Pharmacokinetics and metabolism of antipyrine (phenazone) after intravenous and oral administration.

To 12 healthy male volunteers, 6 smokers and 6 non-smokers, 10 mg/kg antipyrine (phenazone) was administered i.v. and p.o. in random order. Following i.v. administration, antipyrine kinetics could be described best by an open two-compartment model. Absolute bioavailability of an aqueous solution of antipyrine was on average 97%. Antipyrine half-life in smokers was significantly shorter (mean 9.7 h) as compared to non-smokers (mean 11.7 h). Smokers excreted significantly more 3-hydroxymethyl-antipyrine (17.2 +/- 2.4 vs. 14.2 +/- 1.9%) than non-smokers, and clearance to this metabolite was significantly increased in smokers. In addition, cumulative urinary excretion of 4-hydroxy-antipyrine, norantipyrine and 3-hydroxymethyl-antipyrine was on average higher in smokers (77.1 +/- 5.0%) as compared to non-smokers (69.5 +/- 10.8%). Thus, 3-hydroxymethyl-antipyrine formation is induced in smokers.