tolcapone

Tolcapone, sold under the brand name Tasmar, is a medication used to treat Parkinson's disease (PD). It is a selective, potent and reversible nitrocatechol-type inhibitor of the enzyme catechol-O-methyltransferase (COMT). It has demonstrated significant liver toxicity, which has led to suspension of marketing authorisations in a number of countries.

Tolcapone appears to be peripherally selective, but can still cross into the brain in significant amounts and has been found to inhibit COMT centrally as well. In comparison with entacapone, another nitrocatechol COMT inhibitor, tolcapone has a longer half life (2.9 hours vs. 0.8 hours) and can better penetrate into the brain, acting both in the central nervous system and in the periphery. However, entacapone is less toxic for the liver.