Effect of trikatu, an Ayurvedic prescription, on the pharmacokinetic profile of rifampicin in rabbits.

The effect of single and multiple doses of a herbal preparation trikatu, an Ayurvedic prescription, on the bioavailability and pharmacokinetics of rifampicin was studied in rabbits. Rabbits (n = 10) were administered a single dose of rifampicin (24 mg/kg, p.o.) alone or in combination with a single dose of trikatu (500 mg/kg, p.o.). The study had a cross over design with a washout period of 7 days. In the other study, six rabbits were administered a single dose of rifampicin (24 mg/kg, p.o.) before and after multiple doses of trikatu (500 mg/kg x 7d, p.o.). In both studies, blood samples were collected at 0, 0.5, 1, 1.5, 2, 4, 6, 9 and 12 h after drug administration and assayed for rifampicin. In animals treated with single dose of trikatu there was a significant decrease in the peak plasma concentration (Cmax) of rifampicin (P < 0.05). Multiple doses of trikatu also reduced the Cmax and delayed the Tmax of rifampicin although not to a statistically significant level. Other pharmacokinetic parameters of rifampicin were not significantly altered. Our results suggest that coadministration of trikatu does not influence the extent of bioavailability (AUC0-infinity) but reduces the rate of bioavailability (Cmax) of rifampicin. And this latter effect may reduce the efficacy of rifampicin therapy.