The effects of cholestyramine and colestipol on the absorption of diclofenac in man.

The effect of oral administration of the non-absorbable anion-exchange resins cholestyramine and colestipol hydrochloride on the absorption of diclofenac in man was studied. Adsorption studies in vitro were also performed. In a randomized crossover study consisting of three phases, single doses of water suspensions of colestipol hydrochloride (10 g), or cholestyramine (8 g), or water only were given to six healthy male volunteers immediately following ingestion of diclofenac (100 mg). After dosing, serial blood samples were collected for a period of 8 hours. Plasma harvested from blood was analyzed for diclofenac by a sensitive and accurate high-performance liquid chromatographic method. The area under the plasma concentration-time curve was moderately (33%, p < 0.05) reduced by colestipol, and greatly reduced (62%) by cholestyramine. The maximum plasma concentration was reduced (58%) by colestipol and even more (75%) by cholestyramine treatment. The in-vitro adsorption studies showed that colestipol has a weaker capacity for adsorption of diclofenac compared to cholestyramine. The in-vivo data suggest a reduction of diclofenac bioavailability when colestipol or cholestyramine is administered concomitantly.