Effect of a slow release preparation of levodopa on Parkinson's disease in combination with a peripheral decarboxylase inhibitor.

Plasma concentrations of levodopa were determined after therapeutic oral levodopa-carbidopa doses. The wide fluctuations observed in plasma levodopa levels could be considerably reduced by the addition of a slow release levodopa preparation. This kind of combination medication was given to 15 parkinsonian patients, whose earlier therapy had proved inadequate. With the combination medication, levodopa-carbidopa, on an average 420 mg/42 mg combined with 950 mg of levodopa in slow release form, a statistically significant improvement in parkinsonian signs could be achieved without any worsening of the side effects. The results suggest that parkinsonian patients may tolerate much higher daily levodopa doses if the fluctuations in plasma levels of the drug can be diminished.