Tolcapone
Encyclopedia
Tolcapone is a drug
Drug
A drug, broadly speaking, is any substance that, when absorbed into the body of a living organism, alters normal bodily function. There is no single, precise definition, as there are different meanings in drug control law, government regulations, medicine, and colloquial usage.In pharmacology, a...

 that inhibits the enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 catechol-O-methyl transferase
Catechol-O-methyl transferase
Catechol-O-methyltransferase is one of several enzymes that degrade catecholamines such as dopamine, epinephrine, and norepinephrine. In humans, catechol-O-methyltransferase protein is encoded by the COMT gene...

 (COMT).

Uses

Tolcapone is used in the treatment of Parkinson's disease
Parkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...

 as an adjunct to levodopa/carbidopa medication.

Chemistry

Tolcapone is a yellow, odorless, non-hygroscopic, crystalline compound with a relative molecular mass
Molecular mass
The molecular mass of a substance is the mass of one molecule of that substance, in unified atomic mass unit u...

 of 273.25. The chemical name of tolcapone is 3,4-dihydroxy-4’-methyl-5-nitrobenzophenone. Its empirical formula is C14H11NO5.

Pharmacology

Tolcapone has the ability to cross the blood-brain barrier
Blood-brain barrier
The blood–brain barrier is a separation of circulating blood and the brain extracellular fluid in the central nervous system . It occurs along all capillaries and consists of tight junctions around the capillaries that do not exist in normal circulation. Endothelial cells restrict the diffusion...

 and thus exerts its COMT inhibitory effects in the CNS as well as in the periphery.

Tolcapone has demonstrated significant hepatotoxicity
Hepatotoxicity
Hepatotoxicity implies chemical-driven liver damage.The liver plays a central role in transforming and clearing chemicals and is susceptible to the toxicity from these agents. Certain medicinal agents, when taken in overdoses and sometimes even when introduced within therapeutic ranges, may injure...

 that limits the drug's utility. Entacapone
Entacapone
Entacapone is a drug that functions as a catechol-O-methyl transferase inhibitor. It is used in the treatment of Parkinson's disease....

, another COMT inhibitor, is an alternative selection for L-DOPA adjunct therapy in the treatment of Parkinson's disease
Parkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...

, largely since it has a more favorable toxicity profile.

Normally, administration of levodopa is compromised when COMT converts it to 3-methoxy-dopa. By preventing this effect, more of the levodopa that is administered reaches the CNS. Additionally, levodopa that is in the CNS, after being converted to dopamine, will not be degraded by COMT when tolcapone inhibits COMT activity.
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