Drug Groups

approved; investigational

Description

Entacapone is a selective, reversible catechol-O-methyl transferase (COMT) inhibitor for the treatment of Parkinson's disease. It is a member of the class of nitrocatechols. When administered concomittantly with levodopa and a decarboxylase inhibitor (e.g., carbidopa), increased and more sustained plasma levodopa concentrations are reached as compared to the administration of levodopa and a decarboxylase inhibitor.

Indication

Used as an adjunct to levodopa / carbidopa in the symptomatic treatment of patients with idiopathic Parkinson's Disease who experience the signs and symptoms of end-of-dose "wearing-off".

Pharmacology

Entacapone is structurally and pharmacologically related to tolcapone, but unlike tolcapone, is not associated with hepatotoxicity. Entacapone is used in the treatment of Parkinson’s disease as an adjunct to levodopa/carbidopa therapy. Entacapone is a selective and reversible inhibitor of catechol-O-methyltransferase (COMT). In mammals, COMT is distributed throughout various organs with the highest activities in the liver and kidney. COMT also occurs in the heart, lung, smooth and skeletal muscles, intestinal tract, reproductive organs, various glands, adipose tissue, skin, blood cells and neuronal tissues, especially in glial cells. COMT catalyzes the transfer of the methyl group of S-adenosyl-L-methionine to the phenolic group of substrates that contain a catechol structure. Physiological substrates of COMT include dopa, catecholamines (dopamine, norepinephrine, and epinephrine) and their hydroxylated metabolites. The function of COMT is the elimination of biologically active catechols and some other hydroxylated metabolites. COMT is responsible for the elimination of biologically active catechols and some other hydroxylated metabolites. In the presence of a decarboxylase inhibitor, COMT becomes the major metabolizing enzyme for levodopa, catalyzing the it to 3-methoxy-4-hydroxy-L-phenylalanine (3-OMD) in the brain and periphery.

Toxicity

Side effect include increase the occurrence of orthostatic hypotension, severe rhabdomyolysis, dyskinesia, hallucinations, hyperkinesia, hypokinesia, dizziness, fatigu,e gastrointestinal effects including abdominal pain constipation diarrhea nausea

Affected Organisms

Biotransformation

Metabolized via isomerization to the cis-isomer, followed by direct glucuronidation of the parent and cis-isomer.

Absorption

Entacapone is rapidly absorbed (approximately 1 hour). The absolute bioavailability following oral administration is 35%.

Half Life

0.4-0.7 hour

Protein Binding

98% (bind to serum albumin)

Elimination

Entacapone is almost completely metabolized prior to excretion, with only a very small amount (0.2% of dose) found unchanged in urine. As only about 10% of the entacapone dose is excreted in urine as parent compound and conjugated glucuronide, biliary excretion appears to be the major route of excretion of this drug.

Distribution

* 20 L

Clearance

* 850 mL/min

References

External Links