Inhibition of antipyrine metabolism by interferon

Antipyrine clearance was measured before and 1 day after administration of a single intramuscular dose of recombinant human leukocyte alpha A interferon. In the nine patients studied, antipyrine clearance was reduced after interferon from 0.49 (0.21-1.13) ml kg-1 min-1 (median (range)) to 0.41 (0.20-1.07) ml kg-1 min-1, P less than 0.01. In individual patients, the decrement in antipyrine clearance was variable, ranging from 5-47% (median, 16%). This study provides the first direct evidence that interferon inhibits hepatic oxidative drug metabolism in humans and alerts clinicians to the possibility of potentially toxic drug-drug interactions.