To maintain or improve the patient's ability to carry out activities of daily living (ADL's). More info: Levodopa is now available only in combination preparations, either levodopa/carbidopa or levodopa/carbidopa/entacapone. Only a small fraction of each dose reaches the brain. Most is metabolized in the periphery, primarily by decarboxylase enzymes and to a lesser extent by COMT. Peripheral decarboxylases convert levodopa into dopamine, an active metabolite. In contrast, COMT converts levodopa into an inactive metabolite. Like the enzymes that decarboxylate levodopa within the brain, peripheral decarboxylases work faster in the presence of pyridoxine. Because of peripheral metabolism, less than 2% of each dose enters the brain if levodopa is given alone. For this reason, levodopa is now available only in combination preparations with either carbidopa or carbidopa and entacapone. These additional agents decrease the amount of decarboxylation in the periphery so that more of the drug can enter the central nervous system (CNS)