Pharmacokinetics of low-dose doxorubicin and metabolites in patients with AIDS-related Kaposi sarcoma

PURPOSE

Systemic chemotherapy is the treatment of choice for AIDS-related advanced Kaposi sarcoma. One principal schedule combines adriamycin (doxorubicin), bleomycin, and vincristine (ABV). We analysed the plasma concentrations of low-dose doxorubicin (Dx) and its metabolites doxorubicinol, 7-deoxydoxorubicinone, doxorubicinone, doxorubicinolone, and 7-deoxydoxorubicinolone in AIDS-patients to define patient-group and dose-specific pharmacokinetic parameters.

MATERIALS AND METHODS

A previously described high-performance liquid chromatographic (HPLC) method and a population approach with non-linear mixed effects modelling (NONMEM) were used for analysis and subsequent modelling of the time-concentration data of low-dose Dx and metabolites in seven patients with AIDS-related advanced Kaposi sarcoma. Patients received Dx 20 mg m(-2), bleomycin 15 U m(-2) and vincristine 2 mg as a 30-min intravenous infusion each. Blood samples were collected up to 72 h after the start of Dx treatment. WinNonlin software version 4.1 was used for non-compartmental analysis and NONMEM software version V for compartmental analysis. Covariate analysis was performed for various clinical and laboratory parameters.

RESULTS

Non-compartmental analysis yielded an area under the plasma concentration-time curve (AUC) for Dx of 566 mug h L(-1), a maximum plasma concentration (c(max)) of 599 mug L(-1) and an elimination half-life (t(1/2)) of 30.8 h. Compartmental analysis resulted in a two-compartment model with first-order elimination, which best fitted the concentration-time data. Model estimate for Dx clearance was 61.8 L h(-1), for intercompartmental clearance (Q) 112 L h(-1), for the volume of the central compartment (V(1)) 23.3 L, and for the volume of the peripheral compartment (V(2)) 1,130 L. Metabolite data could adequately be estimated by NONMEM using single-compartment models. Graphical plots of residuals versus time for all metabolites yielded no evidence of non-linear pharmacokinetic behaviour. Laboratory parameters of liver and renal function were all in the normal range and their inclusion in the pharmacokinetic model did not improve data fit. A final jack-knife analysis was performed.

CONCLUSIONS

Concentration-time data for low-dose Dx and metabolites in the ABV-regimen are best described by a two-compartment model with first-order elimination. The results confirm that the aglycones doxorubicinone, 7-deoxydoxorubicinone, and doxorubicinolone can be reliably detected in the studied patient group and implemented into a common metabolic model. Model estimates suggest that pharmacokinetic parameters are similar for low-dose Dx and higher-dosed Dx. As the role of the aglycones is still poorly understood, despite their potential clinical relevance, their analysis should be implemented in future pharmacokinetic and pharmacodynamic studies of Dx.

Practical guidelines to interpret plasma concentrations of antiretroviral drugs

Several relationships have been reported between antiretroviral drug concentrations and the efficacy of treatment, and toxicity. Therefore, therapeutic drug monitoring (TDM) may be a valuable tool in improving the treatment of HIV-1-infected patients in daily practice. In this regard, several measures of exposure have been studied, e.g. trough and maximum concentrations, concentration ratios and the inhibitory quotient. However, it has not been unambiguously established which pharmacokinetic parameter should be monitored to maintain optimal viral suppression. Each pharmacokinetic parameter has its pros and cons. Many factors can affect the pharmacokinetics of antiretroviral agents, resulting in variability in plasma concentrations between and within patients. Therefore, plasma concentrations should be considered on several occasions. In addition, the interpretation of the drug concentration of a patient should be performed on an individual basis, taking into account the clinical condition of the patient. Important factors herewith are viral load, immunology, occurrence of adverse events, resistance pattern and comedication. In spite of the described constraints, the aim of this review is to provide a practical guide for TDM of antiretroviral agents. This article outlines pharmacokinetic target values for the HIV protease inhibitors amprenavir, atazanavir, indinavir, lopinavir, nelfinavir, ritonavir and saquinavir, and the non-nucleoside reverse transcriptase inhibitors efavirenz and nevirapine. Detailed advice is provided on how to interpret the results of TDM of these drugs.

Significant induction of cyclophosphamide and thiotepa metabolism by phenytoin

PATIENT AND METHOD

A 42-year-old male patient with relapsing germ-cell cancer was enrolled in a salvage protocol that employed two 4-day courses of CTC high-dose chemotherapy with cyclophosphamide (1,500 mg m(-2) day(-1)), thiotepa (120 mg m(-2) day(-1)), and carboplatin, followed by peripheral blood progenitor cell support. From five days before the start of the second CTC course the patient received phenytoin for generalized epileptic seizures. Blood samples were collected on day 1 of both CTC courses and analyzed for cyclophosphamide and its activated metabolite 4-hydroxycyclophosphamide, and for thiotepa and its main active metabolite tepa.

RESULTS

Exposure (expressed as area under the plasma concentration vs time curve) to 4-hydroxycyclophosphamide and tepa in the second CTC course was increased by 51% and 115%, respectively, compared with the first CTC course, whereas exposure to cyclophosphamide and thiotepa was significantly reduced (67% and 29%, respectively). Because high exposure to 4-hydroxycyclophosphamide and tepa correlates with increased toxicity, the treatment risk of this patient was significantly increased. Therefore doses were reduced on the third day of the second course.

CONCLUSION

It was concluded that phenytoin significantly induces both cyclophosphamide and thiotepa metabolism, most probably by induction of the cytochrome p450 enzyme system. This potential clinical significant interaction should be taken into account when phenytoin is administered in combination with cyclophosphamide and thiotepa in clinical practice.

Integrated Population Pharmacokinetic Model of both cyclophosphamide and thiotepa suggesting a mutual drug-drug interaction

PURPOSE/AIMS

Cyclophosphamide (CP) and thiotepa (TT) are frequently administered simultaneously in high-dose chemotherapy regimens. The prodrug CP shows strong autoinduction resulting in increased formation of its activated metabolite 4-hydroxycyclophosphamide (4OHCP). TT inhibits this bioactivation of CP. Previously, we successfully modelled CP bioactivation and the effect of TT on the autoinduction. Recently we suggested that CP may also induce the conversion of TT in to its metabolite tepa (T). The aim of the current study was to investigate whether the influence of CP on TT metabolism can be described with a population pharmacokinetic model and whether this interaction can be incorporated in an integrated model describing both CP and TT pharmacokinetics.

METHODS

Plasma samples were collected from 49 patients receiving 86 courses of a combination of high-dose CP (4000 or 6000 mg/m2), TT (320 or 480 mg/m2) and carboplatin (1067 or 1600 mg/m2) given in short infusions during four consecutive days. For each patient, approximately 20 plasma samples were available per course. Concentrations of CP, 4OHCP, TT and T were determined using GC and HPLC. Kinetic data were processed using NONMEM.

RESULTS

The pharmacokinetics of TT and T were described with a two-compartment model. TT was eliminated through a non-inducible and an inducible pathway, the latter resulting information of T (ClindTT = 12.4 l/hr, ClnonindTT = 17.0 l/hr). Induction of TT metabolism was mediated by a hypothetical amount of enzyme, different from that involved in CP induction, whose amount increased with time in the presence of CP. The amount of enzyme followed a zero-order formation and a decrease with a first-order elimination rate constant of 0.0343 hr(-1) (t1/2 = 20 hr). This model was significantly better than a model lacking the induction by CP. The model was successfully incorporated into the previously published pharmacokinetic model for CP, and resulted in comparable parameter estimates for this compound and its metabolite 4OHCP.

CONCLUSION

The pharmacokinetics of TT, when administered in combination with CP, were successfully described. The model confirms induction of TT metabolism with time and it appears likely that CP is responsible for this phenomenon. The existence of a mutual pharmacokinetic interaction between CP and TT, as described in our integrated model, may be relevant in clinical practice.

Effect of mycophenolate mofetil on the pharmacokinetics of antiretroviral drugs and on intracellular nucleoside triphosphate pools

OBJECTIVE

To study the effect of mycophenolate mofetil therapy on the pharmacokinetic parameters of a number of antiretroviral drugs, on intracellular pools of deoxycytidine triphosphate (dCTP) and deoxyguanosine triphosphate (dGTP), and on intracellular concentrations of the triphosphate of lamivudine (3TCTP).

DESIGN

Randomised pharmacokinetic study.

PARTICIPANTS

Nineteen HIV-1-infected patients.

METHODS

Antiretroviral-naive men starting treatment with didanosine 400 mg once daily, lamivudine 150 mg twice daily, abacavir 300 mg twice daily, indinavir 800 mg twice daily, ritonavir 100 mg twice daily and nevirapine 200 mg twice daily were randomised to a group with or without mycophenolate mofetil 500 mg twice daily. After 8 weeks of therapy, the plasma pharmacokinetic profiles of mycophenolic acid (the active metabolite of mycophenolate mofetil), abacavir, indinavir and nevirapine, and triphosphate concentrations (dCTP, dGTP and 3TCTP) in peripheral blood mononuclear cells, were determined.

RESULTS

Nine of the 19 patients received mycophenolate mofetil. There was no difference in plasma clearance of indinavir or abacavir between the two groups. The clearance of nevirapine was higher in patients using mycophenolate mofetil (p = 0.04). In 12 patients, of whom five also received mycophenolate mofetil, intracellular triphosphates were measured. There was no significant difference in intracellular dCTP, dGTP or 3TCTP concentrations between the two groups.

CONCLUSION

In this small cohort of patients, mycophenolate mofetil therapy reduced the plasma concentration of nevirapine but had no effect on plasma concentrations of indinavir and abacavir. There were no consistent effects of mycophenolic acid on the intracellular concentrations of dCTP, dGTP or 3TCTP.

Liquid chromatographic assay for the protease inhibitor atazanavir in plasma

Atazanavir is the most recently introduced protease inhibitor for the suppression of the anti-human immunodeficiency virus. A sensitive and selective reversed-phase liquid chromatographic assay for this drug in human plasma has been developed and validated. Atazanavir was isolated from a 500 microL plasma sample using liquid-liquid extraction with dichloromethane. After evaporation and reconstitution of the extract the sample was analysed using liquid chromatography and ultraviolet detection at 280 nm. In the evaluated concentration range (44-4395 ng/mL atazanavir), intra-day precisions were < or =7% and inter-day precisions were < or =14%. Accuracies between 96 and 106% were found. The lower limit of quantification was 44 ng/mL with an intra-day precision of 7%, an inter-day precision of 14% and an accuracy of 87%. There was no interference from 32 tested potentially co-administrated drugs and metabolites. The usefulness of the assay was demonstrated for samples obtained from an HIV-infected patient treated with atazanavir.

Nevirapine and efavirenz pharmacokinetics and covariate analysis in the 2NN study

OBJECTIVE

The aim of this 2NN pharmacokinetic substudy was to investigate the population pharmacokinetics of nevirapine and efavirenz.

METHODS

Treatment-naive, HIV-1-infected patients received nevirapine (once or twice daily), efavirenz or a combination with lamivudine and stavudine. Blood samples were collected on day 3 and weeks 1, 2, 4, 24 and 48. Using non-linear mixed effects modelling, pharmacokinetics of nevirapine and efavirenz and factors involved in the inter-individual variability were investigated.

RESULTS

Clearance of nevirapine in the induction phase (<14 days) and at steady state (>28 days) were 2.02 I/h and 2.81 I/h, respectively. Volume of distribution and absorption rate constant were 77.0 l and 1.66 h(-1), respectively. Clearance of nevirapine was lower in females (13.8%) and in patients with hepatitis B (19.5%). Patients from South America and Western countries had higher clearance of nevirapine compared with Thai and South African patients. The clearances of efavirenz in the induction phase and at steady state were 7.95 l/h and 8.82 l/h, respectively. The volume of distribution and absorption rate constant were 4181 and 0.287 h(-1), respectively. Concomitant use of nevirapine increased clearance of efavirenz (43%). Patients from Thailand had lower clearance than the rest of the population.

CONCLUSIONS

The population pharmacokinetics of nevirapine and efavirenz were assessed in the 2NN trial. For both drugs, an induction phase was distinguished from the steady-state phase. Gender, hepatitis B and geographical region were involved in the variability of the pharmacokinetics of nevirapine. Region and concomitantly used nevirapine were determinants of the pharmacokinetics of efavirenz.

Should Non-Nucleoside Reverse Transcriptase Inhibitors be Combined?

In the treatment of HIV-infected patients, an urgent need exists for more conveniently dosed and better tolerated regimens with improved virological and immunological efficacy. Based on preclinical studies, the combination of two non-nucleoside reverse transcriptase inhibitors (NNRTIs) was considered to fulfill this. Several clinical studies, however, have shown different results with regard to mechanism of action, pharmacokinetics, efficacy and toxicity of dual NNRTI regimens. Combinations of two NNRTIs have shown additive or synergistic inhibitory effects on the HIV-1 reverse transcriptase activity and the viral replication of HIV-1 in vitro, although antagonistic effects have also been described. When nevirapine and efavirenz were administered in combination, the exposure to efavirenz was decreased due to induction of metabolism by nevirapine. When compared with single NNRTI regimens, dual NNRTI regimens showed similar but not superior results with regard to virological and immunological success in treatment-naive and pretreated HIV-1-infected patients. However, NNRTI-associated adverse events, such as clinical hepatitis, elevated liver enzymes, rash, central nervous system toxicity and psychiatric disorders, occurred more frequently when two NNRTIs were administered concomitantly. In conclusion, regimens with both nevirapine and efavirenz seem to result in similar antiviral and immunological efficacy with an increased incidence of adverse events compared with single NNRTI regimens. The combination of two NNRTIs is therefore less desirable than other available and effective treatment options.

Individualised Cancer Chemotherapy: Strategies and Performance of Prospective Studies on Therapeutic Drug Monitoring with Dose Adaptation

Therapeutic drug monitoring (TDM) is increasingly used in clinical practice for the optimisation of drug treatment. Although pharmacokinetic variability is an established factor involved in the variation of therapeutic outcome of many chemotherapeutic agents, the use of TDM in the field of oncology has been limited thus far. An important reason for this is that a therapeutic index for most anticancer agents has not been established; however, in the last 20 years, relationships between plasma drug concentrations and clinical outcome have been defined for various chemotherapeutic agents. Several attempts have been made to use these relationships for optimising the administration of chemotherapeutics by applying pharmacokinetically guided dosage. These prospective studies, individualising chemotherapy dose during therapy based on measured drug concentrations, are discussed in this review. We focus on the way a target value is defined, the methodologies used for dose adaptation and the way the performance of the dose-adaptation approach is evaluated. Furthermore, attention is paid to the results of the studies and the applicability of the strategies in clinical practice. It can be concluded that TDM may contribute to improving cancer chemotherapy in terms of patient outcome and survival and should therefore be further investigated.

Population Pharmacokinetics of Caffeine and its Metabolites Theobromine, Paraxanthine and Theophylline after Inhalation in Combination with Diacetylmorphine

The stimulant effect of caffeine, as an additive in diacetylmorphine preparations for study purposes, may interfere with the pharmacodynamic effects of diacetylmorphine. In order to obtain insight into the pharmacology of caffeine after inhalation in heroin users, the pharmacokinetics of caffeine and its dimethylxanthine metabolites were studied. The objectives were to establish the population pharmacokinetics under these exceptional circumstances and to compare the results to published data regarding intravenous and oral administration in healthy volunteers. Diacetylmorphine preparations containing 100 mg of caffeine were used by 10 persons by inhalation. Plasma concentrations of caffeine, theobromine, paraxanthine and theophylline were measured by high performance liquid chromatography. Non-linear mixed effects modelling was used to estimate population pharmacokinetic parameters. The model was evaluated by the jack-knife procedure. Caffeine was rapidly and effectively absorbed after inhalation. Population pharmacokinetics of caffeine and its dimethylxanthine metabolites could adequately and simultaneously be described by a linear multi-compartment model. The volume of distribution for the central compartment was estimated to be 45.7 l and the apparent elimination rate constant of caffeine at 8 hr after inhalation was 0.150 hr(-1) for a typical individual. The bioavailability was approximately 60%. The presented model adequately describes the population pharmacokinetics of caffeine and its dimethylxanthine metabolites after inhalation of the caffeine sublimate of a 100 mg tablet. Validation proved the stability of the model. Pharmacokinetics of caffeine after inhalation and intravenous administration are to a large extent similar. The bioavailability of inhaled caffeine is approximately 60% in experienced smokers.

Accuracy, feasibility, and clinical impact of prospective Bayesian pharmacokinetically guided dosing of cyclophosphamide, thiotepa, and carboplatin in high-dose chemotherapy

PURPOSE

Relationships between toxicity and pharmacokinetics have been shown for cyclophosphamide, thiotepa, and carboplatin (CTC) in high-dose chemotherapy. We prospectively evaluated whether variability in exposure to CTC and their activated metabolites can be decreased with pharmacokinetically guided dose administration and evaluated its clinical effect.

EXPERIMENTAL DESIGN

Patients received multiple 4-day courses of cyclophosphamide (1,000-1,500 mg/m2/d), thiotepa (80-120 mg/m2/d), and carbop latin (area under the plasma concentration-time curve 3.3-5 mg x min/mL/d). Doses were adapted on day 3 based on pharmacokinetic analyses of cyclophosphamide, 4-hydroxycyclophosphamide, thiotepa, tepa, and carboplatin done on day 1 using a Bayesian algorithm. Doses were also adjusted before and during second and third courses. Observed toxicity was compared with that in patients receiving standard dose CTC (n = 43).

RESULTS

A total of 46 patients (108 courses) were included. For cyclophosphamide, thiotepa, and carboplatin, a total of 39, 58, and 65 dose adaptations were done within courses and 17, 40, and 43 before courses. The precision within which the target exposure was reached improved compared with no adaptation, especially after within-course adaptations (precision for cyclophosphamide, thiotepa, and carboplatin is 19%, 16%, and 13%, respectively); >85% led to an exposure within +/-25% of the target compared with 60% without dose adjustments. Toxicity was similar to that in a reference population, although the incidence of veno-occlusive disease was reduced.

CONCLUSIONS

Bayesian pharmacokinetically guided dosing for CTC was feasible and led to a marked reduction in variability of exposure.

Population Pharmacokinetics of Efavirenz in an Unselected Cohort of HIV-1-Infected Individuals

OBJECTIVE

The aim of this study was to characterise the population pharmacokinetics of efavirenz in a representative patient population and to identify patient characteristics influencing the pharmacokinetics of efavirenz, with the ultimate goal of further developing techniques that can be applied to optimise therapeutic drug monitoring of antiretroviral agents.

METHODS

Ambulatory HIV-1-infected patients using an efavirenz-containing regimen were included. During regular visits, blood samples were collected for efavirenz plasma concentrations and clinical chemistry parameters. Concentrations of efavirenz were quantitatively assessed by a validated high-performance liquid chromatographic with ultraviolet detection method. Using nonlinear mixed-effect modelling (NONMEM), the pharmacokinetics of efavirenz were described. Disposition of efavirenz was described by a two-compartment model and absorption was modelled using a chain of three transition compartments. Apparent clearance (CL/F), volume of distribution after oral administration (V(d)/F), intercompartmental clearance, the peripheral volume of distribution and the intercompartmental transition rate constant (k(tr)) were estimated. Furthermore, interindividual, interoccasion and residual variability were estimated. The influence of patient characteristics on the pharmacokinetic parameters of efavirenz was explored.

RESULTS

From 172 patients, 40 full pharmacokinetic curves and 315 efavirenz plasma concentrations at a single timepoint were available, resulting in a database of 1009 efavirenz plasma concentrations. CL/F, V(d)/F, and k(tr) were 11.7 L/h (4.3% relative standard error [RSE]), 189L (14.6% RSE) and 3.07 h(-1) (11.2% RSE), respectively. Residual variability in the model was composed of 0.14 mg/L additive error and 8.85% proportional error. Asian race and baseline total bilirubin (TBR) increased the relative bioavailability of efavirenz by 56% and 57%, respectively. No significant covariates were found for CL/F or V(d)/F.

CONCLUSION

The pharmacokinetic parameters of efavirenz were adequately described with the developed population pharmacokinetic model. Asian race and baseline TBR were found to be significantly correlated with the bioavailability of efavirenz. The described model will be an essential tool in further optimisation of efavirenz-containing antiretroviral therapy, e.g. by the use of Bayesian estimation of individual pharmacokinetic parameters.

Are adverse events of nevirapine and efavirenz related to plasma concentrations?

OBJECTIVE

The relationships between adverse events (AEs) and plasma concentrations of nevirapine (NVP) and efavirenz (EFV) were investigated as part of the large, international, randomized 2NN study.

METHODS

Treatment-naive, HIV-1-infected patients received NVP (once or twice daily), EFV or their combination, each in combination with lamivudine and stavudine. Blood samples were collected on day 3 and weeks 1, 2, 4, 24 and 48. Concentrations of NVP and EFV were quantitatively assessed by a validated HPLC assay. Individual Bayesian estimates of the area under the plasma concentration-time curve over 24 h (AUC24h), and minimum and maximum plasma concentrations (Cmin and Cmax) as measures for drug exposure of NVP and EFV, were generated using a previously developed population pharmacokinetic model. Pharmacokinetic parameters were compared for patients with and without central nervous system (CNS) and psychiatric AEs, hepatic events, liver enzyme elevations (LEEs) and rash. Furthermore, it was investigated whether a clear cut-off for a pharmacokinetic parameter could be identified above which the incidence of AEs was clearly increased. AEs were also related to demographic parameters and baseline characteristics.

RESULTS

In total, from 1077 patients, NVP (3024 samples) and EFV (1694 samples) plasma concentrations and AE data (825 observations) were available. For all patients Cmin, Cmax and AUC24h were determined. When corrected for known covariates of gender, CD4 cell count at baseline, region, hepatitis coinfection and possible interactions between these factors, no significant associations between AEs and any tested exposure parameter of NVP was observed. Also, no target Cmin value, above which patients were at increased risk for AEs, could be established. On the other hand, geographical region, hepatitis coinfection, CD4 cell count and gender were found to be significantly related with the incidence of CNS and psychiatric AEs, hepatic events, LEEs and rash during the treatment with NVP. The occurrence of elevated liver enzymes during the first 6 weeks in the EFV-containing arm was significantly (P = 0.036) correlated to the exposure of EFV (Cmin). Only hepatitis coinfection impacted on LEEs during the first 6 weeks of treatment. With an EFV Cmin above 2.18 mg/l during the induction phase, patients were 4.4 (range 1.3-15.5) times more at risk for elevated liver enzymes. No other correlations between AEs and EFV pharmacokinetics or patient characteristics could be identified.

CONCLUSIONS

Pharmacokinetic parameters of NVP did not have a relationship to AEs in the 2NN trial when corrected for known covariates. The value of periodical drug monitoring of NVP as a way to prevent toxicity is therefore limited. Treating physicians should instead focus on factors that are more predictive of AEs (gender, CD4 count and hepatitis coinfection). High EFV Cmin levels resulted in elevated liver enzyme values during the first 6 weeks of treatment. Regular measurement of EFV levels and liver enzymes at the start of therapy may therefore be advised.

The plasma and intracellular steady-state pharmacokinetics of lopinavir/ritonavir in HIV-1-infected patients

Therapeutic drug monitoring of protease inhibitors (PIs) is usually performed on plasma samples although their antiretroviral effect takes place inside cells. Little is known, however, about the intracellular accumulation and related plasma pharmacokinetics of PIs such as lopinavir/ritonavir (LPV/RTV). Therefore, we studied the plasma and intracellular (cell-associated) steady-state pharmacokinetics of this PI combination in a dosage of 400/100 mg twice daily in a non-randomized cohort of HIV-1-infected individuals. Plasma (0-12 h) and peripheral blood mononuclear cell (PBMC; 0-8 h) samples were drawn during a 12-h dosing interval in 11 subjects. The plasma concentrations versus time curves of LPV and RTV were characterized by an irregular absorption phase showing double-peaks (Cmax) in most subjects and single-peaks in the remaining patients between 1 and 3 h after drug intake. Pre-dose concentrations of both agents in plasma were significantly higher than the concentrations at the end of the dosing interval indicating the presence of a circadian rhythm in their pharmacokinetics. The course of the intracellular concentrations versus time curves appeared to be similar to the plasma concentration curves, with the highest intracellular concentration measured 3 h after drug intake. The intracellular RTV concentrations were higher than reported in vitro EC50 values and might therefore contribute to the antiretroviral effect of LPV/RTV. The median intracellular-to-plasma concentration ratios (interquartile range) were 1.18 (0.74-2.06) and 4.59 (3.20-7.70) for LPV and RTV, respectively. In conclusion, both LPV and RTV accumulate to potential therapeutic concentrations in PBMCs. Irregular absorption and circadian plasma clearance patterns were observed for the PI combination LPV/RTV.

Race Is Not Associated with Nevirapine Pharmacokinetics

The effect of race on the pharmacokinetics of nevirapine was investigated in a nonselected population. Included patients were ambulatory HIV-1-infected patients from the outpatient clinics of the Academic Medical Center and the Slotervaart Hospital, Amsterdam, The Netherlands. All patients were using nevirapine as part of their antiretroviral regimen and had at least one plasma concentration available for analysis. From the included patients, gender, age, race, hepatitis C status, baseline ASAT value, and body weight were obtained. The nonlinear mixed-effect modeling program (NONMEM) version V 1.1 was used for all analyses. Population pharmacokinetic parameters [clearance (CL/F), volume of distribution (V/F), absorption rate constant (ka)] and interindividual (IIV) and interoccasion variability (IOV) were estimated. The influence of race on the CL/F of nevirapine was tested as Negroid race versus the other races, Asian race versus the other races, and the Negroid and the Asian races as separate variables versus the Caucasian race. A database of 1732 nevirapine plasma concentrations of 383 HIV-1-infected individuals collected during 1186 outpatient clinic visits was available for this analysis. The conclusion of this study is that race is not associated with the pharmacokinetics of nevirapine, and thus requires no dose adaptations.

Low nevirapine plasma concentrations predict virological failure in an unselected HIV-1-infected population

OBJECTIVE

To assess the relationship between plasma nevirapine concentrations and plasma HIV-1 RNA response in HIV-1-infected patients.

DESIGN

An observational cohort analysis.

METHODS

Plasma samples were obtained on a routine basis from 189 patients receiving nevirapine 200mg twice daily, and plasma nevirapine concentrations were measured with reversed phase high performance liquid chromatography. Patients were divided into two groups based on plasma nevirapine concentrations below (and equal to) or above 3 mg/L. The association between steady-state nevirapine concentrations and plasma HIV-1 RNA was determined by multivariate analysis.

RESULTS

Out of 189 patients, 13 (7%) had low nevirapine plasma concentrations and 176 patients had concentrations above 3 mg/L. In total, 22 (12%) patients showed virological failure and 8 patients (4%) discontinued nevirapine because of adverse effects. The risk of failure in patients with nevirapine plasma concentrations </=3mg/L was increased (relative risk 5.0, 95% CI 1.8-13.7). Rashes and liver enzyme elevations each occurred in 8% of patients.

CONCLUSIONS

Low nevirapine drug concentrations are predictive of virological failure.

Simultaneous quantification of the new HIV protease inhibitors atazanavir and tipranavir in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

We have developed and validated an assay, using liquid chromatography coupled with electrospray tandem mass spectrometry (LC-MS/MS), for the quantification of the novel protease inhibitors (PIs) atazanavir and tipranavir. The sample pre-treatment consisted of protein precipitation with a mixture of methanol and acetronitrile using 100 microl plasma for atazanavir and 50 microl for tipranavir. Chromatographic separation was achieved on an Inertsil ODS3 column (50 mm x 2.0 mm i.d., particle size 5 microm), with a quick stepwise gradient using an acetate buffer (pH 5) and methanol, at a flow rate of 0.5 ml/min. The analytical run time was 5.5 min. The triple quadrupole mass spectrometer operated in the positive ion-mode and multiple reaction monitoring (MRM) was used for drug quantification. The assay was linear over a concentration range of 0.05-10 microg/ml for atazanavir and 0.1-75 microg/ml for tipranavir. Saquinavir-d5 was used as internal standard. The intra- and inter-day coefficients of variation were less than 3.8% for atazanavir and less than 10.4% for tipranavir. Accuracies were within +/-7.3 and +/-7.2% for atazanavir and tipranavir, respectively. Both drugs were stable under various relevant storage conditions. The validated concentration ranges proved to be adequate to measure concentrations of human immunodeficiency virus type-1 (HIV-1)-infected individuals. The developed method could easily be combined with a previously developed LC-MS/MS assay for the quantification of protease inhibitors.

Drug‐Drug Interaction between Itraconazole and the Antiretroviral Drug Lopinavir/Ritonavir in an HIV‐1–Infected Patient with Disseminated Histoplasmosis

We describe a drug-drug interaction between coformulated lopinavir/ritonavir and itraconazole in a patient infected with human immunodeficiency virus type 1 who had disseminated histoplasmosis. Coadministration of these agents led to a strong increase in itraconazole concentrations and a decrease in concentrations of its metabolite, hydroxyitraconazole, which is equally active pharmacologically. The dosage of itraconazole was reduced when it was used in combination with lopinavir/ritonavir.

Bayesian Pharmacokinetically Guided Dosing of Paclitaxel in Patients with Non-Small Cell Lung Cancer

PURPOSE

Paclitaxel is a taxane derivative with a profound antitumor activity against a variety of solid tumors. In a previous clinical study in patients with non-small cell lung cancer (NSCLC) treated with paclitaxel, it was shown that paclitaxel plasma concentrations of 0.1 micro mol/liter for > or = 15 h were associated with prolonged survival. The purpose of this study was to evaluate the feasibility of Bayesian dose individualization to attain paclitaxel plasma concentrations >0.1 micromol/liter for > or = 15 h.

EXPERIMENTAL DESIGN

Patients with stage IIIb-IV NSCLC were treated with paclitaxel and carboplatin once every 3 weeks for a maximum of six courses. During the first course, a standard paclitaxel dose of 175 mg/m(2) was administered i.v. in 3 h. In subsequent courses, the paclitaxel dose was individualized based on observed paclitaxel concentrations in plasma during the previous course(s) using a Bayesian algorithm. The paclitaxel dose of a subsequent course was increased to the lowest dose for which the predicted time period during which the paclitaxel plasma concentration exceeds 0.1 micromol/liter was >15 h.

RESULTS

A total of 25 patients have been included in the study (92 evaluable courses). During the first course, the median time period above the threshold concentration was 16.3 h (range, 7.6-31.6 h), and was <15 h for 9 patients (36%). During subsequent individualized courses, the time period above the threshold concentration was <15 h in 23% (5 of 22), 14% (2 of 14), 23% (3 of 13), 11% (1 of 9), and 11% (1 of 9) of the patients in the second, third, fourth, fifth, and sixth course, respectively. Dose increments, ranging from 5 to 65 mg/m(2), were performed in 29 of the 67 individualized courses. Patients with increased individualized doses had similar regimen related toxicities compared with those remaining at a dose of 175 mg/m(2). Toxicity was reversible and manageable, and was mainly hematological (granulocytopenia CTC grade 3/4 in 80% of the patients). The objective response rate was 20%.

CONCLUSIONS

The results indicate that the applied pharmacokinetically guided dosing strategy for paclitaxel is safe and technically feasible. A randomized study is necessary to demonstrate whether dose individualization may result in improved activity and efficacy in patients with NSCLC.

Evaluation of clinical pharmacist interventions on drug interactions in outpatient pharmaceutical HIV-care

OBJECTIVE

To evaluate the usefulness of intervention in drug interactions of antiretroviral drugs with coadministered agents by a clinical pharmacist in outpatient HIV-treatment.

METHODS

The study design included two intervention arms (A and B), which were both preceded by a control observation period. In arm A, a complete list of the currently used drugs, extracted from pharmacy records was provided to the treating physician. In arm B the same list was provided but with a notification when a drug interaction was present and an advice how to handle this. The infectious disease specialist obtained the information before the patient's visit to the outpatient clinic (time point 0). Three months prior (time point -3) and 3 months after (time point +3) the intervention, pharmacy records were also screened for drug interactions. The number of drug interactions (total and per patient) was determined at the three different time points (-3, 0, +3). In addition, drug interactions encountered at time points -3 and 0 were checked for their presence at time points 0 and +3, respectively, for both intervention arms.

RESULTS

Arms A and B included 115 and 105 patients, respectively. Patient characteristics of both intervention arms were similar at time point 0. The number of interactions and the number of patients with interactions were similar in both intervention arms at time point 0. There were 42 and 40 potential drug interactions in 30 and 24 patients in arms A and B, respectively. The reduction in the number of interactions per patient over time and after intervention was small but significant, and was equal in both intervention arms. The advice of the clinical pharmacist had thus no additional value.

CONCLUSION

Both interventions were effective in reducing the number of drug interactions per patient. The advice of a clinical pharmacist was, however, redundant in the studied setting.

Simultaneous quantification of cyclophosphamide, 4-hydroxycyclophosphamide, N,N',N"-triethylenethiophosphoramide (thiotepa) and N,N',N"-triethylenephosphoramide (tepa) in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

The alkylating agents cyclophosphamide (CP) and N, N', N"-triethylenethiophosphoramide (thiotepa) are often co-administered in high-dose chemotherapy regimens. Since these regimens can be complicated by the occurrence of severe and sometimes life-threatening toxicities, pharmacokinetically guided administration of these compounds, to reduce variability in exposure, may lead to improved tolerability. For rapid dose adaptations during a chemotherapy course, we have developed and validated an assay, using liquid chromatography coupled with electrospray tandem mass spectrometry (LC/MS/MS), for the routine quantification of CP, thiotepa and their respective active metabolites 4-hydroxycyclophosphamide (4OHCP) and N, N', N"-triethylenephosphoramide (tepa) in plasma. Because of the instability of 4OHCP in plasma, the compound is derivatized with semicarbazide (SCZ) immediately after sample collection and quantified as 4OHCP-SCZ. Sample pretreatment consisted of protein precipitation with a mixture of methanol and acetronitrile using 100 microl of plasma. Chromatographic separation was performed on an Zorbax Extend C18 column (150 x 2.1 mm i.d., particle size 5 microm), with a quick gradient using 1 mM ammonia solution and acetonitrile, at a flow-rate of 0.4 ml min(-1). The analytical run time was 10 min. The triple quadrupole mass spectrometer was operating in the positive ion mode and multiple reaction monitoring was used for drug quantification. The method was validated over the concentration ranges 200-40,000 ng ml(-1) for CP, 50-5000 ng ml(-1) for 4OHCP-SCZ and 5-2500 ng ml(-1) for thiotepa and tepa, using 100 microl of human plasma. These dynamic concentration ranges proved to be relevant in daily practice. Hexamethylphosphoramide was used as an internal standard. The coefficients of variation were <12% for both intra-day and inter-day precisions for each compound. Mean accuracies were also between the designated limits (+/- 15%). This robust and rapid LC/MS/MS assay is now successfully applied for routine therapeutic drug monitoring of CP, thiotepa and their metabolites in our hospital.

Photophobia in a patient with high indinavir plasma concentrations

An HIV-infected male patient experienced photophobia after a change in dosing regimen that resulted in substantially higher indinavir plasma levels as compared with a reference population. High indinavir levels were suspected to be the cause of photophobia in this patient.

Incidence and risk factors for nevirapine-associated rash

OBJECTIVE

To determine the incidence of rash in HIV-1 infected individuals starting a nevirapine-containing regimen in an unselected outpatient clinic population. Possible risk factors including plasma concentrations of nevirapine were evaluated for their relationship with the occurrence of a rash.

METHODS

The occurrence of rash was extracted from the outpatient medical records or based on a prescription of the antihistaminic cetirizine as documented by the community pharmacy within the first 90 days of nevirapine use. During regular visits to the clinic blood samples were collected for the determination of nevirapine plasma concentrations. Possible risk factors such as demographics, immunology, virology, clinical chemistry and antiretroviral pretreatment were collected at baseline for each patient. In addition, concomitantly used drugs during the nevirapine-based regimen were recorded. The association between these factors and the occurrence of rash was studied. Primary outcome was the onset of rash within the first 90 days after initiation of a nevirapine-containing regimen.

RESULTS

Data from 216 HIV-1-infected patients were used in this study. Thirty-eight patients (17.6%) developed a rash of some grade that led to discontinuation of nevirapine in seven patients (3.2% of the included patients). The median time to occurrence of rash was 26 days (interquartile range 17-46 days). The multivariate analysis showed that patients pretreated with antiretroviral drugs less than 12 months before the initiation of a nevirapine-containing regimen had a more than 2.5-fold increased risk of developing rash. Furthermore, nevirapine plasma concentrations were also significantly related to the occurrence of rash. A more than twofold increased risk for developing rash was observed for patients with nevirapine plasma concentrations above 5.3 mg/l.

CONCLUSIONS

This is the first study demonstrating that patients with antiretroviral pretreatment less than 12 months and with nevirapine plasma concentrations above 5.3 mg/l during the first 90 days of treatment are at a higher risk for the development of rash. It is therefore advised to monitor this group of patients carefully when initiating nevirapine-containing therapy.

Simple and rapid method for the simultaneous determination of the non-nucleoside reverse transcriptase inhibitors efavirenz and nevirapine in human plasma using liquid chromatography

Efavirenz and nevirapine are non-nucleoside reverse transcriptase inhibitors for the treatment of HIV-1-infected individuals. A simple and rapid high-performance liquid chromatographic method for the simultaneous quantification of efavirenz and nevirapine in human plasma suitable for therapeutic drug monitoring is described. Sample pre-treatment consisted of protein precipitation with acetonitrile and subsequently dilution with distilled water. The drugs were separated from endogenous compounds by isocratic reversed-phase high-performance liquid chromatography with ultraviolet detection at 275 nm. The method was validated over the therapeutically relevant concentration range of 0.05-15.0 mg l(-1) and 0.25-15.0 mg l(-1) for efavirenz and nevirapine, respectively, using a volume of 100 microl of plasma. The calibration curves were linear over this concentration range. Carbamazepine was used as internal standard. The assay proved to be accurate (accuracies varied between -12.7 and 8.5%) and precise (intra- and inter-assay precisions were less then 5.9%). The tested batches of control human plasma and frequently co-administered drugs did not interfere with the described methodology. Efavirenz and nevirapine were stable under various relevant storage conditions. This validated assay is suited for use in pharmacokinetic studies with efavirenz and nevirapine and can readily be implemented in the setting of a hospital laboratory for the monitoring of efavirenz and nevirapine concentrations.