The inhibition of soluble catechol-O-methyl-transferase (S-COMT) in red blood cells (RBCs) by entacapone, and the pharmacokinetics of entacapone after single oral (5-800 mg) and i.v. (25 mg) doses have been examined in an open study in 12 healthy young male volunteers. Oral entacapone dose-dependently decreased the activity of S-COMT in RBCs with a maximum inhibition of 82% after the highest dose (800 mg). The inhibition of S-COMT in RBCs was reversible and the activity recovered within 4-8 h. Entacapone showed linear pharmacokinetics over the dose range studied: Cmax and AUC were correlated with the dose of the drug. Oral absorption of entacapone was fast, with a tmax ranging from 0.4 to 0.9 h, depending on the dose. Systemic availability of entacapone varied between 30 and 46%. Entacapone was rapidly eliminated by metabolism with a half-life of 0.27-0.30 h after oral doses of 5 to 50 mg. After doses from 100 to 800 mg the disposition was best described by two phases with a t1/2 alpha of 0.27-0.37 h and t1/2 beta of 1.59-3.44 h. Over the dose range studied, the single oral and i.v. doses of entacapone were well tolerated. No haematological, biochemical or haemodynamic adverse effects were seen. The results show that entacapone is an orally effective and reversible COMT inhibitor in man and has simple, linear pharmacokinetics.

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Objectives To compare plasma levodopa concentrations after repeated doses of levodopa/carbidopa/entacapone (LCE) and levodopa/carbidopa (LC). Methods Open-label, randomized, two-period, activecontrolled, cross-over study with four dosing regimens: groups I and II (healthy volunteers and Parkinson's disease patients) received levodopa 100 mg or 150 mg four times daily, respectively, and groups III and IV (healthy volunteers) received the same strengths of levodopa five times daily. Pharmacokinetic (PK) parameters determined for levodopa included C min , C max , C max −C min , AUC, t 1/2 , and t max .Results In healthy volunteers and PD patients, mean trough levels (C min ), C max , and AUC of levodopa were, in general, significantly higher during LCE compared to LC administration. Compared to C min , C max , and AUC, differences between the treatments in variability of levodopa concentrations (C max −C min ) were less consistent. Conclusions The present results on the differences in levodopa PK between LCE and LC provide a basis to evaluate the relationship of levodopa PK and the induction of motor complications in an on-going study in early Parkinson's disease using similar dosing regimens.

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Objectives-Entacapone is a specific, potent, peripherally acting catechol-Omethyltransferase (COMT) inhibitor. It has been shown to improve the bioavailability of plasma levodopa and extend its clinical eVect when used as an adjunct to standard levodopa preparations, but there is little experience of the eVect of entacapone on controlled release levodopa preparations. (J Neurol Neurosurg Psychiatry 2000;68:589-594) Methods