Imipramine-mediated interference with levodopa absorption from the gastrointestinal tract in man.

The effect of imipramine on the absorption of a single dose of levodopa was studied in male volunteers. By delaying gastric emptying and retarding delivery to intestinal absorptive sites, imipramine interfered with the absorption of levodopa. This action caused by the anticholinergic effect of imipramine. The retardation of transit of levodopa also caused the elaboration of therapeutically inactive metabolites of levodopa in the gastrointestinal tract. Antidepressants and levodopa are often given together, and this combination may interfere with the absorption and efficacy of levodopa in the treatment of Parkinson's disease.