Antipyrine metabolism is not affected by terbinafine, a new antifungal agent

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Abstract
The potential to inhibit drug metabolism of the new antifungal agent terbinafine has been studied using antipyrine (single oral dose of 10 mg/kg) as a probe drug. In a cross-over study in 8 healthy volunteers, antipyrine was administered prior to, during and after 8 days of oral terbinafine 125 mg b.d. Antipyrine, its major metabolites 4-hydroxyantipyrine (4-OH-AP), 3-hydroxymethylantipyrine (3-OH-CH3-AP) and norantipyrine (Nor-AP) were analyzed by specific HPLC assays in multiple plasma and urine samples. During all three parts of the study, the pharmacokinetics of antipyrine viz. t1/2 (11.7 h), total plasma (38.5 ml·h−1·kg−1) and renal clearance (1.6 ml·h−1·kg−1), and its clearance rates to metabolites (CLM), eg. CLM for 4-OH-AP (12.3 ml·h−1·kg−1), CLM for 3-OH-CH3-AP (4.2 ml·h−1·kg−1) and CLM for Nor-AP (6.7 ml·h−1·kg−1) did not differ from the control values. Thus, all the cytochrome P-450-dependent isozymes involved in the metabolism of antipyrine and many other drugs should not be affected by therapeutic doses of terbinafine.