The clinical picture and plasma levodopa metabolite profile of parkinsonian nonresponders. Treatment with levodopa and decarboxylase inhibitor.

Three parkinsonian patients who were nonresponders to levodopa treatment did not improve when shifted to levodopa-decarboxylase inhibitor combination but, instead, experienced involuntary movements. Their plasma levodopa and metabolite profiles showed unusually high baseline 3-0-methyldopa concentrations that further increased significantly during the decarboxylase inhibitor regimen. All patients had 3-0-methyldopa to levodopa ratios greater than 1, even two hours after therapy. Patients who are responders to levodopa-decarboxylase inhibitor combination or to levodopa alone had 3-0-methyldopa to levodopa ratios of less than 1. We discuss the role of 3-0-methyldopa as a metabolite and the significance of the 3-0-methyldopa to levodopa ratio as a predictor of patients' response to levodopa.