Pharmacokinetic and Exposure Response Analysis of the Double-Blind Randomized Study of Posaconazole and Voriconazole for Treatment of Invasive Aspergillosis

BACKGROUND AND OBJECTIVE

A double-blind phase 3 study was conducted to compare posaconazole 300 mg intravenously (IV)/300 mg orally once daily (twice daily day 1) with voriconazole 4 mg/kg IV twice daily/200 mg orally twice daily (6 mg/kg day 1) for treatment of invasive aspergillosis. This analysis was conducted to summarize the pharmacokinetics and exposure-response relationships of posaconazole and voriconazole using plasma trough concentration (Ctrough) as a surrogate for exposure from the double-blind phase 3 study.

METHODS

The pharmacokinetic evaluable population included all intention-to-treat (ITT) participants with at least one plasma concentration during the treatment period. Treatment blinding was maintained without therapeutic drug monitoring. Ctrough sampling occurred throughout treatment; efficacy and safety were evaluated using quartiles determined by mean Ctrough concentrations. Exposure efficacy variables included day 42 all-cause mortality (primary study endpoint) and global clinical response. Exposure safety variables included all adverse events and treatment-related adverse events.

RESULTS

The pharmacokinetic analysis population included 506 of 575 ITT participants (437 with Ctrough concentrations: 228 posaconazole, 209 voriconazole). No trend was seen across quartiles of posaconazole Ctrough for the key efficacy endpoint of all-cause mortality through day 42. Participants in the highest quartile of voriconazole Ctrough had higher all-cause mortality through day 42 than participants in the lower three quartiles of voriconazole Ctrough. Similar findings were observed for global clinical response and Ctrough. No clear exposure safety trend by quartile was seen for posaconazole or voriconazole.

CONCLUSIONS

A strong exposure-response relationship was not observed across the range of exposure from the administered doses and formulations for posaconazole or voriconazole.

TRIAL REGISTRATION

NCT01782131; registered January 30, 2013.

Model-Informed Dose Justifications of Posaconazole in Japanese Patients for Prophylaxis and Treatment Against Fungal Infection

Posaconazole is a globally approved broad-spectrum triazole antifungal compound. In Japanese patients, posaconazole has identical dosing regimens as those approved globally for both tablet and intravenous formulations. This article aims to describe a model-informed approach for dose justification of posaconazole in the Japanese population as either high-risk patients with fungal infections (prophylaxis patients) or patients with fungal infections (treatment patients). A simultaneous population pharmacokinetic (PK) model for tablet and intravenous formulation was developed on the basis of a data set including Japanese data from healthy participants and treatment patients. The PK profiles and exposure distributions in Japanese patients were predicted and compared against foreign patients, that is, patients outside of Japan. Relationships between the post hoc posaconazole exposures and frequently observed clinical adverse events were evaluated. Although clinical trials for Japanese prophylaxis patients were not conducted, PK profiles in Japanese prophylaxis patients were predicted using the population PK model and demographic covariate information obtained from the published literature. Based upon the globally approved dosing regimen, posaconazole exposure distribution was predicted to be the highest in Japanese treatment patients, and generally similar between Japanese and foreign prophylaxis patients. Exposures in Japanese patients exceeded the efficacy target level (500 ng/mL). Safety profiles in Japanese treatment patients with the highest exposures were clinically acceptable without specific concerns to Japanese patients and appeared to have no relationship with posaconazole exposures. From PK, safety, and efficacy perspectives, the use of the same dosing regimen as in foreign patients was justified in Japanese prophylaxis and treatment patients.

Phase 1b/3 Pharmacokinetics and Safety Study of Intravenous Posaconazole in Adult Asian Participants at High Risk for Invasive Fungal Infections

Introduction

Antifungal prophylaxis in patients at high risk for invasive fungal infections (IFIs), such as those with acute myeloid leukemia or myelodysplastic syndromes, continues to be underused in Asia, despite the fact that it reduces IFI-related death and increases IFI-free survival. We characterized the pharmacokinetics (PK) and safety of the intravenous (IV) formulation of posaconazole in adult Asian participants at high risk for IFI.

Methods

Participants received posaconazole IV 300 mg twice on day 1, posaconazole IV 300 mg once daily on days 2–10, and posaconazole IV 300 mg once daily or oral suspension 200 mg 3 times daily for up to 18 days for a maximum of 28 days. There were two PK sampling groups: intensive and sparse. Sparse trough PK sampling was collected from all participants on days 3, 6, 10, 15, 22, and 28/end of treatment. The intensive PK group had additional sampling performed over 24 h on day 10. Primary end points were steady state average concentration (C_avg,ss) and percentage of participants with C_avg,ss ≥ 500 ng/mL. Safety was assessed up to day 30/end of treatment.

Results

Seventy participants with acute myelogenous leukemia were enrolled, 30 in the intensive PK group and 40 in the sparse PK group; 57 participants completed the study, 26 in the intensive PK group and 31 in the sparse PK group. On day 10, arithmetic mean C_avg,ss was 2986 ng/mL [coefficient of variation (%CV), 36%; range, 1409–5930 ng/mL]; 100% of participants in the intensive PK group (n/N = 27/27) had C_avg,ss ≥ 500 ng/mL. Arithmetic mean (%CV) C_min was 2474 (50.4%) and 2466 ng/mL (42.4%) in the intensive and sparse PK groups on day 10, respectively. Safety was similar to that of previous posaconazole formulations.

Conclusion

In Asian participants at high risk for IFIs, IV posaconazole achieved the target exposure associated with efficacy that was previously established for supporting global registration of posaconazole for IV administration and was generally well tolerated.

Clinical trial registration

ClinicalTrials.gov, NCT03336502.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12325-021-02012-1.

Pharmacokinetics and safety of posaconazole intravenous solution and powder for oral suspension in children with neutropenia: an open-label, sequential dose-escalation trial

Posaconazole is approved for use in adults as an intravenous (IV) solution and two different oral formulations (a suspension and an improved bioavailability tablet). Data on the pharmacokinetics (PK), dosing and safety of posaconazole in children are limited. A novel powder for oral suspension (PFS) offers the bioavailability of the tablet formulated for weight-based dosing in children. A non-randomised, open-label, sequential dose-escalation, phase 1b trial evaluated the PK and safety of posaconazole IV and PFS in children aged 2 to 17 years with documented or expected neutropenia (ClinicalTrials.gov, NCT02452034; MSD protocol number, MK-5592-P097). Participants received posaconazole IV 3.5, 4.5 or 6.0 mg/kg/d for ≥10 days, with an option to switch to posaconazole PFS at the identical dose for ≤18 days. The target exposure was a mean within-dose cohort average steady-state plasma concentration (C_avg) of ~1200 ng/mL, with ~90% of participants achieving C_avg between 500 and 2500 ng/mL. Doses of 4.5 and 6.0 mg/kg/d achieved the PK target of ~90% of participants with a C_avg ≥500 ng/mL. PFS resulted in lower posaconazole exposures than IV across age groups at all doses. Posaconazole IV and PFS were well tolerated and had safety profiles similar to those reported for adults. Posaconazole PK following IV and PFS administration was well characterised by the data and enable selection of appropriate paediatric doses. Both formulations were well tolerated without dose-, exposure- or age-related differences in the safety profiles.

Pharmacokinetics and Safety of Posaconazole Tablet Formulation in Chinese Participants at High Risk for Invasive Fungal Infection

INTRODUCTION

This study characterized the multidose pharmacokinetic (PK) characteristics of posaconazole tablets used as prophylactic antifungal therapy in Chinese patients with acute myelogenous leukemia (AML) at risk for invasive fungal infection (IFI).

METHODS

Participants in this open-label, single-arm, phase 1b study received posaconazole 300 mg twice daily on day 1 and then once daily for up to 28 days. In the intensive PK sampling subgroup, posaconazole was administered under fasting conditions on days 1 and 8, and blood samples were regularly collected over 24 h. Trough PK sampling was conducted in all participants on days 1, 2, 3, 8, 14, 21, and 28 without regard for food intake. Population PK characteristics were predicted using PK modeling. Primary endpoints were steady-state average concentration (C_avg) and percentage of participants with steady-state C_avg (predicted and observed) > 500 ng/ml. Treatment safety and efficacy were secondary endpoints.

RESULTS

Sixty-five adult Chinese participants were enrolled. On day 8, steady-state arithmetic mean C_avg was 1610 ng/ml (% coefficient of variation [%CV] 42.8%) in the intensive PK subgroup (n = 20). All participants achieved a steady-state C_avg > 500 ng/ml. Predicted C_avg (pC_avg) was 1770 ng/ml (%CV 33.7%) in the total population (n = 64); 92.2% of participants had pC_avg values ≥ 500 ng/ml (n = 59). The posaconazole tablet safety profile was consistent with that of the oral formulation, and the IFI rate was 3%.

CONCLUSION

In Chinese AML patients, the posaconazole 300-mg tablet provided PK data comparable with those of previous studies and was generally well tolerated and efficacious.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, NCT02387983.

1558. A Population Pharmacokinetic Model for Posaconazole Intravenous Solution and Oral Powder for Suspension Formulations in Pediatric Patients With Neutropenia

Background

Posaconazole is approved in adults for prophylaxis and treatment of invasive fungal disease. Two formulations that offer weight-based dosing—intravenous (IV) and oral powder for suspension (PFS)—are being evaluated in children. A population pharmacokinetic (popPK) approach was used to characterize and predict the PK exposure of posaconazole PFS and IV formulations in children to identify dosages associated with achieving a target PK of 1200 ng/mL as the mean Cavg and individual Cavg ≥500 ng/mL and <2500 ng/mL in ~90% of patients.

Methods

A popPK model was developed through nonlinear mixed-effects modeling using data obtained from a trial in children with neutropenia (ClinicalTrials.gov, NCT02452034; Merck protocol, MK-5592-097). Three dose cohorts (3.5, 4.5, and 6 mg/kg/day [≤300 mg/day]) were studied in two age groups (2–<7 years and 7–17 years). Posaconazole IV was administered twice on day 1 then once daily through at least day 10, followed by PFS once daily through day 28 at clinician discretion. A compartmental model, including both formulations, was fit to the data. Model selection was based on the Log-Likelihood Criterion, goodness-of-fit plots, and scientific plausibility. Significance of the covariates was assessed in a stepwise forward inclusion/backward procedure. An additional assessment characterized the impact of different food covariates on bioavailability.

Results

An open one-compartmental PK model with first-order absorption and estimated bioavailability, as well as allometrically scaled effects of body weight on clearance and volume, adequately described the PK of posaconazole IV and PFS formulations. Model predictions are shown in the Table. Effects of the different food covariates were not statistically significant. Simulations indicated that for the 6-mg/kg/d dose, model-predicted Cavg generally met PK targets. Model-predicted Cavg was ≥500 ng/mL in >90% of subjects in all cohorts. The 1200-ng/mL target geometric mean Cavg was achieved for all but the 2–<7 years cohort receiving the PFS formulation.

Conclusion

This popPK-based analysis demonstrated that the 6-mg/kg/d dose of IV or PFS posaconazole formulation (≤300 mg/days) is appropriate for children (2–17 years) and that PFS can be administered without regard to food.

Disclosures

All authors: No reported disclosures.

Safety, Tolerability, and Pharmacokinetics (PK) of Posaconazole (POS) Intravenous (IV) Solution and Oral Powder for Suspension in Children With Neutropenia

Background

POS, a triazole antifungal approved for prophylaxis and treatment of adults with invasive fungal infections, is available as an IV solution and 2 oral formulations: an oral suspension and a tablet with improved bioavailability. A novel powder for oral suspension (PFS) has been developed to offer the bioavailability of the tablet in a formulation optimized for weight-based dosing in children. The objective of this study is to evaluate the safety, tolerability, and PK of POS IV and POS PFS in pediatric patients (patients) aged 2 to 17 y with documented or expected neutropenia.

Methods

This is an ongoing, nonrandomized, multicenter, open-label, sequential dose-escalation study evaluating POS IV and POS PFS. Pts are divided into 2 age groups: 2 to <7 and 7 to 17 y. Each age group includes 2 dose cohorts: 3.5 mg/kg/d and 4.5 mg/kg/d. Patients received 10–28 d of POS initially as IV solution with the option to switch to PFS after 10 d for the remainder of the treatment period. PK sampling was conducted after 7–10 days on each formulation. Target PK exposure was ~90% of patients with C_avg 500–2,500 ng/mL. C_avg is defined as AUC over a dosing interval.

Results

57 of 66 patients (86%) who received POS IV were PK evaluable; 35 patients (53%) received POS PFS, of whom 30 (86%) were PK evaluable. Table 1 shows C_avg and proportion in target range of PK-evaluable patients by dose cohort and age group. The safety profiles of POS IV and PFS were similar to those previously reported for adults treated with oral/IV POS.

Conclusion

POS PFS resulted in lower POS exposure than IV across age groups at both dose levels. POS exposure was substantially lower in the younger age group for both IV and PFS. At 4.5 mg/kg, the patients in this study achieved the predefined target but did not achieve systemic exposures (mean C_avg) comparable to those seen in adults with POS IV or tablet. These results suggest that study of POS IV and PFS dosing >4.5 mg/kg/d is warranted.

Disclosures

A. H. Groll, Merck Sharp & Dohme: Consultant, Investigator, Scientific Advisor and Speaker’s Bureau, Consulting fee and Speaker honorarium. T. Lehrnbecher, Merck/MSD: Scientific Advisor and Speaker’s Bureau, Speaker honorarium. Astellas: Scientific Advisor and Speaker’s Bureau, Speaker honorarium. Basilea: Scientific Advisor, Consulting fee. Gilead: Investigator, Scientific Advisor and Speaker’s Bureau, Research grant and Speaker honorarium.Pfizer: Speaker’s Bureau, Speaker honorarium. W. Steinbach, Merck: Consultant, Consulting fee. Astellas: Consultant, Consulting fee. Gilead: Consultant, Consulting fee. R. Murray, Merck: Employee, Salary. A. Paschke, Merck: Employee, Salary. E. Mangin, Merck: Employee, Salary. G. A. Winchell, Merck: Research Contractor, Consulting fee. C. J. Bruno, Merck: Employee and Shareholder, Salary and Stock.

Model-based decision making in early clinical development: minimizing the impact of a blood pressure adverse event

We describe how modeling and simulation guided program decisions following a randomized placebo-controlled single-rising oral dose first-in-man trial of compound A where an undesired transient blood pressure (BP) elevation occurred in fasted healthy young adult males. We proposed a lumped-parameter pharmacokinetic-pharmacodynamic (PK/PD) model that captured important aspects of the BP homeostasis mechanism. Four conceptual units characterized the feedback PD model: a sinusoidal BP set point, an effect compartment, a linear effect model, and a system response. To explore approaches for minimizing the BP increase, we coupled the PD model to a modified PK model to guide oral controlled-release (CR) development. The proposed PK/PD model captured the central tendency of the observed data. The simulated BP response obtained with theoretical release rate profiles suggested some amelioration of the peak BP response with CR. This triggered subsequent CR formulation development; we used actual dissolution data from these candidate CR formulations in the PK/PD model to confirm a potential benefit in the peak BP response. Though this paradigm has yet to be tested in the clinic, our model-based approach provided a common rational framework to more fully utilize the limited available information for advancing the program.

Potential for interactions between caspofungin and nelfinavir or rifampin

The potential for interactions between caspofungin and nelfinavir or rifampin was evaluated in two parallel-panel studies. In study A, healthy subjects received a 14-day course of caspofungin alone (50 mg administered intravenously [IV] once daily) (n = 10) or with nelfinavir (1,250 mg administered orally twice daily) (n = 9) or rifampin (600 mg administered orally once daily) (n = 10). In study B, 14 subjects received a 28-day course of rifampin (600 mg administered orally once daily), with caspofungin (50 mg administered IV once daily) coadministered on the last 14 days, and 12 subjects received a 14-day course of caspofungin alone (50 mg administered IV once daily). The coadministration/administration alone geometric mean ratio for the caspofungin area under the time-concentration profile calculated for the 24-h period following dosing [AUC(0-24)] was as follows (values in parentheses are 90% confidence intervals [CIs]): 1.08 (0.93-1.26) for nelfinavir, 1.12 (0.97-1.30) for rifampin (study A), and 1.01 (0.91-1.11) for rifampin (study B). The shape of the caspofungin plasma profile was altered by rifampin, resulting in a 14 to 31% reduction in the trough concentration at 24 h after dosing (C(24h)), consistent with a net induction effect at steady state. Both the AUC and the C(24h) were elevated in the initial days of rifampin coadministration in study A (61 and 170% elevations, respectively, on day 1) but not in study B, consistent with transient net inhibition prior to full induction. The coadministration/administration alone geometric mean ratio for the rifampin AUC(0-24) on day 14 was 1.07 (90% CI, 0.83-1.38). Nelfinavir does not meaningfully alter caspofungin pharmacokinetics. Rifampin both inhibits and induces caspofungin disposition, resulting in a reduced C(24h) at steady state. An increase in the caspofungin dose to 70 mg, administered daily, should be considered when the drug is coadministered with rifampin.

Pharmacokinetics of indinavir and ritonavir administered at 667 and 100 milligrams, respectively, every 12 hours compared with indinavir administered at 800 milligrams every 8 hours in human immunodeficiency virus-infected patients

Human immunodeficiency virus (HIV) patients on nucleoside or nucleotide reverse transcriptase inhibitors with HIV RNA at <1,000 copies/ml were randomized in an open-label study to administration of combined indinavir/ritonavir (IDV/RTV) at 667/100 mg every 12 h (q12h) or IDV alone at 800 mg q8h to determine the regimens' pharmacokinetics. On day 14, plasma IDV and RTV levels were determined over 24 h. Noncompartmental pharmacokinetics (minimum concentration of drug in serum [C(min)], area under the concentration-time curve from 0 to 24 h [AUC(0-24)], and maximum concentration of drug in serum [C(max)]) were expressed as geometric mean values with 90% confidence intervals (CI). The primary hypothesis was that the lower bound of the protocol-specified 90% CI for the geometric mean C(min) ratio of the combination compared to IDV alone regimen would be >/=2. Twenty-seven patients were enrolled, and 24 (15 male; average age, 42 years) completed the study. The C(min), AUC(0-24), and C(max) for IDV/RTV compared to IDV alone were 1,511 versus 250 nM, 119,557 versus 77,034 nM . h, and 10,428 versus 10,407 nM, respectively. Corresponding relationships for IDV/RTV compared to IDV alone were a 6.0-fold increase in C(min) (90% CI, 4.0, 9.3), an increase in AUC(0-24) (1.5-fold, 90% CI, 1.2, 2.0), and no increase in C(max). Adverse events were similar and generally mild, with no cases of nephrolithiasis. The geometric mean ratio of IDV C(min) for IDV/RTV compared to IDV was at least 2 by a lower bound of the 90% CI, satisfying the primary hypothesis. The C(max) was not increased, suggesting an IDV/RTV 667/100-mg toxicity profile may be similar to that of unboosted IDV.

Indinavir and rifabutin drug interactions in healthy volunteers

Two studies examined the pharmacokinetics of indinavir and rifabutin when coadministered in healthy subjects. Rifabutin, which induces the expression of cytochrome P450 (CYP) 3A, and indinavir, which inhibits that enzyme system, are frequently coadministered in patients infected with HIV. The second study was undertaken to determine if altering the dose of rifabutin coadministered with indinavir would minimize the drug interaction observed in the first study. Two studies, each with a three-period crossover design, were performed. In study 1, standard doses of rifabutin and indinavir (300 mg of rifabutin qd and 800 mg indinavir q8h) were administered as monotherapy (with placebo to the other drug) or in combination to 10 volunteers for 10 days. In study 2, 150 mg qd of rifabutin together with 800 mg q8h of indinavir, 300 mg qd of rifabutin alone, or 800 mg q8h of indinavir alone was administered to 14 volunteers for 10 days. In study 1, the geometric mean ratio (GMR) (90% confidence interval [CI]) of the AUC((0-8h)) of indinavir, coadministered with rifabutin 300 mg qd compared to indinavir alone (with rifabutin placebo), was 0.66 (0.56, 0.77), while that of the AUC((0-24h)) of rifabutin, coadministered with indinavir compared to rifabutin alone (with indinavir placebo), was 2.73 (1.99, 3.77). In study 2, the GMR (90% CI) of the AUC((0-8h)) of indinavir, coadministered with rifabutin 150 mg qd compared to indinavir alone, was 0.68 (0.60, 0.76), while that of the AUC((0-24h)) of rifabutin, when rifabutin 150 mg qd was coadministered with indinavir compared to rifabutin 300 mg qd alone, was 1.54 (1.33, 1.79). For both studies 1 and 2, indinavir and rifabutin administered alone or in combination were generally well tolerated. No clinical or laboratory adverse experience was serious. These data demonstrate the important pharmacokinetic interactions between indinavir and rifabutin when they are coadministered. Indeed, these observations formed the basis for the subsequent ACTG 365 study that explored dose adjustments for these agents in combination regimens to preserve the sustained antiviral activity of indinavir in the absence of adverse events as a result of elevated circulating levels of rifabutin.

Pharmacokinetics of indinavir combined with low-dose ritonavir in human immunodeficiency virus type 1-infected children

So far, no pediatric doses for indinavir combined with ritonavir have been defined. This study evaluated the pharmacokinetics of 400 mg of indinavir/m(2) combined with 125 mg of ritonavir/m(2) every 12 h (q12h) in 14 human immunodeficiency virus type 1-infected children. The area under the concentration-time curve from 0 to 24 h and the minimum concentration of drug in serum for indinavir were similar to those for 800 mg of indinavir-100 mg of ritonavir q12h in adults, while the maximum concentration of drug in serum was slightly decreased, with geometric mean ratios (90% confidence intervals in parentheses) of 1.1 (0.87 to 1.3), 0.96 (0.60 to 1.5), and 0.80 (0.68 to 0.94), respectively.

Disposition of caspofungin: role of distribution in determining pharmacokinetics in plasma

The disposition of caspofungin, a parenteral antifungal drug, was investigated. Following a single, 1-h, intravenous infusion of 70 mg (200 microCi) of [(3)H]caspofungin to healthy men, plasma, urine, and feces were collected over 27 days in study A (n = 6) and plasma was collected over 26 weeks in study B (n = 7). Supportive data were obtained from a single-dose [(3)H]caspofungin tissue distribution study in rats (n = 3 animals/time point). Over 27 days in humans, 75.4% of radioactivity was recovered in urine (40.7%) and feces (34.4%). A long terminal phase (t(1/2) = 14.6 days) characterized much of the plasma drug profile of radioactivity, which remained quantifiable to 22.3 weeks. Mass balance calculations indicated that radioactivity in tissues peaked at 1.5 to 2 days at approximately 92% of the dose, and the rate of radioactivity excretion peaked at 6 to 7 days. Metabolism and excretion of caspofungin were very slow processes, and very little excretion or biotransformation occurred in the first 24 to 30 h postdose. Most of the area under the concentration-time curve of caspofungin was accounted for during this period, consistent with distribution-controlled clearance. The apparent distribution volume during this period indicated that this distribution process is uptake into tissue cells. Radioactivity was widely distributed in rats, with the highest concentrations in liver, kidney, lung, and spleen. Liver exhibited an extended uptake phase, peaking at 24 h with 35% of total dose in liver. The plasma profile of caspofungin is determined primarily by the rate of distribution of caspofungin from plasma into tissues.

Single- and multiple-dose pharmacokinetics of caspofungin in healthy men

Caspofungin, a glucan synthesis inhibitor, is being developed as a parenteral antifungal agent. The pharmacokinetics of caspofungin following 1-h intravenous infusions in healthy men was investigated in four phase I studies. In an alternating two-panel (six men each), rising-single-dose study, plasma drug concentrations increased proportionally with the dose following infusions of 5 to 100 mg. The beta-phase half-life was 9 to 10 h. The plasma drug clearance rate averaged 10 to 12 ml/min. Renal clearance of unchanged drug was a minor pathway of elimination (approximately 2% of the dose). Multiple-dose pharmacokinetics were investigated in a 2-week, serial-panel (5 or 6 men per panel) study of doses of 15, 35, and 70 mg administered daily; a 3-week, single-panel (10 men) study of a dose of 70 mg administered daily; and a parallel panel study (8 men) of a dose of 50 mg administered daily with or without a 70-mg loading dose on day 1. Moderate accumulation was observed with daily dosing. The degree of drug accumulation and the time to steady state were somewhat dose dependent. Accumulation averaged 24% at 15 mg daily and approximately 50% at 50 and 70 mg daily. Mean plasma drug concentrations were maintained above 1.0 microg/ml, a target selected to exceed the MIC at which 90% of the isolates of the most clinically relevant species of Candida were inhibited, throughout therapy with daily treatments of 70 or 50 mg plus the loading dose, while they fell below the target for the first 2 days of a daily treatment of 50 mg without the loading dose. Caspofungin infused intravenously as a single dose or as multiple doses was generally well tolerated. In conclusion, the pharmacokinetics of caspofungin supports the clinical evaluation of once-daily dosing regimens for efficacy against fungal infections.

Cyclobenzaprine pharmacokinetics, including the effects of age, gender, and hepatic insufficiency

The pharmacokinetics and bioavailability of cyclobenzaprine, a widely used muscle relaxant, were investigated in four clinical studies, and the effects of age, gender, and hepatic insufficiency were characterized. Cyclobenzaprine plasma clearance was 689 ml/min, and the bioavailability of a 5 mg oral dose was 0.55. Following oral doses of 2.5 to 10 mg tid in healthy young subjects, cyclobenzaprine pharmacokinetics were linear, and plasma concentrations generally increased proportional to dose. There was about a fourfold accumulation of the drug in plasma on multiple dosing, corresponding to an effective half-life of 18 hours. Steady-state plasma concentrations of cyclobenzaprine in elderly subjects were twice as high as in young subjects following oral doses of 5 mg tid. Steady-state plasma concentration also appeared to be up to twofold higher in subjects with mild hepatic insufficiency compared to healthy controls. The magnitude of any difference in steady-state plasma concentration between males and females appears to be small relative to intersubject variability. A reduction in dose or dosing frequency should be considered in the elderly and in patients with liver disease.

Pharmacokinetic profile and tolerability of indinavir-ritonavir combinations in healthy volunteers

This was a randomized, double-blind, placebo-controlled parallel study in human immunodeficiency virus type 1 (HIV-1)-uninfected healthy subjects to investigate the pharmacokinetic interaction between indinavir (IDV) and ritonavir (RTV). Subjects were allocated to treatment groups of IDV given with RTV in the following milligram doses twice daily: 800 mg of IDV-100 mg of RTV (800-100 mg), 800-200, 800-400, and 400-400 mg, placebo of IDV with RTV doses of 100, 200, and 400 mg, and placebo of both IDV and RTV. Doses of both drugs were administered for 14 days with a low-fat meal and one dose on day 15 with a high-fat meal. Blood was obtained for drug concentration measurements on days 14 and 15. Seventy-three volunteers enrolled in the study: 29 men and 44 women. Fifty-three volunteers completed the study. When compared to standard historical data for 800 mg of IDV every 8 h (q8h), the IDV area under the concentration-time curve for 24 h (AUC(24)) of IDV-RTV regimens 400-400, 800-100, and 800-200 mg were at least 1.4, 2.3, and 3.3 times higher, respectively, regardless of meal. The concentrations at the end of the dosing interval were 10 to 25 times higher than that observed in the standard regimen of 800 mg of IDV q8h for IDV-RTV 800-100 and 800-200 mg regimens, respectively. RTV at 200 mg maximally enhanced the IDV profile. Improved tolerability was associated with IDV-RTV 800-100 mg versus IDV-RTV 800-200, 800-400, and 400-400 mg q12h. The advantages of IDV-RTV twice daily over 800 mg of IDV q8h include no food restrictions and twice-daily dosing. Also, the regimens achieve levels of IDV that may be helpful in suppressing strains of HIV-1 that have reduced susceptibility to IDV or other protease inhibitors.

An extended point-area deconvolution approach for assessing drug input rates

PURPOSE

To describe an extended point-area deconvolution approach for evaluating drug input rates based on the application of piecewise cubic polynomial functions.

METHODS

Both the nonimpulse response data and the impulse reference data were independently represented by the piecewise cubic polynomials to obtain interpolations, numerical integration, and reduced step size for the staircase input rates. A moving average algorithm was employed to compute the input rate estimates. The method was illustrated using data from preclinical and human studies. Simulations were used to examine the effects of data noise.

RESULTS

In all cases examined, the piecewise cubic interpolation functions combined with the moving average algorithm yielded estimates that were reasonable and acceptable. Compared to the standard point-area approach based on the trapezoidal rule, the present method resulted in estimates that were closer to the expected values.

CONCLUSIONS

The point-area deconvolution analysis is one of the preferred approaches in assessing pharmacokinetic and biopharmaceutic data when it is undesirable to assume the functional forms of the input processes. The present method provides improved performance and greater flexibility of this approach.

Use of in vitro drug metabolism data to evaluate metabolic drug-drug interactions in man: the need for quantitative databases

It has become widely accepted that metabolic drug-drug interactions can be forecast using in vitro cytochrome P450 (CYP) data. For any CYP form-inhibitor pair, the magnitude of the interaction will depend on the potency of the inhibitor (inhibition constant, Ki) the concentration of the inhibitor available for inhibition ([I]), the fraction of the substrate dose metabolized by CYP (fm), and the fraction of the CYP-dependent metabolism catalyzed by the inhibited CYP form (e.g., fm,CYP3A4). While progress is being made toward our understanding of the factors necessary for predictions of [I]/Ki in vivo, it is evident that there is a need for quantitative databases that contain in vitro (e.g., Ki, fm,CYP3A4) and in vivo pharmacokinetic/absorption-distribution-metabolism-excretion (PK/ADME) data (e.g., fm) for a large number of marketed drugs. Ultimately, such databases would allow one to integrate all of the data necessary for the prediction of drug-drug interactions and permit the rational evaluation of new drug entities.

The steady-state disposition of indinavir is not altered by the concomitant administration of clarithromycin

STUDY OBJECTIVES

To evaluate the safety and potential pharmacokinetic interaction between indinavir and clarithromycin.

STUDY METHODS

In a randomized, three-period, crossover fashion, 12 healthy adults received the following for 1 week: 800 mg oral indinavir sulfate every 8 hours with placebo, 500 mg oral clarithromycin every 12 hours with placebo, and indinavir sulfate with clarithromycin. Plasma indinavir, clarithromycin, and 14-hydroxyclarithromycin concentrations were determined after the last dose in each treatment period.

RESULTS

Administration of indinavir sulfate with clarithromycin caused a statistically significant increase in four pharmacokinetic parameters: a 58% increase in plasma indinavir concentrations at 8 hours (P = .029), a 47% increase in values for clarithromycin area under the plasma concentration versus time curve from time zero to the last measured concentration [AUC(0-12h); P = .0002], and 49% and 48% decreases in 14-hydroxyclarithromycin AUC(0-12h) and maximum plasma concentration (Cmax) values, respectively (P = .0001 and P = .0001). These effects are not considered to be clinically significant in view of the insignificant effects on the values for indinavir area under the plasma concentration versus time curve from time zero to the last measured concentration [AUC(0-8h)] and Cmax, as well as the safety profile of clarithromycin.

CONCLUSIONS

The combination of indinavir sulfate and clarithromycin is generally well tolerated and can be coadministered without dose adjustment.

Effect of MK-386, a novel inhibitor of type 1 5 alpha-reductase, alone and in combination with finasteride, on serum dihydrotestosterone concentrations in men

Two isozymes (types 1 and 2) of 5 alpha-reductase (5 alpha R; EC 1.3.99.5), with differential tissue distribution, have been identified in humans. These enzymes catalyze the reduction of testosterone (T) to dihydrotestosterone (DHT). The contributions of each of these isozymes to serum and tissue concentrations of DHT remain to be fully defined. Finasteride, a selective inhibitor of type 2 5 alpha R, lowers circulating DHT levels by approximately 70% in men after treatment with 5 mg daily. MK-386 (4,7 beta-dimethyl-4-aza-5 alpha-cholestan-3-one) is a new selective inhibitor of type 1 5 alpha R. A single rising dose, alternating panel, trial in 16 healthy males (age range, 21-25 yr) studied the effect of 0.1-100 mg MK-386. DHT was maximally reduced by 20-30% relative to placebo at MK-386 doses of 10 mg or more, orally, by 24 h posttreatment (P < 0.01 vs. placebo). No consistent effect on T concentrations was evident. In a second trial, finasteride (5 mg) was given for 19 days to 10 healthy young men (age range, 24-47 yr); a 25-mg dose of MK-386 was added for 2 days of combination therapy after at least 10 days of finasteride treatment. Withdrawal of MK-386 was followed by 5-6 days of finasteride follow-up treatment. Finasteride alone reduced DHT, on the average, by 68.7% (SE = 3.4%). Addition of MK-386 suppressed DHT by 89.5% (SE = 1.4%) relative to baseline (P < 0.01 vs. effect of finasteride alone). Small increases in serum T were observed with finasteride alone and in combination with MK-386 (approximately 10% and 19%, respectively). These data are consistent with selective 5 alpha R type 1 inhibition in man by MK-386 and the prediction that types 1 and 2 5 alpha R account for all, or nearly all, of circulating DHT. Further clinical trials are needed to assess the therapeutic utility of type 1 5 alpha R inhibition as well as that of combined inhibition of types 1 and 2 5 alpha R.

Plasma concentrations and effect on testosterone metabolism after single doses of MK-0434, a steroid 5 alpha-reductase inhibitor, in healthy subjects

A four-period, two-panel, single-rising-dose study (0.1-100 mg) was conducted in healthy males to investigate the pharmacodynamics, tolerability and pharmacokinetics of MK-0434, a steroid 5 alpha-reductase inhibitor. MK-0434 was associated with a significant reduction in dihydrotestosterone, which was maximal at 24 h and maintained through 48 h post treatment. The maximum reduction was approximately 50% and occurred at all doses above 5 mg (10, 25, 50 and 100 mg). MK-0434 appeared to have no effect on serum testosterone at these single doses. Rising single doses of MK-0434 were associated with an increase in Cmax and AUC but the changes were less than proportional to dose, most likely due to nonlinear absorption. MK-0434 given in single doses up to 100 mg was without significant adverse effects in healthy male volunteers. In summary, MK-0434 is a well-tolerated, potent, orally active 5 alpha-reductase inhibitor in man.

Finasteride, a steroid 5 alpha-reductase inhibitor, does not affect the oxidative metabolism of antipyrine

A single-blind study was conducted to investigate the effect of multiple doses of finasteride, a 5 alpha-reductase inhibitor for the treatment of benign prostatic hyperplasia, on the single-dose pharmacokinetics of antipyrine. Twelve patients with benign prostatic hyperplasia received a total of four single oral doses of 18 mg/kg antipyrine before, during, and after treatment with 10 mg/day of finasteride for 28 days. Finasteride had no effect on antipyrine concentration profiles. There were also no changes in urinary excretion of three principal antipyrine metabolites. A slight increase in renal clearance of antipyrine was observed; however, this is not considered relevant because excretion of unchanged antipyrine represents a minor fraction of total elimination and is not directly related to oxidative metabolism. These results imply that significant interactions between finasteride and drugs metabolized by these cytochrome P-450 enzymes are unlikely.