Interaction of tricyclic antidepressants with cholestyramine in vitro.

The adsorption of amitriptyline, desipramine, doxepin, imipramine, and nortriptyline onto cholestyramine was demonstrated in vitro with use of 1.2 mol/L HCl at 37 degrees C to simulate gastric fluid. Binding to cholestyramine was approximately 80% for each of the tricyclic antidepressants, and this was about the same degree of binding noted with a nonpharmaceutical, non-ionic resin widely used in the diagnostic toxicology laboratory (Amberlite XAD-2). In contrast, five other non-antidepressants (acetaminophen, chlordiazepoxide, procainamide, quinidine, and theophylline) showed only minimal binding to cholestyramine under these conditions. Activated charcoal completely bound all drugs studied. These findings suggest that cholestyramine should be used with caution in patients receiving tricyclic antidepressants. They also suggest that cholestyramine may be a potentially useful adjunctive therapy in treatment of overdose with the tricyclic antidepressants.