Children
Entacapone safety and efficacy have not been assessed in infants or children. Liver problems
Biliary excretion is the major route of excretion for entacapone. People with liver dysfunction may require additional caution and more frequent liver function monitoring while taking entacapone. Kidney problems
There are no significant considerations for people with poor kidney function taking entacapone. Contraindications
There is a high risk for allergic reactions for people who are hypersensitive to entacapone.Potential limiting conditions to consider before starting entacapone include:
History of allergic reaction to entacapone
History of liver disease, liver dysfunction, or alcoholism
Current or planned pregnancy
Current or planned surgeries

Side effects
The following side effects have been reported by people with Parkinsons disease treated with entacapone:

Abdominal pain
Nausea
Vomiting
Fatigue
Dry mouth
Back ache

Movement problems
The most common side effect of entacapone is movement problems, which occur in 25% of people taking entacapone. This drug may cause or worsen dyskinesia for people with Parkinsons disease treated together with levodopa and carbidopa. In particular, "peak-dose dyskinesias" may occur when levodopa levels are at its peak concentration in the serum plasma. Diarrhea
10% of patients taking entacapone have been shown to experience diarrhea. Diarrhea may occur within 4–12 weeks of initial entacapone use but resolves after discontinuation of the drug. Use of entacapone in the presence of diarrhea can also be associated with weight loss, low potassium levels, and dehydration. In clinical studies, severe diarrhea was the most common reason for discontinuation of entacapone. Urine color
10% of people taking entacapone experience a change in urine color to orange, red, brown, or black.
COMT eliminates biologically active catechols present in catecholamines (dopamine, norepinephrine, and epinephrine) and their hydroxylated metabolites. When administered with a decarboxylase inhibitor, COMT acts as the major metabolizing enzyme for levodopa and metabolizes it to 3-methoxy-4-hydroxy-L-phenylalanine (3-OMD) in the brain and in the periphery.For the treatment of Parkinsons disease, entacapone is given as an adjunct to levodopa and an aromatic amino acid decarboxylase inhibitor, carbidopa. Entacapone inhibits COMT in the periphery (but not, or at most marginally, in the brain) and the metabolism of levodopa, thus increasing plasma levels of levodopa and causing more constant dopaminergic stimulation in order to reduce the signs and symptoms presented in the disease. Pharmacokinetics
Absorption
The time to highest blood plasma concentrations is approximately one hour. The substance undergoes extensive first-pass metabolism. Absolute oral bioavailability (F) is 35%. Distribution
The volume of distribution  (Vd) after intravenous injection is approximately 20 liters. 98% of the circulating entacapone is bound to serum albumin, which limits its distribution into tissues. Metabolism and elimination
Entacapone is primarily metabolized to its glucuronide in the liver, and 5% are converted into the Z-isomer. It has a half-life of approximately 0.3–0.7 hours, with only 0.2% being excreted unchanged in the urine. References
External links
"Entacapone". Drug Information Portal. U.S. National Library of Medicine.