Catechol-O-methyltransferase inhibitors versus active comparators for levodopa-induced complications in Parkinson's disease.

As Parkinson's disease progresses the control of the symptoms often requires the addition of other drugs to levodopa. The principle aim of COMT inhibitor therapy is to increase the duration of effect of the levodopa dose and thus reduce the time patients spend in the relatively immobile 'off' phase.