Influence of feeding and analytical method on the bioequivalence of a racemic drug undergoing enantioselective enterohepatic recycling.

Two crossover bioequivalence trials of an enantioselectively enterohepatic recycled drug, carprofen, were conducted in dogs with the same racemic oral formulation to determine: (i) the influence of feeding patterns, and (ii) the effect of the analytical method (enantioselective vs non-enantioselective) on the statistical power of the trials. The first trial was conducted with a standard feeding protocol and the second with a special feeding protocol selected to ensure constant biliary flow into the duodenum. Using a non-enantioselective technique, 90% confidence intervals provided conclusions of bioequivalence in 100% of the cases for both area under the plasma concentration versus time curve (AUC) and maximum plasma drug concentration (Cmax) with the special feeding protocol, but only 50% for AUC and 13% for Cmax with the standard feeding protocol, suggesting that a feeding pattern that diminishes plasma drug concentration rebound for an enterohepatically recycled drug increases the power of a bioequivalence trial. Whatever the feeding protocol, an enantioselective method decreased the power of the trials for AUC but increased the power of the trials for Cmax. For an enterohepatically recycled drug, feeding pattern can influence the power of a bioequivalence trial, and the analytical technique that provides the greatest power depends on the assessed bioequivalence parameter and the feeding pattern.

Plasma exogenous creatinine clearance test in dogs: comparison with other methods and proposed limited sampling strategy.

Plasma clearance of creatinine was evaluated for assessment of glomerular filtration rate (GFR) in dogs. In 6 healthy dogs (Experiment 1), we determined 24-hour urine clearance of endogenous creatinine, plasma, and urine clearances of exogenous creatinine administered at 40, 80, and 160 mg/kg in a crossover design (linearity study), plasma iothalamate clearance, and plasma and urine clearances of 14C-inulin. In Experiment 2, plasma creatinine and iothalamate clearances were compared, and a linearity study was performed as for Experiment 1 in 6 dogs with surgically induced renal impairment. Experiment 3 compared plasma creatinine clearance with plasma iothalamate clearance before and 3 weeks after induction of moderate renal impairment in 6 dogs. Plasma creatinine clearances were calculated by both noncompartmental and compartmental analyses. In Experiment 1, plasma inulin clearance was higher (P < .001) than other clearance values. Plasma creatinine clearances at the 3 dose rates did not differ from urine inulin clearance and each other. In Experiment 2, plasma creatinine clearances were about 14% lower than plasma iothalamate clearance (P < .05). In Experiment 3, decreases in GFR assessed by plasma clearances of iothalamate and creatinine were similar. Renal failure decreased the daily endogenous input rate of creatinine by 25%. Limiting sampling strategies for optimizing GFR calculation were proposed, allowing an error lower than 6.5% with 4 blood samples. These results suggest that determination of plasma creatinine clearance by a noncompartmental approach offers a reliable, inexpensive, rapid, and convenient means of estimating GFR in routine practice.