Sites of first-pass bioactivation (hydrolysis) of orally administered zofenopril calcium in dogs

Pharmacokinetic assessment of the sites of first-pass metabolism of BMS-181101, an antidepressant agent, in rats

The relative contribution of the gut and the liver to the first-pass metabolism of BMS-181101 (3-[3-[4-(5-methoxy-4-pyrimidinyl)-1-piperazinyl]propyl]-5-fluoro-1H-ind ole dihydrochloride), a potential antidepressant agent, has been evaluated in rats. Nine male Sprague-Dawley rats were divided into three groups of three and each rat received a single 20 mg kg(-1) dose of [14C]BMS-181101 via a 30 min constant-rate intravenous infusion, a 30-min constant-rate intraportal infusion or oral gavage. Serial blood samples were collected for 8 h after dosing and plasma was analysed for unchanged BMS-181101 and total radioactivity. Extraction ratios for BMS-181101 by the gut and liver were calculated on the basis of ratios of the area under the plasma BMS-181101 concentration-time curve. The gut had a high intrinsic capacity for metabolizing BMS-181101-extraction ratios were 93% and 10% for the gut and liver, respectively. After oral administration BMS-181101 is sequentially exposed to the gut then the liver. As a result, the contribution of the gut to the overall first-pass effect (ca. 93%) was significantly greater than that of the liver (ca. 0.7%). The estimated total first-pass effect of 94% for BMS-181101 in rats is in excellent agreement with the observed absolute oral bioavailability of 6%. These results clearly illustrate the importance of metabolic activity in the gut for orally administered BMS-181101.

Prodrugs of BMS-183920: metabolism and permeability considerations

The oral bioavailability of BMS-183920, a diacidic, potent angiotensin II receptor antagonist, is low in rats (approximately 11%). In vivo studies in bile duct-cannulated rats indicated that BMS-183920 was metabolically stable and that the low bioavailability was due to incomplete intestinal absorption. Five acyl-ester prodrugs were synthesized which were 5-15 times more permeable than BMS-183920 through Caco-2 cells. However, limited studies in rats indicated that the oral bioavailability of BMS-183920 was improved only 2-fold, in the best case. The lack of a substantial increase in bioavailability was apparently due to presystemic prodrug hydrolysis or metabolism via N-glucuronidation. Bioavailability of BMS-183920 after oral dosing of a tetrazole-ester prodrug averaged 37%, the most significant improvement within this prodrug series. Interestingly, in vitro studies indicated that the tetrazole-ester prodrug was a substrate for glucuronosyl transferase; however, its rate of bioactivation (hydrolysis) was sufficiently high to provide a substantial increase in bioavailability of BMS-183920. Therefore, while prodrug modification of BMS-183920 improved Caco-2 cell permeability and oral absorption in vivo, the relative extents of hydrolysis (bioactivation) vs metabolism of the prodrug determined whether a substantial improvement in bioavailability was achieved.

Temperature, pH and agitation rate as dissolution test discriminators of zofenopril calcium tablets

Comparative in vitro dissolution studies were performed on several tablet batches of zofenopril calcium, an ACE inhibitor, to determine if they could be differentiated on the basis of their release rates. The samples included six batches produced at Site 1 and one batch produced at Site 2. Using regular dissolution conditions (USP paddle method at a 50-rpm agitation speed in phosphate buffer, pH 7.5, at 37 degrees C), release rates of all the tablet batches were similar. By independently altering one of the dissolution test parameters, either a lower pH or a slower agitation rate, discrimination between the Site 1 and Site 2 tablets was enhanced. Discrimination was only slightly enhanced when a lower dissolution medium temperature was used. Tablets made from different polymorphs of zofenopril calcium could not be differentiated by their dissolution profiles, even with the more discriminating conditions. The dissolution profiles of certain other zofenopril calcium tablets (including film-coated vs uncoated tablets, and tablets made with micronized vs unmicronized drug particles) were indistinguishable using a 50-rpm agitation rate, but they could be clearly differentiated using a 40-rpm agitation rate.