Metabolism of Levodopa in Patients With Parkinson's Disease

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Abstract
The distribution of carbon 14 labeled levodopa and its metabolites was examined in six patients with Parkinson's disease after oral dosage. Levodopa is well absorbed giving maximum plasma concentrations one to two hours after dosage. Measurable levodopa is in plasma for four to six hours after a single dose. At maximum levels, however, levodopa constituted only 10% of plasma radioactivity. Small amounts of radioactivity were found in the cerebrospinal fluid two hours after dosage (partly as homovanillic acid), while 85% of the dose was recovered in urine in 24 hours. Less than 1% of the dose is recovered in the urine as unchanged levodopa. Simultaneous feeding of milk to one subject apparently delayed absorption of levodopa and may have allowed more extensive degradation of the drug in the gastrointestinal tract.