Motor fluctuations are a common problem in the long-term treatment of
Parkinson's disease (PD).
Entacapone (
Comtan) is a potent, peripherally acting, reversible and selective inhibitor of
catechol-O-methyltransferase (COMT). Used as an adjuvant to
levodopa therapy,
entacapone slows the elimination of
levodopa by decreasing peripheral conversion to
3-O-methyldopa, increasing central extracellular
levodopa and striatal
dopamine concentrations. Coadministered with
levodopa/
carbidopa or
levodopa/
benserazide, at doses of 200 mg 2 to 10 times daily in patients with end-of-dose fluctuations,
entacapone may increase the duration of clinical response, both after the first single dose and after repeated dosing. At this dosage, it has a time to peak plasma concentration of 1.2 h and an elimination half life of 3.4 h. In two multicentric, long-term (24 weeks), parallel, randomized and placebo-controlled studies,
entacapone increased the duration of 'on' time (by approximately 1 hour daily) and decreased the duration of 'off' time with a concomitant reduction in the mean daily
levodopa dose. In these and other phase III studies,
entacapone was generally well tolerated, with most adverse effects being
dyskinesias and
gastrointestinal disorders. Increased
dyskinesia were generally controlled by reducing
levodopa doses.
Entacapone appears to be a useful adjunct in extending the benefit of each
levodopa dose in PD patients with end-of-dose fluctuations.