Chronopharmacology of amlodipine in rats.

The present study was undertaken to examine whether plasma concentrations of amlodipine, a calcium antagonist, and its diuretic effects vary with the time of dosage. Pharmacokinetic study; 20 mg/kg of amlodipine was given orally to rats at 10 am (day trial) or 10 pm (night trial), and blood samples were obtained during a 24-hour period. Pharmacodynamic study; two doses (10 and 20 mg/kg) of amlodipine were given orally at 10 am or 10 pm by a cross-over design, and urine was collected for 12 hours after dosage. Rats were maintained under condition of light from 7 am to 7 pm. The following results were obtained; The tmax of amlodipine was shorter and the Cmax was greater in the night trial than in the day trial. Its diuretic effects were greater in the night trial. These results suggest that the pharmacokinetic and pharmacodynamic profiles of amlodipine vary with its time of dosage.