Entacapone in combination with standard or controlled‐release levodopa/carbidopa: a clinical and pharmacokinetic study in patients with Parkinson's disease

Abstract

We investigated clinical response and pharmacokinetics of levodopa when entacapone, a catechol O-methyltransferase (COMT) inhibitor, was administered concomitantly with either a standard (Std) or a controlled-release (CR) levodopa/carbidopa preparation to 12 patients with Parkinson's disease. An open cross-over study consisted of the initial study day without entacapone followed by two 10-day treatment periods with a study day at the end of each period. The patients who received entacapone (200 mg t.i.d. or q.i.d.) concomitantly with Std levodopa/carbidopa (200/50 mg t.i.d. or q.i.d.) during the first period received subsequently entacapone with CR levodopa/carbidopa (200/50 mg t.i.d. or q.i.d.), and vice versa. On the study days, the patients took the medication at 8 a.m. and the second dose 6 h later. We evaluated the disability before drug administration and then 1-h intervals for 8 h. Repeated blood samples were taken for analysis of plasma levodopa, 3-O-methyldopa (3-OMD), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), carbidopa, and entacapone. Entacapone decreased significantly the clinical disability with both Std and CR levodopa, slightly more with Std levodopa. The clinical response started earlier with Std levodopa whereas the "on"-time increased by about 1 h, equally with both levodopa preparations. Std levodopa produced 23% higher area under the curve (AUC) of levodopa than the CR preparation, but entacapone increased the AUC approximately equally, 33% with Std and 36% with CR levodopa. Entacapone slightly decreased Cmax of levodopa in combination with Std levodopa, whereas it increased that with CR levodopa. The AUC of 3-OMD was about 20% smaller after Std than after CR levodopa. Entacapone decreased the AUC of 3-OMD by 38-40% with both levodopa preparations. Entacapone did not modify the AUC levels of carbidopa although its bioavailability was less from CR levodopa than from Std levodopa. In three patients levodopa dosage was reduced when on Std levodopa because of nausea. Otherwise, the treatments were well tolerated. The study shows that entacapone is an effective COMT inhibitor when combined with either Std levodopa or CR levodopa.