Pharmacokinetics, metabolism and biliary and urinary excretion of oral ramipril in man.

In order to evaluate the pharmacokinetics and excretion of ramipril in man, 8 cholecystectomy patients aged between 53 and 68 years received 5 mg ramipril orally as a single dose. All patients had a T-drain inserted to permit bile collection; all gave their informed consent to participate in the trial. Serum samples were collected half-hourly until 2 hours, then hourly until 6 hours, then at 8, 10, 24 and 25 hours after intake. Urine was collected in 2-hour fractions until 8 hours, followed by a 4- and a 12-hour fraction. Bile was collected hourly until 6 hours, followed by a 6- and a 12-hour collecting fraction. Concentrations of ramipril and ramiprilat in serum, and determinations in urine and bile of ramipril, ramiprilat, ramipril glucuronide, ramiprilat glucuronide, diketopiperazine and diketopiperazine acid were made; total amounts excreted were calculated. Peak concentrations of ramiprilat in plasma (8.7 +/- 1.6 ng/ml) were reached after about 8 hours. AUC0-8 and AUC0-24-values were 36.5 and 111.9 ng.h/ml, respectively. Ramiprilat Cmax-concentrations were about 300-fold higher in bile than in plasma, the corresponding difference for ramipril between bile and plasma was about 4-fold. The main fractions excreted in the urine were diketopiperazine acid and ramiprilat amounting to 13.2 +/- 5.6 and 4.4 +/- 2.4%, respectively, of the dose administered. Only a very small fraction of the dose was excreted with urine as unchanged ramipril, on average 0.9 +/- 1.0%. The main fractions excreted in the bile were diketopiperazine acid, ramiprilat glucuronide and diketopiperazine, 9.0 +/- 5.3, 3.4 +/- 4.2 and 2.0 +/- 1.2% in 24 hours, respectively, of the dose administered. Only a negligible fraction of the dose (average 0.1 +/- 0.1%) was excreted with bile as unchanged ramipril. In conclusion, there is strong evidence that circulating ramipril and ramiprilat are eliminated by both the liver and the kidneys. For the patients studied it can be estimated from late collection periods that some 2/3 of circulating ramipril and ramiprilat are eliminated by the kidneys and 1/3 eliminated by the liver.