Voriconazole Inhibition of Tacrolimus Metabolism

Abstract
Sir—Voriconazole (Pfizer) is a new triazole antifungal agent used in the management of invasive infections caused by molds such as Aspergillus species, Fusarium species and Scedosporium apiospermum. This agent is known to inhibit the cytochrome P450 (CYP) isoenzymes 3A4, 2C9, and 2C19, and is consequently associated with a number of drug interactions [1]. Preliminary observations have demonstrated that voriconazole significantly increases the trough concentrations of tacrolimus [2]. The manufacturer recommends reducing the daily tacrolimus dose by one-third when it is concurrently administered with voriconazole [3]. We describe a patient who required a 90% reduction in the manufacturer's recommended maintenance dose of tacrolimus.