Metabolism of dopamine prodrug, docarpamine.

Docarpamine is a dopamine prodrug which has been selected from a large number of dopamine derivatives in order to develop an orally effective dopamine. The pharmacokinetics and metabolism after oral administration of docarpamine were studied in rats and dogs. The maximum concentration of free dopamine in plasma after oral administration of docarpamine to rats and dogs was 13 and 4-6 times, respectively, higher than those of dopamine (DA). In the first pass metabolism study in dogs, the main metabolic pathways after oral administration of docarpamine were catechol ester hydrolysis in the small intestine, and amide hydrolysis and conjugation in the liver. Conversion rates from docarpamine to DA in various rat tissue homogenates were in the order of the liver > small intestine > blood. The concentrations of DA conjugate and 3,4-dihydroxyphenylacetic acid in plasma after oral administration of DA to dogs were higher than those of docarpamine. This result indicates that protected groups of the docarpamine molecule suppress the first pass metabolism of orally administered dopamine. In conclusion, the findings of this study suggest that docarpamine can be used as an oral dopamine prodrug. The main first pass metabolism after oral administration of docarpamine are catechol ester hydrolysis in the small intestine, and amide hydrolysis and conjugation in the liver. Free dopamine, which is a pharmacologically active form, is mainly produced in the liver.