Intermittent levodopa therapy in parkinsonism.

Chronic high-dose levodopa therapy in Parkinson's disease is associated with an apparent loss of efficacy and an increased prevalence of side effects which limit its effectiveness. Low-dose alternate-day levodopa provided adequate control of early but not late parkinsonism. Stable clinical responses occurred both on the day of drug administration and on the following day, although plasma levodopa levels were negligible on the day when no drug was given. Alternate-day therapy results in less cumulative dosage and may better preserve existing compensatory striatal activity. Intermittent levodopa therapy needs to be further investigated, as it may lead to effective long-term treatment and an improved therapeutic index.