Catechol-O-methyltransferase (COMT) inhibitors in Parkinson's disease.

Catechol-O-methyltransferase (COMT) inhibitors are a new therapeutic option in the treatment of patients with Parkinson's disease. COMT inhibitors act by extending the duration of action of levodopa, thus improving the amount of time a patient can experience benefit from levodopa. COMT inhibitors are only used in conjunction with levodopa. They do have a propensity to augment dopaminergic effects, such that levodopa doses might need to be adjusted downward. Other side effects of COMT inhibitors include diarrhea and liver function abnormalities. Due to the latter, recent guidelines have been developed to monitor patients on tolcapone for this rare side effect, and these guidelines will be discussed. This article also provides representative case histories for the appropriate use of COMT inhibitors that illustrate how these drugs can be used to manage patients with a fluctuating response to levodopa.