Skip to main content

Catechol-O-methyl transferase (COMT) Inhibitors

Recently, a new class of enzyme inhibitors, called COMT inhibitors, has been developed. Like carbidopa, COMT inhibitors prevent the breakdown of levodopa. Their main effect is to prolong the duration of action of a dose of levodopa. Since COMT inhibitors do not contain levodopa, they must be taken with levodopa in order to have any benefit. COMT inhibitors may be prescribed when an individual experiences "wearing off," particularly when dopamine agonists (see below) are not tolerated. If involuntary movements (dyskinesias) develop after starting a COMT inhibitor, the dose of levodopa may need to be reduced.

COMT inhibitors and their Preparations

  • Entacapone (Comtan®)--available in the U.S. and many other countries.  200 mg tablets usually given with each dose of levodopa

  • Tolcapone (Tasmar®)--available in the United States, but not Canada or Europe.  100 mg and 200 mg tablets; generally given three times a day

Because liver toxicity has occurred in patients taking tolcapone, it is only indicated for patients whose symptoms are not adequately controlled by other medications (including entacapone). People taking tolcapone must have blood drawn periodically to monitor liver function.

Side Effects

Side effects for both of these medications include diarrhea, vivid dreams, visual hallucinations, drowsiness, urine discoloration (orange) and dyskinesias. Tolcapone has been associated with liver toxicity.

Combined carbidopa, levodopa and entacapone

This preparation combines all 3 medications in one pill, which may be more convenient but may not be as flexible as taking the medications individually.

Doses:

Stalevo® 50: 50 mg levodopa, 12.5 mg carbidopa, and 200 mg entacapone

Stalevo® 75: 75 mg levodopa, 18.75 mg carbidopa, and 200 mg entacapone

Stalevo® 100: 100 mg levodopa, 25 mg caribdopa and 200 mg entacapone

Stalevo® 125: 125 mg levodopa, 31.25 mg carbidopa, and 200 mg entacapone

Stalevo® 150: 150 mg levodopa, 37.5 mg carbidopa, and 200 mg entacapone

Stalevo® 200: 200 mg levodopa, 50 mg carbidopa, and 200 mg entacapone

Side Effects

Side effects of this combined preparation are the same as for levodopa and entacapone and include: diarrhea, vivid dreams, visual hallucinations, drowsiness, urine discoloration and dyskinesias.

Copyright © 2010, The Regents of the University of California