The absorption and metabolism of a standard oral dose of levodopa in patients with Parkinsonism.

1 The metabolism of a standard oral dose of levodopa was studied in forty-two patients with Parkinsonism. Plasma levodopa and 3-o-methyldopa concentrations were estimated at intervals for 8 h after ingestion and the concentration of homovanillic acid (HVA) in the lumbar cerebrospinal fluid (CSF) was measured at 8 hours. Clinical responses 3 months after the test were compared with these findings. 2 Although therapeutic benefit correlated significantly with calculated estimates of both plasma levodopa concentration and CSF HVA at optimal levodopa dose, individual values were widely scattered. There was no significant correlation between toxic effects and plasma levodopa or CSF HVA; and 3-o-methyldopa concentrations similarly did not show a significant correlation with either toxic or therapeutic effects. 3 Blood and CSF levels of levodopa or the metabolites measured in this study were not significantly altered by concurrent treatment with either anticholinergic drugs or amantadine nor by previous treatment with levodopa.