects. The SVR rate was 44.0% (11/25) in the high ribavirin group with a serum ribavirin concentration of >/=3,000 ng/ml at 8 weeks after initiation of combination therapy. SVR was significantly dependent at a serum ribavirin level of >/=3,000 ng/ml (p = 0.005). The incidence of discontinuations and dose modifications for combination therapy in patients having a serum ribavirin concentration of >/=3,500 ng/ml 8 weeks after initiation of therapy was 57.1% (4/7). This value was statistically higher than that in patents with <3,500 ng/ml (p = 0.033).

CONCLUSION

Our results showed that the most suitable serum ribavirin concentrations are from 3,000 to 3,500 ng/ml 8 weeks after initiation of combination therapy.

Liquid chromatography assay for routine monitoring of cellular ribavirin levels in blood

Ribavirin-induced hemolytic anemia is one cause for cessation of combination therapy with alpha interferon 2b and ribavirin for hepatitis C infection. Determining cellular ribavirin levels in blood, including the levels of its phosphorylated metabolites, might be useful for predicting ribavirin-induced anemia, because the metabolites accumulate in erythrocytes. We simplified an assay method developed previously to make it suitable for routine monitoring of cellular ribavirin. Whole blood diluted with a sixfold volume of ice-cold distilled water was subjected to acid phosphatase digestion to convert phosphorylated ribavirin metabolites to free ribavirin. The resulting mixture, spiked with an internal standard, was treated by phenyl boronic acid column extraction, followed by reverse-phase high-performance liquid chromatography analysis. The calibration curve for ribavirin levels in whole blood was linear at concentrations of 5.3 to 1,024 microM (r(2) = 0.9999). Validation coefficients of variation for intra- and interday assays were 2.9 to 5.8% and 4.3 to 8.3%, respectively. We tested this method by monitoring blood ribavirin concentrations in two hepatitis C patients receiving alpha interferon 2b-plus-ribavirin combination therapy.

A Comparison of the Exponential Decay Slope between PEG-IFN alfa-2b/Ribavirin and IFN alfa-2b/Ribavirin Combination Therapy in Patients with Chronic Hepatitis C Genotype 1b Infection and a High Viral Load

OBJECTIVES

A high virological response rate can often be shown to be obtained with PEG-IFN alpha-2b and ribavirin combination therapy in chronic hepatitis C patients. Viral dynamics have been utilized for the evaluation of antiviral effects, especially the exponential second decay slope, which represents the elimination of infected cells.

METHODS

Forty-nine patients were randomly assigned to the IFN alpha-2b group (n = 26) or the PEG-IFN alpha-2b group (n = 23). Ribavirin was administered equally to both groups. Measuring the serum concentration of HCVRNA, the exponential viral decay during phase 1 and 2 was calculated.

RESULTS

The exponential decay slope in phase 2 during the first 2 weeks was greater in the IFN alpha-2b group than in the PEG-IFN alpha-2b group; however, from weeks 3 to 4, it was greater in the PEG-IFN alpha-2b group than in the IFN alpha-2b group. Interestingly, in the PEG-IFN alpha-2b group, the exponential decay slope was greater from weeks 3 to 4 after initiating combination therapy than during the weeks 1-2 (p < 0.01), despite administration of the same PEG-IFN alpha-2b dose (1.5 microg/kg once weekly).

CONCLUSIONS

In PEG-IFN alpha-2b and ribavirin combination therapy, elimination of infected cells may be pronounced following an increase in serum ribavirin concentration in chronic hepatitis C patients with genotype 1b infection and a high viral load.

Disposition and metabolic profiles of [14C]viramidine and [14C]ribavirin in rat and monkey red blood cells and liver

The disposition and metabolic profiles of [14C]viramidine and [14C]ribavirin were compared in rat and monkey red blood cells and liver. Our data reveal that the total ribavirin-related components (ribavirin plus its mono-, di-, and triphosphate metabolites) may account for most of the drug in monkey liver following prolonged oral administration of viramidine.

Determination of ribavirin in human serum and plasma by capillary electrophoresis

The electrophoretic separation of ribavirin and 5-methylcytidine (internal standard) by capillary electrophoresis was examined. Separation was achieved using reverse polarity in a 100 mM borate electrolyte, pH 9.1, with 5 mM spermine added to reduce the electroosmotic flow. Sample preparation based on acetonitrile protein precipitation was found to be unsuitable for ribavirin analysis in patient samples due to insufficient sensitivity and interferences. Solid-phase extraction employing phenyl boronic acid cartridges provided cleaner separations. Using this approach with 500 microL sample and reconstitution of the dried extract into 100 microL of 33% v/v 100 mM phosphate buffer, pH 6.4 / 67% v/v acetonitrile, the detection and quantitation limits were determined to be 0.05 and 0.10 microg/mL, respectively, a sensitivity that is suitable for therapeutic drug monitoring of ribavirin in human plasma and serum samples. The method was validated and compared to a high-performance liquid chromatography (HPLC) method, showing excellent agreement between the two for a set of samples that stemmed from patients being treated with ribavirin and interferon-alpha-2b for a hepatitis C virus infection.

Ribavirin pharmacokinetics in renal and liver transplant patients: evidence that it depends on renal function

BACKGROUND

Ribavirin is approved for the treatment of chronic hepatitis C virus (HCV) infection. However, no recommendation exists for dosing patients with impaired renal function.

METHODS

The authors performed a pharmacokinetic study in 21 HCV-positive renal or liver transplant patients. The mean creatinine clearance (ClCr) calculated by the Cockcroft-Gault equation was 57 mL/min (0.95 mL/s; range, 17 to 89 mL/min [0.28 to 1.48 mL/s]). Twelve blood samples were obtained during a 96-hour period after the first single administration of 1,000 mg of ribavirin. After the first pharmacokinetics (PK) and the pharmacodynamics (PD) profile was completed, the patients received ribavirin at 1,000 mg/d with or without interferon-alpha. A blood sample was taken monthly just before the oral administration of ribavirin. Plasma ribavirin concentrations were determined by high-performance liquid chromatography.

RESULTS

A total of 428 plasma concentrations were analyzed by a population pharmacokinetic method using the NONlinear Mixed Effect Model program. The mean observed ribavirin apparent clearance (CL/F) was 9.1 L/h (with an interindividual variability of 39%). The influences of the age, sex, body weight (BW), serum creatinine (Scr), ClCr, hemoglobin, and graft status on CL/F were examined. CL/F was highly correlated with ClCr (r = 0.63, P < 0.01). The final regression formula was CL/F (L/h) = 32.3 x BW x (1 - 0.0094 x age) x (1 - 0.42 x sex)/Scr, where sex = 0 for men and 1 for women; Scr is in micromoles per liter. Sex had a larger influence on CL/F than that corresponding to the Cockcroft-Gault equation (ie, 15%).

CONCLUSION

The authors present the parameters that determine ribavirin clearance in HCV+ transplant patients with normal or impaired renal function. Moreover, we suggest ribavirin daily doses according to various levels of renal function.

Marked elevation of erythrocyte ribavirin levels in interferon and ribavirin-induced anemia

BACKGROUND & AIMS

To elucidate the effects of blood ribavirin disposition on ribavirin-induced anemia, the relationship between erythrocyte ribavirin concentration and change in hematologic parameters was examined in interferon and ribavirin combination therapy for HCV eradication.

METHODS

Nine HCV RNA-positive patients were treated with combination therapy including 11.3 +/- 1.2 mg.kg(-1).day(-1) of ribavirin. Blood concentrations of ribavirin and its phosphorylated metabolites were measured in plasma as well as erythrocyte.

RESULTS

Blood ribavirin concentrations gradually increased to steady-state levels of 8.8 +/- 1.4 micromol/L and 1389 +/- 371 micromol/L in plasma and erythrocytes, respectively, within 3-4 weeks of initiating therapy. Erythrocyte phosphorylated metabolite levels (1215 +/- 302 micromol/L) were found to be exceedingly high, i.e., 87% of the measured erythrocyte ribavirin concentration. In contrast, plasma phosphorylated metabolite levels were undetectable. Positive correlation was found to exist between erythrocyte ribavirin concentrations and a decrease in hemoglobin (r = 0.620, P < 0.001).

CONCLUSIONS

We concluded that marked elevation of erythrocyte ribavirin including its phosphorylated metabolites was associated with hemoglobin reduction, leading to interferon and ribavirin-induced anemia.

Evidence that plasma concentration rather than dose per kilogram body weight predicts ribavirin-induced anaemia

Ribavirin in combination with interferon alpha-2 or pegylated interferon is the standard treatment for chronic hepatitis C. The current dosage recommendations for ribavirin are based on body weight (bw). Ribavirin is mainly eliminated by the kidneys and we have recently shown that ribavirin plasma concentrations are determined primarily by renal function. It is therefore reasonable to hypothesize that side-effects of ribavirin, i.e. anaemia, should be more closely related to plasma concentrations of ribavirin than to the dose per kg bw. A total of 108 consecutive patients eligible for treatment of chronic hepatitis C were studied. Ribavirin concentrations in plasma were measured by high-performance liquid chromatography (HPLC)-UV after solid-phase extraction in trough samples taken 4, 8 and 12 weeks after the treatment commenced. A total of 213 samples were obtained and the change in the haemoglobin level and the creatinine concentration was measured in addition to ribavirin. The dose of ribavirin per kg bw did not correlate with the drop in haemoglobin level induced by ribavirin. The concentration of ribavirin was non-linearly related to the drop in the haemoglobin level as revealed by fitting a standard Hill equation type dose-response curve. The half maximal drop in haemoglobin was obtained at 4.4 microm. The results from this study suggest that the anaemia induced by ribavirin depends primarily on the concentration of ribavirin, and not on the dose per kg bw. This lends further support to the idea that ribavirin should be dosed according to renal function.

Comparative Pharmacokinetic Analysis by Standard Two-Stage Method versus Nonparametric Population Modeling

STUDY OBJECTIVE

To compare the two-stage method, a widely used analytical method in pharmacokinetic studies, with nonparametric population modeling by using the same data set for determining the oral bioavailability of ribavirin.

DESIGN

Pharmacokinetic analysis. Clinical research center.

MATERIAL

Oral bioavailability data of ribavirin determined previously in six healthy adults.

INTERVENTION

After 13C3-ribavirin 150 mg intravenously and unlabeled ribavirin 400 mg orally had been given 1 hour apart, serial serum and urine samples were obtained for up to 169 hours. Concentrations of 13C3-ribavirin and unlabeled ribavirin in serum and urine were determined by a high-performance liquid chromatography tandem mass spectrometric method.

MEASUREMENTS AND MAIN RESULTS

Serum and urine concentration-time profiles were comodeled with a three-compartment model. The analysis was performed again by using the nonparametric population analysis technique. Serum ribavirin concentrations underwent Monte Carlo simulation for 1000 subjects receiving a single 600-mg oral dose. Both methods were similar in determining the mean +/- SD bioavailability (51.8 +/- 21.8% by the two-stage method vs 54.8 +/- 16.4% by nonparametric modeling, p=0.79). However, the estimates of dispersion of model parameters and simulated drug exposures were substantially reduced by the population-modeling technique, as it takes into account covariance among model parameters and intersubject variability.

CONCLUSION

Although the study sample was small, our parallel analyses of the same data set clearly demonstrated that more precise parameter estimates are likely to result with the population-modeling technique. Having accurate and precise estimation of population pharmacokinetic parameters and their true variances is crucial, as, at any dose, there'will be a lower probability of encountering a concentration-driven toxicity because of fewer outliers as the variance associated with the parameters decreases.

A sensitive and specific method for the determination of total ribavirin in human red blood cells by liquid chromatography-tandem mass spectrometry

A sensitive and specific method using high-performance liquid chromatography (LC)-tandem mass spectrometry (MS) for the analysis of total ribavirin in human red blood cells (RBC) is developed and validated. The method involves the addition of an internal standard and perchloric acid, the conversion of ribavirin phosphorylated metabolites to ribavirin, purification with a solid-phase exchange cartridge, and LC-MS-MS analysis. The MS-MS is selected to monitor m/z 245-113 for ribavirin and m/z 250-113 for [13C]ribavirin using positive electrospray ionization. The calibration curve is linear over a concentration of 100-10,000 ng/mL with a limit of quantitation of 100 ng/mL. Mean interassay accuracy for quality control (QC) at 100, 1000, and 10,000 ng/mL are 101.8%, 99.4%, and 98.8%, respectively. Mean interassay precision (%CV) for QC at 100, 1000, and 10,000 ng/mL are 5.0%, 5.0%, and 2.5%, respectively. Extractibility of total ribavirin from RBC is confirmed with RBC obtained from a [(14)C]ribavirin-dosed monkey. The method is used to determine the free and total ribavirin concentration in human RBC obtained from hepatitis C patients treated with ribavirin.

Absorption, pharmacokinetics and excretion of levovirin in rats, dogs and cynomolgus monkeys

The absorption, pharmacokinetics and excretion of levovirin were studied in Sprague-Dawley rats (30 mg/kg) and Beagle dogs (30 mg/kg) following intravenous (iv) and oral administration of [(3)H]levovirin, and in Cynomolgus monkeys following iv and oral administration of [(14)C]levovirin. Oral absorption was 31.3% in rats, 67.3% in dogs and 17.5% in monkeys, and the bioavailability was 29.3% in rats, 51.3% in dogs and 18.4% in monkeys. After iv administration, the elimination half-life (t(1/2)) was 1.47 h in rats, 3.70 h in dogs and 3.50 h in monkeys. The total body clearance was 8.24, 2.96 and 2.58 mL/min per kg, respectively, in rats, dogs and monkeys and the apparent volume of distribution was 0.79, 0.95 and 0.65 L/kg. No metabolite was detected in plasma or urine of rats, dogs or monkeys, indicating negligible metabolism of levovirin in these animals. Excretion of total radioactivity in urine after oral dosing accounted for 15.4% of the administered dose in rats, 49.9% in dogs and 21.4% in monkeys. Biliary excretion did not play a significant role in the elimination of levovirin.

Ribavirin quantification in combination treatment of chronic hepatitis C

Ribavirin in combination with alpha 2 interferon is the consensus treatment for chronic hepatitis C. However, recent preliminary pharmacological studies have suggested that the bioavailability of ribavirin displays great interindividual variability. In order to monitor serum ribavirin levels during combination treatment, we developed and validated a quantitative assay using an approach adaptable for routine hospital laboratories. The method involved solid-phase extraction on phenyl boronic acid cartridges followed by high-performance liquid chromatography with a C(18)-bonded silica column and a mobile phase containing 10 mM ammonium phosphate buffer (with the pH adjusted to 2.5) and UV detection (207 nm). The sensitivity, recovery, linearity of the calibration curve, intra- and interassay accuracies, precision, and stability at 4 degrees C were consistent with its use in the laboratory routine. In addition, other nucleoside analogues sometimes used with ribavirin in patients coinfected with hepatitis C virus (HCV) and human immunodeficiency virus did not interfere with the quantification of ribavirin levels. The ribavirin concentration was quantified in 24 serum samples from patients with chronic hepatitis C treated with a combination of ribavirin and alpha 2 interferon. The mean serum ribavirin concentration was 2.67 +/- 1.06 micro g/ml (n = 24) at week 12 of treatment (W12) and 3.24 +/- 1.35 micro g/ml (n = 24) at week 24 of treatment (W24). In addition, ribavirin concentrations displayed high interindividual variabilities: the coefficients of variation of the serum ribavirin concentrations adjusted to the administered dose were 44 and 48% at W12 and W24, respectively. Moreover, the ribavirin concentration was higher in patients with a sustained virological response (n = 11) than in patients with treatment failure (n = 13), with significant intergroup differences at W12 (P = 0.030) and W24 (P = 0.049). The present study describes a simple analytical method for the quantification of ribavirin in human serum that could be a useful tool for the monitoring of ribavirin concentrations in HCV-infected patients in order to improve the efficacy and safety of therapy with ribavirin plus interferon.

Specific, sensitive and accurate liquid chromatographic-tandem mass spectrometric method for the measurement of ribavirin in rat and monkey plasma

Ribavirin is a purine nucleoside analog with broad spectrum activity against a spectrum of DNA and RNA viruses. To facilitate pharmacokinetics studies, a LC-MS-MS method for the analysis of ribavirin in rat and monkey plasma was developed and validated. The method involved the addition of acyclovir as an internal standard and protein precipitation with acetonitrile followed by separation by an Intertsil Silica column and quantification by a MS-MS equipped with a positive electrospray ionization in the multiple reaction monitoring mode. The MS-MS reaction was selected to monitor the 245-->113 and 226-->152 transitions for ribavirin and internal standard, respectively. The calibration curve was linear over a concentration range of 10-5000 ng/ml. The lower limit of quantitation was 10 ng/ml, the coefficient of variation (CV) was 8-11%, and the bias was 1-3%. Intra-day and inter-day analysis of QC samples at 30, 1500 and 3500 ng/ml indicate that the method was precise (CV<18%) and accurate (bias<13%). Ribavirin in rat and monkey plasma was stable at 5 degrees C for at least 24 h, 0 degrees C for at least 4 h, and after three freeze-thaw cycles. This specific, accurate and precise assay is useful in the study of the pharmacokinetics of this compound.

Specific, sensitive and accurate LC-MS/MS method for the measurement of levovirin in rat and monkey plasma

Levovirin is a guanosine nucleoside analogue and the L-enantiomer of ribavirin. Levovirin has a better safety profile than ribavirin, exerts similar immunomodulatory effects in a mouse efficacy model, and may provide a better therapeutic option than ribavirin in patients with chronic hepatitis C virus (HCV) infection. To facilitate pharmacokinetic studies, a LC-MS/MS method for the analysis of levovirin in rat and monkey plasma was developed and validated. The method involved adding ICN 10537 as an internal standard, protein precipitation with acetonitrile followed by separation on an Intersil Silica column, and quantification by a MS/MS system equipped with positive electrospray ionization (ESI) in the multiple reaction monitoring (MRM) mode. The MS/MS reaction was selected to monitor the 245-->113 and 259-->128 transitions for levovirin and internal standard, respectively. The calibration curve was linear over a concentration range of 10-5000 ng/ml. The limit of quantitation was 10 ng/ml, the coefficient of variation (CV) was 3-5%, and the bias was 3-6%. Intra- and inter-day analysis of QC samples at 30, 1500 and 3500 ng/ml indicated that the method was precise (CV<6%) and accurate (bias <9%). Levovirin in rat and monkey plasma was stable at 5 degrees C for at least 24 h, 0 degrees C for at least 4 h, and after three freeze-thaw cycles. This specific, accurate and precise assay is useful in the study the pharmacokinetic characteristics of this compound.

Development and validation of a liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for the determination of ribavirin in human plasma and serum

A liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed for the analysis of antiviral agent ribavirin in human plasma and serum. The samples (0.1 ml) were extracted from the matrix using a simple protein precipitation procedure. The supernatants were evaporated to dryness, reconstituted and injected onto the LC/MS/MS system. The chromatography separation was achieved on a silica column operated with an aqueous-organic mobile phase. The use of a silica column not only provided adequate retention for the extremely polar compound of ribavirin, but also enhanced electrospray ionization sensitivity with the use of high percentage organic solvent in the mobile phase. The method has been validated over the concentration range of 10-10000 ng/ml ribavirin in human plasma and serum. Bamethan was used as the internal standard. The protein precipitation extraction has been automated based on 96-well format with the use of robotic liquid handlers to improve the overall throughput of the analysis.

High-dose intravenous ribavirin therapy for subacute sclerosing panencephalitis

Two patients with subacute sclerosing panencephalitis (SSPE) were treated safely and effectively with high doses of intravenous ribavirin combined with intraventricular alpha interferon. The ribavirin concentrations maintained in the serum and cerebrospinal fluid were higher than those which inhibit SSPE virus replication in vitro and in vivo.