Pharmacokinetics of isavuconazole in healthy cats after oral and intravenous administration

Abstract

Background: Isavuconazole is a triazole antifungal drug that has shown good efficacy in human patients. Absorption and pharmacokinetics have not been evaluated in cats. Objectives: To determine the pharmacokinetics of isavuconazole in cats given a single IV or PO dose. Animals: Eight healthy, adult research cats. Methods: Four cats received 100 mg capsules of isavuconazole PO. Four cats received 5 mg/kg isavuconazole solution IV. Serum was collected at predetermined intervals for analysis using ultra-high performance liquid chromatography-tandem mass spectrometry. Data were analyzed using a 2-compartment uniform weighting pharmacokinetic analysis with lag time for PO administration and a 2 compartment, 1/y2 weighting for IV administration. Predicted 24 and 48-hour dosing intervals of 100 mg isavuconazole administered PO were modeled and in vitro plasma protein binding was assessed. Results: Both PO and IV drug administration resulted in high serum concentrations. Intravenous and PO formulations of isavuconazole appear to be able to be used interchangeably. Peak serum isavuconazole concentrations occurred 5 ± 3.8 hours after PO administration with an elimination rate half-life of 66.2 ± 55.3 hours. Intersubject variability was apparent in both the PO and IV groups. Two cats vomited 6 to 8 hours after PO administration. No adverse effects were observed in the IV group. Oral bioavailability was estimated to be approximately 88%. Serum protein binding was calculated to be approximately 99.0% ± 0.03%. Conclusions and Clinical Importance: Isavuconazole might prove to be useful in cats with fungal disease given its favorable pharmacokinetics. Additional studies on safety, efficacy, and tolerability of long-term isavuconazole use are needed.