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Tolcapone
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Tolcapone
Tolcapone, sold under the brand name Tasmar, is a medication used to treat Parkinson's disease (PD). It is a selective, potent and reversible nitrocatechol-type inhibitor of the enzyme catechol-O-methyltransferase (COMT). It has demonstrated significant liver toxicity, which has led to suspension of marketing authorisations in a number of countries.
Tolcapone appears to be peripherally selective, but can still cross into the brain in significant amounts and has been found to inhibit COMT centrally as well[clarification needed]. In comparison with entacapone, another nitrocatechol COMT inhibitor, tolcapone has a longer half life (2.9 hours vs. 0.8 hours) and can better penetrate into the brain, acting both in the central nervous system and in the periphery. However, entacapone is less toxic for the liver.
Tolcapone is used in the treatment of Parkinson's disease as an adjunct to levodopa/carbidopa or levodopa/benserazide medications. Levodopa is a prodrug for dopamine, which reduces Parkinson symptoms; carbidopa and benserazide are aromatic L-amino acid decarboxylase (AADC) inhibitors.
Without administration of tolcapone, the beneficial effects of levodopa tend to wear off more quickly, resulting in motor fluctuations.
Combining tolcapone with non-selective monoamine oxidase inhibitors such as phenelzine or tranylcypromine is contraindicated. Tolcapone is also contraindicated for people with liver diseases or increased liver enzymes.
Tolcapone has demonstrated significant liver toxicity (hepatotoxicity) that limits the drug's utility. Entacapone is an alternative, largely since it has a more favorable toxicity profile.
The hepatotoxicity can be related to elevated levels of transaminases, but studies have shown that minimal risk exists for those without preexisting liver conditions when their enzyme levels were being monitored. No clear mechanism is implicated, but it has been hypothesized that it has something to do with abnormal mitochondrial respiration due to the uncoupling of oxidative phosphorylation.
Other side effects regard the increase in dopaminergic activity, including digestive symptoms. Treatment with tolcapone runs the risk of eliciting or prolonging dyskinesia; this can be counteracted by decreasing the dose of levodopa. This occurs because the administration of tolcapone results in the accumulation of the biological methyl donor S-adenosyl-L-methionine (SAM) in the striatum that induces Parkinson symptoms.
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Tolcapone
Tolcapone, sold under the brand name Tasmar, is a medication used to treat Parkinson's disease (PD). It is a selective, potent and reversible nitrocatechol-type inhibitor of the enzyme catechol-O-methyltransferase (COMT). It has demonstrated significant liver toxicity, which has led to suspension of marketing authorisations in a number of countries.
Tolcapone appears to be peripherally selective, but can still cross into the brain in significant amounts and has been found to inhibit COMT centrally as well[clarification needed]. In comparison with entacapone, another nitrocatechol COMT inhibitor, tolcapone has a longer half life (2.9 hours vs. 0.8 hours) and can better penetrate into the brain, acting both in the central nervous system and in the periphery. However, entacapone is less toxic for the liver.
Tolcapone is used in the treatment of Parkinson's disease as an adjunct to levodopa/carbidopa or levodopa/benserazide medications. Levodopa is a prodrug for dopamine, which reduces Parkinson symptoms; carbidopa and benserazide are aromatic L-amino acid decarboxylase (AADC) inhibitors.
Without administration of tolcapone, the beneficial effects of levodopa tend to wear off more quickly, resulting in motor fluctuations.
Combining tolcapone with non-selective monoamine oxidase inhibitors such as phenelzine or tranylcypromine is contraindicated. Tolcapone is also contraindicated for people with liver diseases or increased liver enzymes.
Tolcapone has demonstrated significant liver toxicity (hepatotoxicity) that limits the drug's utility. Entacapone is an alternative, largely since it has a more favorable toxicity profile.
The hepatotoxicity can be related to elevated levels of transaminases, but studies have shown that minimal risk exists for those without preexisting liver conditions when their enzyme levels were being monitored. No clear mechanism is implicated, but it has been hypothesized that it has something to do with abnormal mitochondrial respiration due to the uncoupling of oxidative phosphorylation.
Other side effects regard the increase in dopaminergic activity, including digestive symptoms. Treatment with tolcapone runs the risk of eliciting or prolonging dyskinesia; this can be counteracted by decreasing the dose of levodopa. This occurs because the administration of tolcapone results in the accumulation of the biological methyl donor S-adenosyl-L-methionine (SAM) in the striatum that induces Parkinson symptoms.
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