Peripheral pharmacokinetics of levodopa in untreated, stable, and fluctuating parkinsonian patients.

We compared the pharmacokinetics of oral and IV infusions of levodopa in untreated, stable, and fluctuating patients pretreated with carbidopa. After oral dosing, mean peak plasma levodopa levels, time to peak level concentration after oral levodopa, and area under the curve were similar in all groups. Absorption was proportional to dose. Plasma elimination half-lives, clearance rates, and volumes of distribution after levodopa infusions were similar in all groups. 3-O-Methyldopa levels were similar in stable and fluctuating subjects. We conclude that the peripheral pharmacokinetics of levodopa do not differ between untreated, stable, and fluctuating patients, and that altered peripheral kinetics of the drug are unlikely to explain the development of the fluctuating state.