Comparison of dopa decarboxylase inhibitor (carbidopa) combined with levodopa and levodopa alone in Parkinson's disease.

A double-blind study comparing the effects of carbidopa and levodopa combined in a single tablet with levodopa alone was undertaken in 50 patients with Parkinson's disease. After 6 months, there was a statistically significant improvement over baseline in total score, rigidity, and tremor only in the patients randomized to carbidopa/levodopa. In addition, 40 percent of the patients treated with carbidopa/levodopa showed obvious clinical improvement (a greater than 50 percent reduction in their total score) over treatment with levodopa alone. However, after 2 years, only 20 percent continued to show this improvement. Nausea, vomiting, and anorexia developed in 56 percent of patients on levodopa but in only 27 percent of patients on carbidopa/levodopa. However, abnormal involuntary movements, observed in 48 percent of patients on levodopa, were present in 77 percent of patients on carbidopa/levodopa. Despite the increase in abnormal involuntary movements, carbidopa/levodopa is more effective than levodopa.