Medical Health Encyclopedia

Catechol-O-methyl transferase (COMT) inhibitors increase concentrations of existing dopamine in the brain. Entacapone (Comtan) is the current standard COMT inhibitor. It improves motor fluctuations related to the wearing-off effect and has shown good results in improving on time and reducing the requirements for L-dopa. If the patient does not respond to the drug within three weeks, it should be withdrawn. No one should withdraw abruptly from these drugs.

Side Effects. Side effects include the following:

• Involuntary muscle movements.
• Mental confusion and hallucinations.
• Cramps, nausea, and vomiting.
• Insomnia
• Headache.
• Urine discoloration. (This is a harmless side effect but should be reported.)
• Diarrhea.
• Less commonly, constipation, susceptibility to respiratory infection, sweating, dry mouth.

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Of major concern are reports of a few deaths from liver damage in patients taking tolcapone (Tasmar), another COMT inhibitor. The drug has been taken off the market in many countries and is recommended in the U.S. only for patients who cannot tolerate another other agents. Entacapone does not appear to have the same effects on the liver and does not require monitoring. A 2003 three-year study suggested that the drug is safe and effective over the long term. Still, patients should watch out for symptoms of liver damage, including jaundice (yellowish skin), fatigue, and loss of appetite.

Jaundice is a condition produced when excess amounts of bilirubin circulating in the blood stream dissolve in the subcutaneous fat (the layer of fat just beneath the skin), causing a yellowish appearance of the skin and the whites of the eyes. With the exception of normal newborn jaundice in the first week of life, all other jaundice indicates overload or damage to the liver, or inability to move bilirubin from the liver through the biliary tract to the gut.

Anticholinergic Drugs