In vivo pharmacokinetics and pharmacodynamics of a new triazole, voriconazole, in a murine candidiasis model

Determination of saliva trough levels for monitoring voriconazole therapy in immunocompromised children and adults

To evaluate the reliability and practical use of saliva for therapeutic drug monitoring of the antifungal agent voriconazole in immunocompromised patients, a paired-sample study was conducted. Plasma and saliva trough levels were measured in seven children and nine adults who required treatment for the prevention or therapy of systemic fungal infections. The pediatric patients received a voriconazole dosage of 7 mg/kg intravenously twice a day. Adults were treated with two loading doses of 6 mg/kg intravenously followed by a maintenance dose of 4 mg/kg intravenously twice a day. Based on 104 paired plasma/saliva specimens, we found a significant correlation between the voriconazole concentrations in blood and saliva (r > 0.95). The median saliva/plasma voriconazole concentration ratio was 0.34 in children and 0.40 in adults. Intra- and interpatient variability in the saliva/plasma ratios were 22% and 23% in children and 16% and 24% in adults, respectively. Thirty-three percent of plasma trough levels were below 1.0 microg/mL or above 6.0 microg/mL and occurred in six pediatric and four adult patients. Monitoring of salivary concentrations proved to be a realistic alternative in patients when blood drawing is difficult. Especially in therapeutic drug monitoring, an easier sample collection being noninvasive and painless is more acceptable to patients, particularly children.

Impact of cyp51A mutations on the pharmacokinetic and pharmacodynamic properties of voriconazole in a murine model of disseminated aspergillosis

The in vivo efficacy of voriconazole against 4 clinical Aspergillus fumigatus isolates with MICs ranging from 0.125 to 2 mg/liter (CLSI document M38A) was assessed in a nonneutropenic murine model of disseminated aspergillosis. The study involved TR/L98H, M220I, and G54W mutants and a wild-type control isolate. Oral voriconazole therapy was started 24 h after intravenous infection of mice and was given once daily for 14 consecutive days, with doses ranging from 10 to 80 mg/kg of body weight, using survival as the endpoint. Survival for all isolates was dependent on the voriconazole dose level (R(2) value of 0.5 to 0.6), but a better relationship existed for the area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC/MIC ratio) or the AUC for the free, unbound fraction of the drug divided by the MIC (fAUC/MIC ratio) (R(2) value of 0.95 to 0.98). The 24-h fAUC/MIC ratio showed a clear relationship to effect, with an exposure index for amount of free drug required for 50% of maximum effectiveness (fEI(50)) of 11.17 at day 7. Maximum effect was reached at values of around 80 to 100, comparable to that observed for posaconazole and A. fumigatus. Mice infected with an isolate having a MIC of 2 mg/liter required an exposure that was inversely correlated with the increase in MIC compared to that of the wild-type control, but due to nonlinear pharmacokinetics, this required only doubling of the voriconazole dose. The efficacy of voriconazole for isolates with high MICs for other triazoles but voriconazole MICs within the wild-type population range was comparable to that for the wild-type control. Finally, we used a grapefruit juice-free murine model of aspergillosis and concluded that this model is appropriate to study pharmacokinetic/pharmacodynamic relationships of voriconazole.

Bioavailability and population pharmacokinetics of voriconazole in lung transplant recipients

This study was undertaken to characterize the pharmacokinetics and bioavailability of voriconazole in adult lung transplant patients during the early postoperative period, identify factors significantly associated with various pharmacokinetic parameters, and make recommendations for adequate dosing regimens. Thirteen lung transplant patients received two intravenous infusions (6 mg/kg, twice daily [b.i.d.]) immediately posttransplant followed by oral doses (200 mg, b.i.d.) for prophylaxis. Blood samples (9/interval) were collected during one intravenous and one oral dosing interval from each patient. Voriconazole plasma concentrations were measured by high-pressure liquid chromatography (HPLC). NONMEM was used to develop pharmacokinetic models, evaluate covariate relationships, and perform Monte Carlo simulations. There was a good correlation (R(2) = 0.98) between the area under the concentration-time curve specific for the dose evaluated (AUC(0-∞)) and trough concentrations. A two-compartment model adequately described the data. Population estimates of bioavailability, clearance, V(c), and V(p) were 45.9%, 3.45 liters/h, 54.7 liters, and 143 liters. Patients with cystic fibrosis (CF) exhibited a significantly lower bioavailability (23.7%, n = 3) than non-CF patients (63.3%, n = 10). Bioavailability increased with postoperative time and reached steady levels in about 1 week. V(p) increased with body weight. Bioavailability of voriconazole is substantially lower in lung transplant patients than non-transplant subjects but significantly increases with postoperative time. CF patients exhibit significantly lower bioavailability and exposure of voriconazole and therefore need higher doses. Intravenous administration of voriconazole during the first postoperative day followed by oral doses of 200 mg or 400 mg appeared to be the optimal dosing regimen. However, voriconazole levels should be monitored, and the dose should be individualized based on trough concentrations as a good measure of drug exposure.

What is the role of therapeutic drug monitoring in antifungal therapy?

Despite an expanding number of therapeutic options for treating invasive fungal infection (IFI), the mortality rate from these infections remains high. Many risk factors for poor outcome from IFI (eg, the compromised immune status of the host) are not modifiable by the treating clinician. Thus, elevated interest exists in any modifiable factor that might improve outcome. Many of the new antifungal agents have marked variability in drug concentration based on either inconsistent absorption or elimination, leading to very wide interpatient variability. Many agents also have a narrow therapeutic index, meaning a small range between drug levels too low to achieve the desired clinical benefit and high enough to produce unwanted or toxic effects. Therefore, therapeutic drug monitoring is useful to maximize efficacy while minimizing drug toxicity of some antifungal agents.

Development, validation, and routine application of a high-performance liquid chromatography method coupled with a single mass detector for quantification of itraconazole, voriconazole, and posaconazole in human plasma

We have developed and validated a high-performance liquid chromatography method coupled with a mass detector to quantify itraconazole, voriconazole, and posaconazole using quinoxaline as the internal standard. The method involves protein precipitation with acetonitrile. Mean accuracy (percent deviation from the true value) and precision (relative standard deviation percentage) were less than 15%. Mean recovery was more than 80% for all drugs quantified. The lower limit of quantification was 0.031 microg/ml for itraconazole and posaconazole and 0.039 microg/ml for voriconazole. The calibration range tested was from 0.031 to 8 microg/ml for itraconazole and posaconazole and from 0.039 to 10 microg/ml for voriconazole.

In vivo comparison of the pharmacodynamic targets for echinocandin drugs against Candida species

Previous pharmacodynamic studies using in vivo candidiasis models have demonstrated that the 24-h area under the concentration-time curve (AUC)/MIC is a good descriptor of the echinocandin exposure-response relationship. Further studies investigating the 24-h AUC/MIC target for a stasis endpoint identified free-drug 24-h AUC/MIC against Candida albicans and were similar for two echinocandins, anidulafungin and micafungin. The current studies expand investigation of a third echinocandin (caspofungin) and compare the pharmacodynamic target among C. albicans, Candida glabrata, and Candida parapsilosis. Treatment studies were conducted with six C. albicans, nine C. glabrata, and 15 C. parapsilosis strains with various MICs (anidulafungin, 0.015 to 4.0 microg/ml; caspofungin, 0.03 to 4.0 microg/ml; and micafungin, 0.008 to 1.0 microg/ml). Efficacy was closely tied to MIC and the 24-h AUC/MIC. Therapy against C. parapsilosis required more of each echinocandin on a mg/kg basis. Caspofungin required less drug on a mg/kg basis for efficacy against all of the organisms than did the other two drugs. However, the 24-h AUC/MIC targets were similar among the echinocandins when free drug concentrations were considered, suggesting the relevance of protein binding. The targets for C. parapsilosis (mean, 7) and C. glabrata (mean, 7) were significantly lower than those for C. albicans (mean, 20) for each echinocandin. The results suggest that current susceptibility breakpoints and the consideration of organism species in these determinations should be reexplored.

Voriconazole pharmacokinetics and pharmacodynamics in children

BACKGROUND

Voriconazole pharmacokinetic and pharmacodynamic data are lacking in children.

METHODS

Records at the Childrens Hospital Los Angeles were reviewed for children with > or =1 serum voriconazole concentration measured from 1 May 2006 through 1 June 2007. Information on demographic characteristics, dosing histories, serum concentrations, toxicity and survival, and outcomes was obtained.

RESULTS

A total of 207 voriconazole measurements were obtained from 46 patients (age, 0.8-20.5 years). A 2-compartment Michaelis-Menten pharmacokinetic model fit the data best but explained only 80% of the observed variability. The crude mortality rate was 28%, and each trough serum voriconazole concentration <1000 ng/mL was associated with a 2.6-fold increased odds of death (95% confidence interval, 1.6-4.8; P=.002). Serum voriconazole concentrations were not associated with hepatotoxicity. Simulations predicted an intravenous dose of 7 mg/kg or an oral dose of 200 mg twice daily would achieve a trough >1000 ng/mL in most patients, but with a wide range of possible concentrations.

CONCLUSIONS

We found a pharmacodynamic association between a voriconazole trough >1000 ng/mL and survival and marked pharmacokinetic variability, particularly after enteral dosing, justifying the measurement of serum concentrations.

Monitoring plasma voriconazole levels following intravenous administration in critically ill patients: an observational study

Data relating to the pharmacokinetics of voriconazole in critically ill patients are lacking. A prospective observational study was conducted on 18 non-consecutive critically ill patients aged 24-97 years, comprising 12 patients with normal renal function (NRF) [creatinine clearance (CL(Cr)) > or = 60 mL/min] and 6 patients with moderate renal impairment (MRI) (CL(Cr) 40-55 mL/min), administered voriconazole intravenously (6 mg/kg loading dose and 3-4 mg/kg twice daily thereafter) in order to determine the suitability of these doses in this patient population. Steady-state blood levels were monitored and liver and renal function were recorded throughout treatment. Large variability in patient plasma levels was observed, ranging from 37% at < or = 1 mg/L (minimum inhibitory concentration at which, for most fungal pathogens, 90% of isolates are susceptible) to 19% at >5.5mg/L. Moreover, maintaining trough concentrations above clinical breakpoints was not consistently achieved because 16/30 (53%) were < or = 1 mg/L. In a few MRI patients, average concentrations were found to be significantly different compared with those of NRF patients administered the same dose, however this difference was not noted in pharmacokinetic parameters following dose normalisation. None of the patients experienced deterioration in renal or liver function. Recommended voriconazole doses are inadequate to achieve drug concentrations >1 microg/mL over the entire dosing interval in some critically ill patients.

Voriconazole pharmacokinetics in liver transplant recipients

The objective of this study was to evaluate the pharmacokinetics of voriconazole and the potential correlations between pharmacokinetic parameters and patient variables in liver transplant patients on a fixed-dose prophylactic regimen. Multiple blood samples were collected within one dosing interval from 15 patients who were initiated on a prophylactic regimen of voriconazole at 200 mg enterally (tablets) twice daily starting immediately posttransplant. Voriconazole plasma concentrations were measured using high-pressure liquid chromatography (HPLC). Noncompartmental pharmacokinetic analysis was performed to estimate pharmacokinetic parameters. The mean apparent systemic clearance over bioavailability (CL/F), apparent steady-state volume of distribution over bioavailability (Vss/F), and half-life (t1/2) were 5.8+/-5.5 liters/h, 94.5+/-54.9 liters, and 15.7+/-7.0 h, respectively. There was a good correlation between the area under the concentration-time curve from 0 h to infinity (AUC0-infinity) and trough voriconazole plasma concentrations. t1/2, maximum drug concentration in plasma (Cmax), trough level, AUC0-infinity, area under the first moment of the concentration-time curve from 0 h to infinity (AUMC0-infinity), and mean residence time from 0 h to infinity (MRT0-infinity) were significantly correlated with postoperative time. t1/2, lambda, AUC0-infinity, and CL/F were significantly correlated with indices of liver function (aspartate transaminase [AST], total bilirubin, and international normalized ratio [INR]). The Cmax, last concentration in plasma at 12 h (Clast), AUMC0-infinity, and MRT0-infinity were significantly lower in the presence of deficient CYP2C19*2 alleles. Donor characteristics had no significant correlation with any of the pharmacokinetic parameters estimated. A fixed dosing regimen of voriconazole results in a highly variable exposure of voriconazole in liver transplant patients. Given that trough voriconazole concentration is a good measure of drug exposure (AUC), the voriconazole dose can be individualized based on trough concentration measurements in liver transplant patients.

Antifungal pharmacokinetics and pharmacodynamics: bridging from the bench to bedside

This review considers a way in which experimental data can be used to identify safe and effective antifungal regimens for humans. The process begins with experimental models of invasive fungal infections that enable definition of optimal dosages and schedules of antifungal drug administration to be defined. These preclinical models also enable the identification of drug exposure targets that are associated with therapeutic outcomes of interest. Human pharmacokinetic variability results in a considerable range of drug exposures following the use of fixed antifungal drug regimens. This variability can be quantified using population pharmacokinetic modeling techniques. Monte Carlo simulation can then be used to simulate pharmacokinetic variability and thereby estimate the proportion of patients with a therapeutic outcome of interest. Effective and safe regimens can thus be studied appropriately in clinical settings. This approach can, and should, be used to optimize antifungal therapy for a large number of clinical scenarios.

Pharmacokinetics and pharmacodynamics of a novel triazole, isavuconazole: mathematical modeling, importance of tissue concentrations, and impact of immune status on antifungal effect

Isavuconazole is a triazole with broad-spectrum activity against medically important fungal pathogens. We investigated the pharmacokinetics and pharmacodynamics of isavuconazole in a murine model of disseminated candidiasis. We determined the pharmacokinetics in both plasma and kidney. The relationship between tissue concentrations and the resultant antifungal effect was described using a mathematical model. The pharmacodynamic parameter that optimally links drug exposure with the antifungal effect was determined using dose fractionation studies. The impact of the immune status of mice receiving isavuconazole was determined in persistently and temporarily neutropenic animals. The pharmacokinetics of 1.6 to 28 mg isavuconazole/kg of body weight were linear. Exposure-response relationships demonstrated near-maximal effect following the administration of >15 mg/kg. The mathematical model showed that exposures in the kidney were 5.77 times higher than those in plasma, and there was persistence of the drug at this site despite concentrations in plasma falling to undetectable levels. The in vitro and in vivo postantifungal effects were 2 to 5 and 8.41 h, respectively. The area under the concentration-time curve (AUC)/MIC ratio was the parameter that optimally linked drug exposure with the observed antifungal effect. The total drug AUC/MIC ratios associated with a 90% probability of survival in temporarily and persistently neutropenic mice were 270 and 670, respectively. Once corrected for protein binding, these values are similar to the magnitude of drug exposure associated with a high probability of a successful therapeutic outcome for other triazoles. This study provides the experimental foundation for the use of isavuconazole in patients with disseminated candidiasis.

Concentrations of voriconazole in healthy and inflamed lung in rats

By utilizing the microdialysis technique, we investigated the pharmacokinetic profile of voriconazole in the interstitium of the lungs and skeletal muscle tissue of rats after a single intravenous dose under healthy and inflammatory conditions. As expected, voriconazole penetrated excellently into the interstitium of tissues, and its levels were descriptively almost identical to free concentration-versus-time profiles in plasma.

Therapeutic drug monitoring of voriconazole in a child with invasive aspergillosis requiring extracorporeal membrane oxygenation

We describe a patient with invasive pulmonary aspergillosis on extracorporeal membrane oxygenation therapy in which therapeutic drug monitoring and individualization of therapy by measuring voriconazole plasma concentrations were performed.

Combination therapy of advanced invasive pulmonary aspergillosis in transiently neutropenic rats using human pharmacokinetic equivalent doses of voriconazole and anidulafungin

At present, voriconazole (VOR) is the drug of first choice for treating invasive pulmonary aspergillosis (IPA). However, particularly in advanced stages of disease and in the severely immunocompromised host, the mortality remains substantial. The combination of VOR with an echinocandin may improve the therapeutic outcome. We investigate here whether combining VOR and anidulafungin (ANI) in advanced IPA in transiently neutropenic rats results in a higher therapeutic efficacy. Since VOR is metabolized more rapidly in rodents than in humans, dosage adjustment for VOR is necessary to obtain an area under the plasma concentration-time curve (AUC) in rodents that is equivalent to that of humans. In this study, the pharmacokinetics of VOR and ANI in rats were elucidated, and dosage schedules were applied that produced AUCs similar to those of humans. The developed dose schedules were well tolerated by the rats, without effects on renal and hepatic functions. VOR showed excellent efficacy in early IPA (100% rat survival). In advanced IPA, VOR was less efficacious (50% rat survival), whereas a significant decrease in galactomannan concentrations in lungs and sera was found in surviving rats. ANI administered in advanced IPA resulted in 22% rat survival, and the serum concentrations of fungal galactomannan were slightly but not significantly decreased. The addition of ANI to VOR did not result in significantly increased therapeutic efficacy in advanced IPA, resulting in 67% rat survival and a significant decrease in galactomannan concentration in serum. In conclusion, VOR monotherapy is therapeutically effective in the treatment of advanced-stage IPA and superior to the use of ANI. Combining both agents does not significantly improve the therapeutic outcome.

Therapeutic drug monitoring for triazoles

PURPOSE OF REVIEW

Invasive fungal infections are a leading cause of morbidity and mortality in immunocompromised patients, and mechanisms to optimize therapeutic outcomes are urgently required. Therapeutic drug monitoring represents an important component for the routine use of the triazoles.

RECENT FINDINGS

Triazoles have revolutionized the prevention and treatment of invasive fungal infections. Increasing data suggest that this class displays important concentration-effect and concentration-toxicity relationships. There has been an increased understanding of the pharmacokinetics and pharmacodynamics of triazoles, and this has facilitated the identification of concentrations (or drug exposures) that are both effective and nontoxic. This review discusses the application of therapeutic drug monitoring to fluconazole, itraconazole, voriconazole and posaconazole.

SUMMARY

Therapeutic drug monitoring represents an important mechanism to optimize the outcome of immunocompromised patients receiving triazoles.

Therapeutic drug monitoring of voriconazole

Voriconazole is a triazole antifungal developed for the treatment of life-threatening fungal infections in immunocompromised patients. The drug, which is available for both oral and intravenous administration, has broad-spectrum activity against pathogenic yeasts, dimorphic fungi, and opportunistic molds. Voriconazole has a nonlinear pharmacokinetic profile with a wide inter- and intraindividual variety. This variability is caused by many factors such as gender, age, genotypic variation, liver dysfunction, the presence of food, and so on. Another important factor influencing voriconazole's pharmacokinetic profile is drug-drug interactions with CYP450 inhibitors as well as inducers. Variability in plasma concentrations, as a result of the previously mentioned aspects, may lead to variability in efficacy or toxicity. Determination of plasma concentrations is indicated in situations to guide dosing and to individualize and improve the treatment options resulting in better therapeutic outcome or fewer side effects. In this article, we review factors influencing voriconazole pharmacokinetic profile, the data supporting exposure-effect and exposure-toxicity relationships, review the gaps in current knowledge, which make broad recommendations for therapeutic drug monitoring difficult for voriconazole, provide the indications in which therapeutic drug monitoring is reasonable based on currently available data (eg, children), and outline the ways in which this problem could be solved. We provide a summary of the problem so that further research can be conducted to address this are of clinical need.

Free renal levels of voriconazole determined by microdialysis in healthy and Candida sp.-infected Wistar rats

The aims of this study were to evaluate free levels of voriconazole (VCZ) in the kidney of healthy and Candida albicans- or Candida krusei-infected Wistar rats using microdialysis and to establish the relationship between free renal and free plasma levels in both conditions. VCZ (40mg/kg or 60mg/kg) was administered orally (n=6 per group) and blood and microdialysate samples were collected at predetermined time points up to 18h. The mean area under the total concentration-time curve (AUC(0-infinity)) in healthy animals increased from 44.2+/-7.3microg/h/mL to 78.8+/-4.0microg/h/mL for plasma and from 15.1+/-2.4microg/h/mL to 27.9+/-2.6microg/h/mL for tissue after 40mg/kg and 60mg/kg VCZ dosing, respectively, showing non-linear pharmacokinetics described by a one-compartment model with Michaelis-Menten elimination. There were no statistical differences between the AUC(0-infinity) of plasma and tissue for either healthy or infected groups for the same dose. The antifungal tissue penetration was similar for both doses and all conditions investigated (0.34+/-0.06). VCZ protein binding was concentration-independent and was on average 66.0+/-4.0%, allowing the prediction of free renal levels using pharmacokinetic parameters obtained from total plasma fitting. The results showed that VCZ free renal and free plasma levels are similar in healthy rats and in rats with disseminated candidiasis caused by C. albicans or C. krusei. Therefore, plasma free levels can be used to optimise dosing regimens for this drug.

Therapeutic drug monitoring of antifungals: pharmacokinetic and pharmacodynamic considerations

Therapeutic drug monitoring of any pharmacologic agent should be considered when there is both significant pharmacokinetic variability and strong, clinically relevant, exposure-effect relationships. Many antifungal drugs exhibit marked variability in drug concentration as a result of inconsistent absorption, metabolism, elimination, or interaction with concomitant medications. For each of the available antifungal drugs, both preclinical and clinical trials have exhibited a relationship between serum concentrations and treatment efficacy. For a smaller subset of compounds, a similar relationship has been identified for the toxicity. The kinetic variability among patients falls outside the therapeutic window for a group of four antifungal compounds. This review summarizes the current literature on therapeutic drug monitoring for these antifungal agents.

Association of fluconazole pharmacodynamics with mortality in patients with candidemia

Recent studies of nonneutropenic patients with candidemia or candidiasis suggest that fluconazole pharmacodynamic parameters correlate with clinical outcomes; however, additional data of correlation to mortality in patients with candidemia would be valuable. We assessed the impact of MICs for Candida, fluconazole pharmacodynamics, and patient characteristics on all-cause mortality with use of a prospective cohort of 96 hospitalized patients with candidemia. Among 84 patients for whom Candida isolates were available for testing, the most frequent Candida species isolated were Candida albicans (44%), followed by Candida parapsilosis (20.2%), and Candida glabrata (20.2%). Fluconazole resistance (MIC of >or=64 microg/ml) was present in 7 (8.3%) to 10 (11.9%) of 84 isolates, depending on the MIC endpoint determination method (50% or 80% inhibition read at 24 or 48 h). Overall mortality occurred in 27 (28.1%) of 96 patients, and nonsurvivors were more likely to have fluconazole-resistant isolates (25% versus 6.7%; P = 0.02). Multivariable analysis demonstrated an association between fluconazole resistance and mortality, but it did not reach statistical significance (odds ratio, 5.3; 95% confidence interval, 0.8 to 33.4; P = 0.08). By pharmacodynamic analysis, a fluconazole area under the concentration-time curve/MIC of <11.5 or MIC of >or=64 was associated with increased patient mortality (P <or= 0.09). These data support previous findings of an antifungal exposure-response relationship to mortality in patients with candidemia. In addition, similar MICs were obtained using a 24- or 48-h MIC endpoint determination, thus providing the opportunity to assess earlier the impact of isolate susceptibility on therapy.

Assessment of Aspergillus fumigatus burden in pulmonary tissue of guinea pigs by quantitative PCR, galactomannan enzyme immunoassay, and quantitative culture

Early diagnosis of invasive pulmonary aspergillosis is problematic in some patient groups due to the lack of rapid, sensitive, specific, and reliable diagnostic tests. Fungal burden and therapeutic efficacy were assessed by survival, quantitative culture (CFU counts), galactomannan enzyme immunoassay (GM-EIA), and quantitative PCR (qPCR) in a new guinea pig model of invasive pulmonary aspergillosis using an aerosol challenge. At 1 day postinfection, qPCR determined that the pulmonary fungal burden was 2 log(10) higher than that determined by CFU counting and increased significantly (P < 0.03) over time. In contrast, the tissue burden assessed by CFU counting did not rise over the course of the study. Therapy with the antifungal drug voriconazole produced statistically significant decreases in pulmonary fungal burden, as detected by CFU counting (P < 0.02), qPCR, and GM-EIA (both P < 0.0002). Daily assessment of the progression of fungal infection in serum was performed by qPCR and GM-EIA. GM-EIA demonstrated a statistically significant reduction in the fungal load on days 6 and 7 in voriconazole-treated animals compared to time-matched controls (P < 0.02). Confirmation of fungal tissue burden by two or more methods should provide a more precise account of the burden, allowing improved assessment of diagnostic and therapeutic strategies in invasive pulmonary aspergillosis.

Voriconazole therapeutic drug monitoring in patients with invasive mycoses improves efficacy and safety outcomes

BACKGROUND

Voriconazole is the therapy of choice for aspergillosis and a new treatment option for candidiasis. Liver disease, age, genetic polymorphism of the cytochrome CYP2C19, and comedications influence voriconazole metabolism. Large variations in voriconazole pharmacokinetics may be associated with decreased efficacy or with toxicity.

METHODS

This study was conducted to assess the utility of measuring voriconazole blood levels with individualized dose adjustments.

RESULTS

A total of 181 measurements with high-pressure liquid chromatography were performed during 2388 treatment days in 52 patients. A large variability in voriconazole trough blood levels was observed, ranging from <or=1 mg/L (the minimum inhibitory concentration at which, for most fungal pathogens, 90% of isolates are susceptible) in 25% of cases to >5.5 mg/L (a level possibly associated with toxicity) in 31% of cases. Lack of response to therapy was more frequent in patients with voriconazole levels <or=1 mg/L (6 [46%] of 13 patients, including 5 patients with aspergillosis, 4 of whom were treated orally with a median dosage of 6 mg/kg per day) than in those with voriconazole levels >1 mg/L (15 [12%] of 39 patients; P=.02). Blood levels >1 mg/L were reached after increasing the voriconazole dosage, with complete resolution of infection in all 6 cases. Among 16 patients with voriconazole trough blood levels >5.5 mg/L, 5 patients (31%) presented with an encephalopathy, including 4 patients who were treated intravenously with a median voriconazole dosage of 8 mg/kg per day, whereas none of the patients with levels <or=5.5 mg/L presented with neurological toxicity (P=.002). Comedication with omeprazole possibly contributed to voriconazole accumulation in 4 patients. In all cases, discontinuation of therapy resulted in prompt and complete neurological recovery.

CONCLUSIONS

Voriconazole therapeutic drug monitoring improves the efficacy and safety of therapy in severely ill patients with invasive mycoses.

Mucosal damage and neutropenia are required for Candida albicans dissemination

Candida albicans fungemia in cancer patients is thought to develop from initial gastrointestinal (GI) colonization with subsequent translocation into the bloodstream after administration of chemotherapy. It is unclear what components of the innate immune system are necessary for preventing C. albicans dissemination from the GI tract, but we have hypothesized that both neutropenia and GI mucosal damage are critical for allowing widespread invasive C. albicans disease. We investigated these parameters in a mouse model of C. albicans GI colonization that led to systemic spread after administration of immunosuppression and mucosal damage. After depleting resident GI intestinal flora with antibiotic treatment and achieving stable GI colonization levels of C. albicans, it was determined that systemic chemotherapy with cyclophosphamide led to 100% mortality, whereas selective neutrophil depletion, macrophage depletion, lymphopenia or GI mucosal disruption alone resulted in no mortality. Selective neutrophil depletion combined with GI mucosal disruption led to disseminated fungal infection and 100% mortality ensued. GI translocation and dissemination by C. albicans was also dependent on the organism's ability to transform from the yeast to the hyphal form. This mouse model of GI colonization and fungemia is useful for studying factors of innate host immunity needed to prevent invasive C. albicans disease as well as identifying virulence factors that are necessary for fungal GI colonization and dissemination. The model may also prove valuable for evaluating therapies to control C. albicans infections.

A pharmacokinetic/pharmacodynamic mathematical model accurately describes the activity of voriconazole against Candida spp. in vitro

We developed a pharmacokinetic/pharmacodynamic (PK/PD) mathematical model that fits voriconazole time-kill data against Candida isolates in vitro and used the model to simulate the expected kill curves for typical intravenous and oral dosing regimens. A series of Emax mathematical models were used to fit time-kill data for two isolates each of Candida albicans, Candida glabrata and Candida parapsilosis. PK parameters extracted from human data sets were used in the model to simulate kill curves for each isolate. Time-kill data were best fit by using an adapted sigmoidal Emax model that corrected for delays in candidal growth and the onset of voriconazole activity, saturation of the number of Candida and the steepness of the concentration-response curve. The rates of maximal killing by voriconazole (kmax) were highly correlated with the growth rates (ks) of the isolates (Pearson's correlation coefficient=0.9861). Simulations using PK parameters derived from the human data sets showed fungistatic effects against each of the isolates. In conclusion, we demonstrated that the activity of voriconazole against Candida isolates can be accurately described using a mathematical model. In the future, it might be possible to devise optimal dosing regimens of voriconazole using the model and PK data collected in vivo.

Mechanism-based pharmacokinetic-pharmacodynamic models of in vitro fungistatic and fungicidal effects against Candida albicans

Mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) models describing the fungistatic activity of fluconazole and the fungicidal activity of caspofungin were developed using dynamic in vitro models. Antifungal-drug pharmacokinetics was simulated in vitro, assuming a one-compartment model with an elimination half-life of 3 h and using a wide (1 to 10,000) range of initial concentrations. The number of CFUs over time was determined for up to 31 h and used for PK-PD modeling. A model incorporating first-order natural growth and natural death, plus a maximum number of viable Candida cells, was used to characterize Candida growth in the absence of a drug. Fluconazole was considered to inhibit Candida growth and caspofungin to stimulate Candida death according to an Emax pharmacodynamic model. The data were analyzed with Nonmem, using a population approach. A good fit of the data was obtained with satisfactory estimates of PK-PD parameters, especially with drug concentrations producing 50% of the maximal effect: 50% inhibitory concentrations for fluconazole growth inhibition and 50% effective concentrations for caspofungin death stimulation. In conclusion, mechanistic PK-PD models were successfully developed to describe, respectively, the fungistatic and fungicidal activities of fluconazole and caspofungin in vitro. These models provide much better information on the drug effects over time than the traditional PK-PD index based on MICs. However, they need to be further characterized.

Antifungal susceptibility of bloodstream yeasts isolated at a public children’s hospital in Brazil: comparison of the Etest® and the AFST–EUCAST microdilution method

This study compared the minimum inhibitory concentration (MIC) results from the proposed standard methods of the Antifungal Susceptibility Testing Subcommittee of the European Committee on Antibiotic Susceptibility Testing (AFST–EUCAST) with the commercial system Etest® in the evaluation of susceptibility to flucytosine, fluconazole, itraconazole, voriconazole, and amphotericin B of 136 Candida spp. isolated from the blood of hospitalized children. The results presented a greater agreement among Etest® MICs ±2 log2 dilutions of AFST–EUCAST for fluconazole (98.1% and 96.3%) and voriconazole (100% and 100%) for Candida albicans and Candida parapsilosis . For Candida glabrata , the agreement was greater only for fluconazole (81.8%) and voriconazole (100%). For amphotericin B, the agreement between the methods was low for all species. The agreement percentage among the Etest® and AFST–EUCAST susceptibility profiles was high according to the MIC breakpoints recommended by the M27-A2 protocol for the majority of the yeasts, except for fluconazole and itraconazole against Candida tropicalis and for itraconazole against C. glabrata and Candida krusei . According to both methodologies, a great number of Candida spp. isolates showed an in vitro susceptibility to all evaluated antifungal agents. Overall, both procedures can be reliable techniques for susceptibility tests of yeasts, but the assessment of interlaboratory agreement and correlation of MICs by different methods with in vivo response are of great importance.

Animal models: an important tool in mycology

Animal models of fungal infections are, and will remain, a key tool in the advancement of the medical mycology. Many different types of animal models of fungal infection have been developed, with murine models the most frequently used, for studies of pathogenesis, virulence, immunology, diagnosis, and therapy. The ability to control numerous variables in performing the model allows us to mimic human disease states and quantitatively monitor the course of the disease. However, no single model can answer all questions and different animal species or different routes of infection can show somewhat different results. Thus, the choice of which animal model to use must be made carefully, addressing issues of the type of human disease to mimic, the parameters to follow and collection of the appropriate data to answer those questions being asked. This review addresses a variety of uses for animal models in medical mycology. It focuses on the most clinically important diseases affecting humans and cites various examples of the different types of studies that have been performed. Overall, animal models of fungal infection will continue to be valuable tools in addressing questions concerning fungal infections and contribute to our deeper understanding of how these infections occur, progress and can be controlled and eliminated.

Farmacología de los azoles

Azole antifungals have different pharmacokinetic characteristics: complete oral absorption for Voriconazole, and to a lesser extent for fluconazole. The absorption of posaconazole and itraconazole increases with food intake. All of them have high tissue distribution with low plasma concentrations, especially low in the case of posaconazole and itraconazole. Posaconazole and itraconazole have high plasmatic protein binding and consequently both have a very low free fraction. Elimination of azole antifungals is through a metabolic pathway with CYP450 isoenzymes, and has a non linear pharmacokinetics with a high risk of interation with other drugs since azoles have the ability of CYP450 isoenzymes inhibition. Possibly the parameter that defines more precisely their efficacy is AUIC with an optimum value near 20, although cut-off values must be defined since some azoles may have difficulty to reach this value.

Single-dose pharmacokinetics of intravenous itraconazole and hydroxypropyl-beta-cyclodextrin in infants, children, and adolescents

This investigation was designed to evaluate the single-dose pharmacokinetics of itraconazole, hydroxyitraconazole, and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) after intravenous administration to children at risk for fungal infection. Thirty-three children aged 7 months to 17 years received a single dose of itraconazole (2.5 mg/kg in 0.1-g/kg HP-beta-CD) administered over 1 h by intravenous infusion. Plasma samples for the determination of the analytes of interest were drawn over 120 h and analyzed by high-pressure liquid chromatography, and the pharmacokinetics were determined by traditional noncompartmental analysis. Consistent with the role of CYP3A4 in the biotransformation of itraconazole, a substantial degree of variability was observed in the pharmacokinetics of this drug after IV administration. The maximum plasma concentrations (C(max)) for itraconazole, hydroxyitraconazole, and HP-beta-CD averaged 1,015 +/- 692 ng/ml, 293 +/- 133 ng/ml, and 329 +/- 200 mug/ml, respectively. The total body exposures (area under the concentration-time curve from 0 to 24 h) for itraconazole, hydroxyitraconazole, and HP-beta-CD averaged 4,922 +/- 6,784 ng.h/ml, 3,811 +/- 2,794 ng.h/ml, and 641.5 +/- 265.0 mug.h/ml, respectively, with no significant age dependence observed among the children evaluated. Similarly, there was no relationship between age and total body clearance (702.8 +/- 499.4 ml/h/kg); however, weak associations between age and the itraconazole distribution volume (r(2) = 0.18, P = 0.02), C(max) (r(2) = 0.14, P = 0.045), and terminal elimination rate (r(2) = 0.26, P < 0.01) were noted. Itraconazole infusion appeared to be well tolerated in this population with a single adverse event (stinging at the site of infusion) deemed to be related to study drug administration. Based on the findings of this investigation, it appears that intravenous itraconazole can be administered to infants beyond 6 months, children, and adolescents using a weight-normalized approach to dosing.

Monitoring plasma voriconazole levels may be necessary to avoid subtherapeutic levels in hematopoietic stem cell transplant recipients

BACKGROUND

Low voriconazole levels have been associated with a higher failure rate in patients with confirmed fungal infections.

METHODS

Steady-state plasma trough voriconazole levels were measured after at least 5 days of therapy in 87 patients with hematologic malignancies on 201 separate occasions (1-5 levels per patient; median, 2). Most patients (90%) had undergone allogeneic hematopoietic stem cell transplantation. The daily voriconazole dose, administered in 2 divided doses, was 200 mg (n = 4), 400 mg (n = 151), 500 mg (n = 20), 600 mg (n = 18), and 800 mg (n = 8); corresponding to 2.0-16.3 (median, 5.4) mg/kg. Plasma voriconazole levels were 0-12.5 microg/mL (median, 1.2). Voriconazole was undetectable (<0.2 mug/mL) in 15%.

RESULTS

The correlation between dose and levels was weak (r = 0.14; P = .045). The median absolute daily drug dose (400 mg) was identical in groups of patients with levels of 0, 0.2 to 0.5, >0.5 to 2.0, >2.0 to 5.0, and >5.0. Whereas the daily drug dose in mg/kg was significantly higher when the levels were >5.0 microg/mL, there was no consistent relation between dose and level below that threshold. In adult patients getting standard doses of voriconazole orally, the drug levels are highly variable. Based on limited available data, between a quarter and two-thirds of these levels could potentially be associated with a lower likelihood of response or a higher likelihood of failure.

CONCLUSIONS

Future voriconazole studies should incorporate prospective therapeutic drug monitoring and consideration should be given to checking levels in patients receiving the drug for confirmed, life-threatening fungal infections.

Validation of rapid and simple LC-MS/MS method for determination of voriconazole in rat plasma

A rapid, simple and sensitive LC-MS/MS analytical method was developed and validated for the determination of voriconazole (VRC) in rat plasma, using ketoconazole as internal standard (IS). Analysis was performed on a Shimadzu HPLC system using a Shimadzu C18 column and isocratic elution with acetonitrile-water-formic acid (60:40:0.05, v/v/v), at a flow of 1.0 mL/min (split ratio 1:5), and a mass spectrometer Micromass, equipped with a double quadrupole and an electrospray ionization interface, operated in a positive mode. Plasma samples were deproteinized with methanol (1:2) and 30 microL of the supernatant was injected into the system. The retention times of VRC and IS were approximately 3.3 and 2.7 min, respectively. Calibration curves in spiked plasma were linear over the concentration range of 50-2500 ng/mL with determination coefficient >0.98. The lower limit of quantification was 50 ng/mL. The accuracy of the method was within 5%. Intra- and inter-day relative standard deviations were less or equal to 12.5 and 7.7%, respectively. The applicability of the LC-MS-MS method for pharmacokinetic studies was tested using plasma samples obtained after intravenous administration of VRC to male Wistar rats. The reported method provided the necessary sensitivity, linearity, precision, accuracy, and specificity to allow the determination of VRC in pre-clinical pharmacokinetic studies.

Pharmacokinetics and pharmacodynamics of antifungals

Application of pharmacodynamic principles to antifungal drug therapy of Candida and Aspergillus infections has provided and understanding of the relationship between drug dosing and treatment efficacy. Observations of the pharmacodynamics of triazoles and AmB have correlated with the results of clinical trials and have proven useful for validation of in vitro susceptibility breakpoints. Although there remain many unanswered questions regarding antifungal pharmacodynamics, available data suggest usefulness in the application of pharmacodynamics to antifungal clinical development. Future application of these principles should aid in the design of optimal combination antifungal therapies.

Simultaneous quantification of voriconazole and posaconazole in human plasma by high-performance liquid chromatography with ultra-violet detection

A sensitive and selective high-performance liquid chromatographic (HPLC) method with ultra-violet detection has been developed and validated for the simultaneous determination of posaconazole and voriconazole, two systemic anti-fungal agents. An internal standard diazepam was added to 100 microL of human plasma followed by 3 mL of hexane-methylene chloride (70:30, v/v). The organic layer was evaporated to dryness and the residue was reconstituted with 100 microL of mobile phase before being injected in the chromatographic system. The compounds were separated on a C8 column using sodium potassium phosphate buffer (0.04 M, pH 6.0): acetonitrile:ultrapure water (45:52.5:2.5, v/v/v) as mobile phase. All compounds were detected at a wavelength of 255 nm. The assay was linear and validated over the range 0.2-10.0 mg/L for voriconazole and 0.05-10.0 mg/L for posaconazole. The biases were comprised between -3 and 5% for voriconazole and -2 and 8% for posaconazole. The intra- and inter-day precisions of the method were lower than 8% for the routine quality control (QC). The mean recovery was 98% for voriconazole and 108% for posaconazole. This method provides a useful tool for therapeutic drug monitoring.

Inadequacy of fluconazole dosing in patients with candidemia based on Infectious Diseases Society of America (IDSA) guidelines

INTRODUCTION

Based on Infectious Diseases Society of America (IDSA) guidelines, inappropriate fluconazole therapy in patients with candidemia is defined as an empiric dose <6 mg/kg/d, <12 mg/kg/d after Candida glabrata identification, or continued fluconazole use after identification of Candida krusei. However, the extent to which inappropriate antifungal therapy is due to improper dosing or drug selection has not been well investigated. The objectives of this study were to assess the incidence of inappropriate fluconazole therapy in patients with candidemia and to identify variables associated with inappropriate therapy.

METHODS

Retrospective cohort study from four medical centers of hospitalized patients with candidemia prescribed fluconazole. Appropriateness of fluconazole dosages (adjusted for renal dysfunction) was assessed at the time of symptom onset and after Candida identification.

RESULTS

Patients (206) were identified. Sixty-one of 112 (55%) patients who were given empiric therapy received an initial dose of fluconazole <6 mg/kg. After identification of the Candida species, 97 of 206 (47%) patients received inadequate fluconazole therapy based on IDSA guideline recommendations due to a fluconazole dose <12 mg/kg after isolation of C. glabrata (12%), continued use of fluconazole after isolation of C. krusei (3%), or a dose <6 mg/kg for all other Candida species (32%). Using multivariate logistic regression, increased weight in 1-kg increments (OR: 1.02; p = 0.0142) and a creatinine clearance (CRCL) >50 ml/minute (OR: 3.17; p = 0.0003) were associated with increased risk of inadequate fluconazole therapy.

CONCLUSION

A high prevalence of suboptimal dosing of fluconazole given empirically or after Candida species identification was documented. Increased weight and CRCL were significant predictors of inadequate fluconazole doses.

Comparative analysis of Etest and broth microdilution method (AFST-EUCAST) for trends in antifungal drug susceptibility testing of Brazilian Cryptococcus neoformans isolates

A prospective study was performed to evaluate the correlation between the proposed standard of the Antifungal Susceptibility Testing Subcommittee of the European Committee on Antibiotic Susceptibility Testing (AFST-EUCAST) (document 7.1) and the commercial system Etest for determining the MICs of flucytosine, amphotericin B, fluconazole, itraconazole and voriconazole for a collection of 100 clinical and environmental isolates of Cryptococcus neoformans. The agreements among Etest MICs within +/-2 log2 dilutions of AFST-EUCAST standard MICs were greater for flucytosine, fluconazole and voriconazole (76, 78 and 88 %, respectively) than for amphotericin B (5 %), the lowest agreement, and itraconazole (67 %). Overall, the correlation coefficients were statistically significant (P<0.05), and it is suggested that the Etest and AFST-EUCAST method are reliable alternatives and present good correlation for all drugs evaluated except amphotericin B. However, the observed differences related to MICs for susceptible, susceptible dose dependent and resistant strains between the methods suggest that it will be necessary to carry out further studies, including assessment of interlaboratory agreement and correlation of MICs by different methods with in vivo response.

Pharmacokinetic/pharmacodynamic profile of voriconazole

Voriconazole is the first available second-generation triazole with potent activity against a broad spectrum of clinically significant fungal pathogens, including Aspergillus,Candida, Cryptococcus neoformans, and some less common moulds. Voriconazole is rapidly absorbed within 2 hours after oral administration and the oral bioavailability is over 90%, thus allowing switching between oral and intravenous formulations when clinically appropriate. Voriconazole shows nonlinear pharmacokinetics due to its capacity-limited elimination, and its pharmacokinetics are therefore dependent upon the administered dose. With increasing dose, voriconazole shows a superproportional increase in area under the plasma concentration-time curve (AUC). In doses used in children (age < 12 years) voriconazole pharmacokinetics appear to be linear. Steady-state plasma concentrations are reached approximately 5 days after both intravenous and oral administration; however, steady state is reached within 24 hours with voriconazole administered as an intravenous loading dose. The volume of distribution of voriconazole is 2-4.6 L/kg, suggesting extensive distribution into extracellular and intracellular compartments. Voriconazole was measured in tissue samples of brain, liver, kidney, heart, lung as well as cerebrospinal fluid. The plasma protein binding is about 60% and independent of dose or plasma concentrations. Clearance is hepatic via N-oxidation by the hepatic cytochrome P450 (CYP) isoenzymes, CYP2C19, CYP2C9 and CYP3A4. The elimination half-life of voriconazole is approximately 6 hours, and approximately 80% of the total dose is recovered in the urine, almost completely as metabolites. As with other azole drugs, the potential for drug interactions is considerable. Voriconazole shows time-dependent fungistatic activity against Candida species and time-dependent slow fungicidal activity against Aspergillus species. A short post-antifungal effect of voriconazole is evident only for Aspergillus species. The predictive pharmacokinetic/pharmacodynamic parameter for voriconazole treatment efficacy in Candida infections is the free drug AUC from 0 to 24 hour : minimum inhibitory concentration ratio.

Association of fluconazole area under the concentration-time curve/MIC and dose/MIC ratios with mortality in nonneutropenic patients with candidemia

The present study tested in vitro susceptibility of Candida bloodstream isolates to fluconazole to determine if the ratio of the fluconazole area under the concentration-time curve (AUC) or weight-normalized daily dose (dose(wn)) to MIC correlated with mortality. Fluconazole susceptibility and outcome data were determined for 77 patients with a positive Candida blood culture between 2002 and 2005. The most commonly isolated Candida species were C. albicans (64%), C. glabrata (14%), C. parapsilosis (8%), C. tropicalis (6%), and C. lusitaniae (4%). Only two isolates were classified as fluconazole resistant by the CLSI M27-A2 method. Fluconazole MICs were highest against C. glabrata relative to other Candida species. Overall the crude mortality assessed at hospital discharge was 19.4% (n = 15). Mortality rates by species were as follows: C. albicans, 16.3%; C. glabrata, 36.4%; C. parapsilosis, 0%; C. tropicalis, 0%; C. lusitaniae, 33.3%. A mortality rate of 50% was noted among patients infected with nonsusceptible isolates (MIC > or = 16 microg/ml) compared to 18% for patients infected with susceptible (MIC < or = 8 microg/ml) isolates (P = 0.17). The fluconazole dose(wn)/MIC (24-h) values were significantly higher for the 62 survivors (13.3 +/- 10.5 [mean +/- standard deviation]) compared to the 15 nonsurvivors (7.0 +/- 8.0) (P = 0.03). The fluconazole AUC/MIC (24 h) values also trended higher for survivors (775 +/- 739) compared to nonsurvivors (589 +/- 715) (P = 0.09). These data support the dose-dependent properties of fluconazole. Underdosing fluconazole against less-susceptible Candida isolates has the potential to increase the risk of mortality associated with candidemia.