Sinemet and the treatment of Parkinsonism.

Sinemet (a combination of levodopa with carbidopa, a dopa-decarboxylase inhibitor) has replaced levodopa for early treatment of parkinsonism. The blocking of the systemic uptake of dopamine has eliminated the previous complications of nausea, vomiting, and cardiac and respiratory arrhythmias; pyridoxine need not now be avoided. However, the earlier appearance of abnormal involuntary movements, hallucinations, occasional psychosis, and a dopa-resistant state limits treatment efficacy. In all-over experience the combination drug offers the best relief for rigidity and akinesia. It has improved the quality of life and reduced mortality by one half. The greatest benefits appear in the first 3 years; then complications set in. The relation of complications to dosage is now better understood, and the ratio of dopa-decarboxylase inhibitor to levodopa inhibitor to levodopa of 1:4 is better than the previous 1:10. Levodopa with or without dopa decarboxylase is not a cure for parkinsonism. Some agonist drugs (bromocryptine, lisuride) are showing promise in the testing stage. The evolving knowledge about neurotransmitters and peptide messengers offers hope for the growing number of patients with parkinsonism.