Several clinical reports have suggested (but not demonstrated) that ketoconazole, a broad-spectrum antifungal drug, may inhibit hepatic oxidative drug metabolism in man. We recently demonstrated that ketoconazole inhibits caffeine and aminopyrine oxidation in the rat; we now study the influence of ketoconazole on theophylline and chlordiazepoxide kinetics in man. These studies were performed before and after varying doses of ketoconazole within the currently accepted therapeutic range. Ketoconazole had no effect on theophylline clearance, whereas the drug impaired chlordiazepoxide clearance from plasma. After a single dose of ketoconazole, there was a 20% decrease in clearance and a 26% decrease in volume of distribution without evidence of inhibition of drug metabolism. These changes apparently were not related to ketoconazole dose. After repetitive dosing with ketoconazole, chlordiazepoxide clearance decreased by 38% and was associated with reduced concentrations of its first oxidative metabolite, N-desmethylchlordiazepoxide. We conclude that ketoconazole inhibits at least one subset of the hepatic mixed-function oxidase system, but is not as general an inhibitor of hepatic oxidative drug metabolism as cimetidine appears to be. For some coadministered drugs, ketoconazole may also have an effect on other kinetic parameters such as volume of distribution. Therefore, we caution that clinically important drug interactions may occur with the concurrent use of ketoconazole.
The multidrug resistance transport protein is a normal constituent of the liver canalicular membrane, although its function has not been defined in vivo. Colchicine, a multidrug resistance substrate, is eliminated mainly by the liver. Cyclosporine reverses multidrug resistance in vitro, presumably by inhibiting the multidrug resistance transporter. This study assesses biliary colchicine elimination and the effect of cyclosporine on this process. After cyclosporine administration biliary colchicine clearance decreased from 11.6 +/- 0.8 to 2.2 +/- 0.4 ml/min.kg (p less than 0.05), and the colchicine bile/plasma ratio decreased from 166 +/- 9 to 38 +/- 5 (p less than 0.05). Cremophor EL (a cyclosporine vehicle) transiently inhibited biliary colchicine clearance and colchicine bile/plasma ratio, but to a much smaller extent than cyclosporine in vehicle. Biliary cyclosporine clearance was 0.122 and 0.024 ml/min.kg after bolus doses of 2 or 10 mg/kg intravenously, respectively. Cyclosporine bile/plasma ratio was 1.3 to 5.2. When cyclosporine was given 16 hr before colchicine infusion, biliary colchicine clearance decreased 39% (p less than 0.05), and colchicine bile/plasma ratio decreased 51% (p less than 0.05). Thus colchicine is actively secreted into bile and will be useful in the study of the multidrug transporter in vivo. Cyclosporine profoundly inhibits colchicine secretion into bile but is itself mainly metabolized rather than secreted. If competition for a common carrier is the basis for the interaction, then cyclosporine represents a drug that binds to but is not transported by the canalicular transporter.
Recent work has shown that colchicine may benefit patients with primary biliary or alcoholic cirrhosis. However, very little is known about its pharmacokinetics in the presence of impaired liver function. To study this we examined the effects of three models of experimental liver dysfunction and one of cytochrome P-450 inhibition on colchicine elimination in the rat. The models of experimental liver dysfunction included bile duct ligation (with sham-operated controls), alpha-naphthylisothiocyanate-induced intrahepatic cholestasis and galactosamine-induced diffuse hepatocellular necrosis. The control group had a colchicine clearance of 77.33 ml/min.kg +/- 8.27 ml/min.kg, a half-life of 16.68 min +/- 0.97 min and a volume of distribution of 1.84 L/kg +/- 0.15 L/kg. Cimetidine administration, 120 mg/kg intraperitoneally 15 min before colchicine administration, caused clearance to decrease by 32% (p less than 0.05) and half-life to increase by 38% (p less than 0.05). Volume of distribution did not change. At 48 hr after bile duct ligation, colchicine clearance decreased by 84% (p less than 0.05), terminal half-life increased to 513.7 min +/- 106.6 min (p less than 0.05) and volume of distribution increased by 175% (p less than 0.05). Colchicine pharmacokinetics in sham-operated rats were not statistically different from the above mentioned controls.(ABSTRACT TRUNCATED AT 250 WORDS)
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