TOLCAPONE- tolcapone tablet, film coated
Before prescribing Tolcapone tablets, the physician should be thoroughly familiar with the details of this prescribing information.
TOLCAPONE TABLETS SHOULD NOT BE USED BY PATIENTS UNTIL THERE HAS BEEN A COMPLETE DISCUSSION OF THE RISKS AND THE PATIENT HAS PROVIDED WRITTEN ACKNOWLEDGEMENT THAT THE RISKS HAVE BEEN EXPLAINED (SEE PATIENT ACKNOWLEDGEMENT OF RISKS SECTION).
Because of the risk of potentially fatal, acute fulminant liver failure, Tolcapone tablets should ordinarily be used in patients with Parkinson’s disease on l-dopa/carbidopa who are experiencing symptom fluctuations and are not responding satisfactorily to or are not appropriate candidates for other adjunctive therapies (see INDICATIONS and DOSAGE AND ADMINISTRATION sections).
Because of the risk of liver injury and because Tolcapone tablets, when it is effective, provides an observable symptomatic benefit, the patient who fails to show substantial clinical benefit within 3 weeks of initiation of treatment, should be withdrawn from Tolcapone tablets.
Tolcapone tablets therapy should not be initiated if the patient exhibits clinical evidence of liver disease or two SGPT/ALT or SGOT/AST values greater than the upper limit of normal. Patients with severe dyskinesia or dystonia should be treated with caution (see PRECAUTIONS: Rhabdomyolysis).
PATIENTS WHO DEVELOP EVIDENCE OF HEPATOCELLULAR INJURY WHILE ON TOLCAPONE TABLETS AND ARE WITHDRAWN FROM THE DRUG FOR ANY REASON MAY BE AT INCREASED RISK FOR LIVER INJURY IF TOLCAPONE TABLETS IS REINTRODUCED. ACCORDINGLY, SUCH PATIENTS SHOULD NOT ORDINARILY BE CONSIDERED FOR RETREATMENT.
Cases of severe hepatocellular injury, including fulminant liver failure resulting in death, have been reported in postmarketing use. As of May 2005, three cases of fatal fulminant hepatic failure have been reported from more than 40,000 patient years of worldwide use. This incidence may be 10- to 100-fold higher than the background incidence in the general population. Underreporting of cases may lead to significant underestimation of the increased risk associated with the use of Tolcapone tablets. All three cases were reported within the first six months of initiation of treatment with Tolcapone tablets. Analysis of the laboratory monitoring data in over 3,400 Tolcapone tablets-treated patients participating in clinical trials indicated that increases in SGPT/ALT or SGOT/AST, when present, generally occurred within the first 6 months of treatment with Tolcapone tablets.
A prescriber who elects to use Tolcapone tablets in face of the increased risk of liver injury is strongly advised to monitor patients for evidence of emergent liver injury. Patients should be advised of the need for self-monitoring for both the classical signs of liver disease (e.g., clay colored stools, jaundice) and the nonspecific ones (e.g., fatigue, loss of appetite, lethargy).
Although a program of periodic laboratory monitoring for evidence of hepatocellular injury is recommended, it is not clear that periodic monitoring of liver enzymes will prevent the occurrence of fulminant liver failure. However, it is generally believed that early detection of drug-induced hepatic injury along with immediate withdrawal of the suspect drug enhances the likelihood for recovery. Accordingly, the following liver monitoring program is recommended.
Before starting treatment with Tolcapone tablets, the physician should conduct appropriate tests to exclude the presence of liver disease. In patients determined to be appropriate candidates for treatment with Tolcapone tablets, serum glutamic-pyruvic transaminase (SGPT/ALT) and serum glutamic-oxaloacetic transaminase (SGOT/AST) levels should be determined at baseline and periodically (i.e., every 2 to 4 weeks) for the first 6 months of therapy. After the first six months, periodic monitoring is recommended at intervals deemed clinically relevant. Although more frequent monitoring increases the chances of early detection, the precise schedule for monitoring is a matter of clinical judgment. If the dose is increased to 200 mg tid (see DOSAGE AND ADMINISTRATION section), liver enzyme monitoring should take place before increasing the dose and then be conducted every 2 to 4 weeks for the following 6 months of therapy. After six months, periodic monitoring is recommended at intervals deemed clinically relevant.
Tolcapone tablets should be discontinued if SGPT/ALT or SGOT/AST levels exceed 2 times the upper limit of normal or if clinical signs and symptoms suggest the onset of hepatic dysfunction (persistent nausea, fatigue, lethargy, anorexia, jaundice, dark urine, pruritus, and right upper quadrant tenderness).
Tolcapone tablets is available as tablets containing 100 mg tolcapone.
Tolcapone, an inhibitor of catechol-O-methyltransferase (COMT), is used in the treatment of Parkinson’s disease as an adjunct to levodopa/carbidopa therapy. It is a yellow, odorless, non-hygroscopic, crystalline compound with a relative molecular mass of 273.25. The chemical name of tolcapone is 3,4-dihydroxy-4′-methyl-5-nitrobenzophenone. Its empirical formula is C14 H11 NO5 and its structural formula is:
Inactive ingredients: Core: microcrystalline cellulose, lactose monohydrate, anhydrous dibasic calcium phosphate, sodium starch glycolate, povidone, talc, magnesium stearate, and purified water. Film Coating: hypromellose, titanium dioxide, talc, ethylcellulose, triacetin, sodium lauryl sulfate, yellow iron oxide, red iron oxide, and purified water.
Mechanism of Action:
Tolcapone is a selective and reversible inhibitor of catechol-O -methyltransferase (COMT).
In mammals, COMT is distributed throughout various organs. The highest activities are 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, epinephrine) and their hydroxylated metabolites. The function of COMT is 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 metabolism to 3-methoxy-4-hydroxy-L-phenylalanine (3-OMD) in the brain and periphery.
The precise mechanism of action of tolcapone is unknown, but it is believed to be related to its ability to inhibit COMT and alter the plasma pharmacokinetics of levodopa. When tolcapone is given in conjunction with levodopa and an aromatic amino acid decarboxylase inhibitor, such as carbidopa, plasma levels of levodopa are more sustained than after administration of levodopa and an aromatic amino acid decarboxylase inhibitor alone. It is believed that these sustained plasma levels of levodopa result in more constant dopaminergic stimulation in the brain, leading to greater effects on the signs and symptoms of Parkinson’s disease in patients as well as increased levodopa adverse effects, sometimes requiring a decrease in the dose of levodopa. Tolcapone enters the CNS to a minimal extent, but has been shown to inhibit central COMT activity in animals.
COMT Activity in Erythrocytes:
Studies in healthy volunteers have shown that tolcapone reversibly inhibits human erythrocyte catechol-O-methyltransferase (COMT) activity after oral administration. The inhibition is closely related to plasma tolcapone concentrations. With a 200-mg single dose of tolcapone, maximum inhibition of erythrocyte COMT activity is on average greater than 80%. During multiple dosing with tolcapone (200 mg tid), erythrocyte COMT inhibition at trough tolcapone blood concentrations is 30% to 45%.
Effect on the Pharmacokinetics of Levodopa and its Metabolites:
When tolcapone is administered together with levodopa/carbidopa, it increases the relative bioavailability (AUC) of levodopa by approximately twofold. This is due to a decrease in levodopa clearance resulting in a prolongation of the terminal elimination half-life of levodopa (from approximately 2 hours to 3.5 hours). In general, the average peak levodopa plasma concentration (Cmax ) and the time of its occurrence (Tmax ) are unaffected. The onset of effect occurs after the first administration and is maintained during long-term treatment. Studies in healthy volunteers and Parkinson’s disease patients have confirmed that the maximal effect occurs with 100 mg to 200 mg tolcapone. Plasma levels of 3-OMD are markedly and dose-dependently decreased by tolcapone when given with levodopa/carbidopa.
Population pharmacokinetic analyses in patients with Parkinson’s disease have shown the same effects of tolcapone on levodopa plasma concentrations that occur in healthy volunteers.
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