Plasma levels of levodopa and its main metabolites in parkinsonian patients after conventional and controlled-release levodopa-carbidopa associations.

The paper reports plasma levels of levodopa (LD), its main metabolites [dopamine, dihydroxyphenylacetic acid, homovanillic acid, 3-O-methyldopa (3-O-MD)] and carbidopa in 14 parkinsonian patients first treated with Sinemet and thereafter with Sinemet-CR4. A good relationship was observed between LD plasma levels and pharmacological effects. While the LD area under the curve increased after Sinemet-CR4, the same was not observed with metabolites, except with 3-O-MD. The experiments in volunteer subjects confirmed the increase in 3-O-MD in plasma after Sinemet-CR4. Higher levels were observed also in the CSF with a reduction of LD concentrations. This seems to corroborate the hypothesis of an interference with LD passage through the blood-brain barrier in humans.