Micafungin is an antifungal agent metabolized by arylsulfatase with secondary metabolism by catechol-O-methyltransferase. The objectives of this study were to estimate the pharmacokinetic parameters and plasma protein binding of micafungin in volunteers with moderate hepatic dysfunction (n = 8), volunteers with creatinine clearance < 30 mL/min (n = 9), and matched controls (n = 8 and n = 9, respectively). Single-dose micafungin pharmacokinetics were estimated using noncompartmental techniques. There was a statistically lower area under the observed micafungin concentration-time curve (AUC) from time 0 to infinity for subjects with moderate hepatic dysfunction as compared to control subjects (97.5 +/- 19 microg.h/mL vs 125.9 +/- 26.4 microg.h/mL, P = .03), although there was no difference in micafungin weight-adjusted clearance (10.9 +/- 1.7 mL/h/kg vs 9.8 +/- 1.8 mL/h/kg, P = .2). The difference in area under the concentration-time curve may be explained by the differences in body weight between subjects and controls. Renal dysfunction did not alter micafungin pharmacokinetics.

Isavuconazole, the active moiety of the water-soluble prodrug isavuconazonium sulfate, is a triazole antifungal agent used for the treatment of invasive fungal infections. The objective of this analysis was to develop a population pharmacokinetic (PPK) model to identify covariates that affect isavuconazole pharmacokinetics and to determine the probability of target attainment (PTA) for invasive aspergillosis patients. Data from nine phase 1 studies and one phase 3 clinical trial (SECURE) were pooled to develop the PPK model (NONMEM, version 7.2). Stepwise covariate modeling was performed in Perl-speaks-NONMEM, version 3.7.6. The area under the curve (AUC) at steady state was calculated for 5,000 patients by using Monte Carlo simulations. The PTA using the estimated pharmacodynamic (PD) target value (total AUC/MIC ratio) estimated from in vivo PD studies of invasive aspergillosis over a range of MIC values was calculated using simulated patient AUC values. A two-compartment model with a Weibull absorption function and a first-order elimination process adequately described plasma isavuconazole concentrations.

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This report describes the phase 1 trials that evaluated the metabolism of the novel triazole antifungal isavuconazole by cytochrome P450 3A4 (CYP3A4) and isavuconazole's effects on CYP3A4‐mediated metabolism in healthy adults. Coadministration of oral isavuconazole (100 mg once daily) with oral rifampin (600 mg once daily; CYP3A4 inducer) decreased isavuconazole area under the concentration‐time curve (AUCτ) during a dosing interval by 90% and maximum concentration (Cmax) by 75%. Conversely, coadministration of isavuconazole (200 mg single dose) with oral ketoconazole (200 mg twice daily; CYP3A4 inhibitor) increased isavuconazole AUC from time 0 to infinity (AUC0‐∞) and Cmax by 422% and 9%, respectively. Isavuconazole was coadministered (200 mg 3 times daily for 2 days, then 200 mg once daily) with single doses of oral midazolam (3 mg; CYP3A4 substrate) or ethinyl estradiol/norethindrone (35 μg/1 mg; CYP3A4 substrate). Following coadministration, AUC0‐∞ increased 103% for midazolam, 8% for ethinyl estradiol, and 16% for norethindrone; Cmax increased by 72%, 14%, and 6%, respectively. Most adverse events were mild to moderate in intensity; there were no deaths, and serious adverse events and adverse events leading to study discontinuation were rare. These results indicate that isavuconazole is a sensitive substrate and moderate inhibitor of CYP3A4.

This report summarizes phase 1 studies that evaluated pharmacokinetic interactions between the novel triazole antifungal agent isavuconazole and the immunosuppressants cyclosporine, mycophenolic acid, prednisolone, sirolimus, and tacrolimus in healthy adults. Healthy subjects received single oral doses of cyclosporine (300 mg; n = 24), mycophenolate mofetil (1000 mg; n = 24), prednisone (20 mg; n = 21), sirolimus (2 mg; n = 22), and tacrolimus (5 mg; n = 24) in the presence and absence of clinical doses of oral isavuconazole (200 mg 3 times daily for 2 days; 200 mg once daily thereafter). Coadministration with isavuconazole increased the area under the concentration‐time curves (AUC0–∞) of tacrolimus, sirolimus, and cyclosporine by 125%, 84%, and 29%, respectively, and the AUCs of mycophenolic acid and prednisolone by 35% and 8%, respectively. Maximum concentrations (Cmax) of tacrolimus, sirolimus, and cyclosporine were 42%, 65%, and 6% higher, respectively; Cmax of mycophenolic acid and prednisolone were 11% and 4% lower, respectively. Isavuconazole pharmacokinetics were mostly unaffected by the immunosuppressants. Two subjects experienced elevated creatinine levels in the cyclosporine study; most adverse events were not considered to be of clinical concern. These results indicate that isavuconazole is an inhibitor of cyclosporine, mycophenolic acid, sirolimus, and tacrolimus metabolism.

Cyclosporine is a marketed immunosuppressive agent and a known substrate for CYP3A. Micafungin is an antifungal agent and a mild inhibitor of CYP3A-mediated metabolism in vitro. The objectives of this study were to evaluate the pharmacokinetics of cyclosporine and micafungin before and with concomitant administration. The pharmacokinetics of single-dose oral cyclosporine (5 mg/kg) were estimated on days 1, 9, and 15 (n = 27). Subjects received micafungin (100 mg/d over 1 hour) on days 7, 9, and 11 through 15. Micafungin pharmacokinetics were estimated on days 7, 9, and 15. Mean apparent oral cyclosporine clearances were estimated to be 645+/-236 mL/h/kg, 546+/-101 mL/h/kg (P = .01), and 540+/-104 mL/h/kg (P = .02) for days 1, 9, and 15, respectively. Micafungin appears to be a mild inhibitor of cyclosporine metabolism.

Patients undergoing treatment with immunosuppressant drugs following solid organ or hematopoietic stem cell transplantation are at particular risk for development of serious infections such as invasive aspergillosis. Four triazole antifungal drugs, voriconazole, posaconazole, itraconazole, and isavuconazole, are approved to treat invasive aspergillosis either as first-or second-line therapy. All of these agents are inhibitors of cytochrome P450 3A4, which plays a key role in metabolizing immunosuppressant drugs such as cyclosporine, tacrolimus, and sirolimus. Thus, co-administration of a triazole antifungal drug with these immunosuppressant drugs can potentially increase plasma concentrations of the immunosuppressant drugs, thereby resulting in toxicity, or upon discontinuation, inadvertently decrease the respective concentrations with increased risk of rejection or graft-versus-host disease. In this article, we review the evidence for the extent of inhibition of cytochrome P450 3A4 by each of these triazole antifungal drugs and assess their effects on cyclosporine, tacrolimus, and sirolimus. We also consider other factors affecting interactions of these two classes of drugs. Finally, we examine recommendations and strategies to evaluate and address those potential drug-drug interactions in these patients. Invasive aspergillosis (IA) is the most common IFD in HSCT recipients and has been reported to account for between 40% and 60% of cases. 4,5 In SOT recipients, IA is the second most common IFD overall, but the leading IFD in lung transplant recipients. 6 Mortality from IA is substantial in both patient populations. In prospective, multicenter, observational studies, the overall 6-week mortality rate among HSCT recipients with IA in North America was 22% 5 and 1-year mortality rate in the United States (US) was 75%. 4 In a separate prospective, multicenter, observational study, the 1-year mortality rate among SOT

Isavuconazole, the active moiety of the water-soluble prodrug isavuconazonium sulfate, is a triazole antifungal agent for the treatment of invasive fungal infections. The purpose of this analysis was to characterize the isavuconazole exposure-response relationship for measures of efficacy and safety in patients with invasive aspergillosis and infections by other filamentous fungi from the SECURE clinical trial. Two hundred thirty-one patients who received the clinical dosing regimen and had exposure parameters were included in the analysis. The primary drug exposure parameters included were predicted trough steady-state plasma concentrations, predicted trough concentrations after 7 and 14 days of drug administration, and area under the curve estimated at steady state (AUCss). The exposure parameters were analyzed against efficacy endpoints that included all-cause mortality through day 42 in the intent-to-treat (ITT) and modified ITT populations, data review committee (DRC)-adjudicated overall response at end of treatment (EOT), and DRC-adjudicated clinical response at EOT. The safety endpoints analyzed were elevated or abnormal alanine aminotransferase, increased aspartate aminotransferase, and a combination of the two. The endpoints were analyzed using logistic regression models. No statistically significant relationship (P > 0.05) was found between isavuconazole exposure and either efficacy or safety endpoints. The lack of association between exposure and efficacy indicates that the isavuconazole exposures achieved by clinical dosing were appropriate for treating the infecting organisms in the SECURE study and that increases in alanine or aspartate aminotransferase were not related to increase in exposures. Without a clear relationship, there is no current clinical evidence for recommending routine therapeutic drug monitoring for isavuconazole.