Success and problems of long-term levodopa therapy in Parkinson's disease.

The patient with Parkinson' disease on chronic levodopa therapy, like the diabetic on insulin, is dependent on the drug. Like the diabetic, the patients with Parkinson's disease may run into problems during long-term treatment. Two have emerged as frequent and serious, an insidious and progressive loss of benefit and the appearance of progessively more severe fluctuations in disability. It is concluded that progression of the underlying pathology of the disease is probably responsible. Discovery of the exact causes for loss of benefit may provide a rational basis for new therapy.