Antipyrine disposition in obesity: evidence for negligible effect of obesity on hepatic oxidative metabolism

Following an overnight fast and 2 days of abstention from caffeine, a single 1.0-g oral dose of antipyrine was administered to 20 obese but otherwise healthy subjects (group A) and 11 healthy volunteers (group B). Weight, Body Mass Index (BMI) and % of Ideal Body Weight (IBW) were significantly greater in the obese than in the lean group. (Mean 110.4 vs 62.7 kg; 38.5 vs 22.3 kg · m^-2 and 181vs 106 % respectively). In a subgroup of 6 obese subjects (group C) antipyrine was given again 11.3 months later after a 29.8 kg mean weight loss. Antipyrine apparent volume of distribution (V) and elimination half-life (t_1/2) were significantly greater in the obese than in the lean group (V 49.9 vs 34.3 l respectively; t_1/2 15.5 vs 12.0 h respectively), but its clearance rate (CL_o) values were similar. V corrected for total body weight was significantly reduced in group A than in group B (0.45 vs 0.55 l · kg^-1 respectively). Stratified comparison of antipyrine pharmacokinetics between obese and lean subjects according to age, gender and smoking habits did not alter the overall results. In group C, weight reduction was associated with a significant decrease in antipyrine V (from 51.8 to 47.5 l) and t_1/2 (from 15.1 to 12.7 h), and a non-significant increase in antipyrine CL_o. We conclude that in severely obese subjects, antipyrine total V is mildly increased but V corrected for total body weight is significantly decreased. In addition, obesity is associated with a slight prolongation of antipyrine t_1/2 whereas its CL_o is unaltered. These findings may indicate that obesity, even in its extreme form, has a negligible effect on the oxidative metabolic capacity of the liver.