Plasma levodopa, dopamine and therapeutic response following levodopa therapy of Parkinsonian patients.

In a double blind placebo controlled study of 6 Parkinsonian patients given a single dose of oral levodopa, the plasma levodopa and dopamine as measured by a radioenzymatic method both correlated with clinical improvement. There was a closer correlation with plasma dopamine than with plasma levodopa and it is proposed that peripheral decarboxylation may reflect central decarboxylation.