Comparative effectiveness of two extracerebral DOPA decarboxylase inhibitors in Parkinson disease

In four patients with Parkinson disease, we compared carbidopa combined with levodopa (Sinemet) and benserazide combined with levodopa (Madopar). All of these patients had responded to treatment, first with levodopa and then with Sinemet; after 6 years two continued to show a good response, while two developed marked "on-off" phenomena. Clinically, Sinemet and Madopar were similar; however, DOPA levels were higher, but with a shorter half-life, on Madopar. The higher DOPA levels may have been offset by the shorter half-life, resulting in no clinical change. DOPA levels were lower and half-life was shorter in patients with on-off phenomena. These differences may be responsible in part for the on-off phenomena.