Although levodopa is a natural body substance, it is also a new drug, and as such, information is needed on the extent and rate of absorption, the distribution in the body, and the mechanisms and rate of elimination. Furthermore, the desired actions in the brain and the central and peripheral side effects appear to be due to one or more biotransformation products rather than to levodopa itself. The current hypothesis of the mechanism of action of levodopa holds that parkinsonism is due to a deficiency of the dopaminergic neurones in the substantia nigra which terminate in the corpus striatum.1 Dopamine itself cannot be used in treatment because of its inability to cross the blood-brain barrier. However, levodopa, an amino acid, enters the brain and is readily decarboxylated to dopamine. Thus, the metabolism of levodopa is of great clinical significance.
In our laboratories, absorption and metabolism studies have been conducted