COMTAN
Clinical safety rating: caution
Comprehensive clinical and safety monograph for COMTAN (COMTAN).
Selective and reversible inhibitor of catechol-O-methyltransferase (COMT), which inhibits the metabolism of levodopa to 3-O-methyldopa, thereby increasing the plasma half-life and bioavailability of levodopa in the brain.
| Metabolism | Extensively metabolized via glucuronidation (UGT1A9 and UGT2B7) and to a minor extent via COMT itself and CYP1A2, CYP2A6, CYP2C9, CYP2E1, CYP3A4, and CYP3A5. |
| Excretion | Primarily fecal (90%) as unchanged drug; renal excretion accounts for approximately 10%, mostly as glucuronide conjugates. |
| Half-life | Terminal elimination half-life is approximately 0.4 to 0.7 hours (mean 0.7 hours) in plasma, but the pharmacodynamic half-life (COMT inhibition) is longer, about 2-4 hours, supporting thrice-daily dosing. |
| Protein binding | Primarily bound to human serum albumin, approximately 98-99% bound. |
| Volume of Distribution | Approximately 0.3 L/kg, indicating distribution primarily into extracellular fluid. |
| Bioavailability | Oral bioavailability is approximately 60% due to first-pass metabolism (glucuronidation). |
| Onset of Action | Oral: Onset of COMT inhibition occurs within 1 hour; peak plasma concentrations are reached at approximately 1 hour post-dose. |
| Duration of Action | Duration of COMT inhibition is approximately 8-12 hours with thrice-daily dosing; clinically, it extends the half-life of levodopa by about 50-100%. |
200 mg orally once daily, increased to 200 mg three times daily as tolerated, with each dose of levodopa/carbidopa; maximum 200 mg per dose.
| Dosage form | TABLET |
| Renal impairment | No dosage adjustment required for mild to moderate renal impairment (CrCl >25 mL/min). Not recommended in severe renal impairment (CrCl <25 mL/min). |
| Liver impairment | Contraindicated in patients with severe hepatic impairment (Child-Pugh class C). For moderate impairment (Child-Pugh class B), use with caution and consider dose reduction; no specific guidelines available, monitor for adverse effects. |
| Pediatric use | Safety and efficacy not established; no recommended pediatric dosing. |
| Geriatric use | No specific dose adjustment required; initiate at lower end of dosing range (200 mg once daily) and titrate slowly due to increased risk of adverse effects (e.g., dyskinesia, hallucinations). |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for COMTAN (COMTAN).
| Breastfeeding | Excreted in animal milk; unknown in human milk. Caution advised; M/P ratio not established. Consider developmental and health benefits of breastfeeding along with mother's clinical need and potential adverse effects on infant. |
| Teratogenic Risk | No adequate studies in pregnant women. Animal studies show fetal harm at high doses. Risk cannot be ruled out; use only if potential benefit justifies potential risk. First trimester: unknown risk; second and third trimesters: no specific malformation pattern reported but potential for fetal harm. |
■ FDA Black Box Warning
None
| Serious Effects |
["Hypersensitivity to entacapone or any component","Severe hepatic impairment (Child-Pugh class C)","Concurrent use of non-selective MAO inhibitors (e.g., phenelzine, tranylcypromine)"]
| Precautions | ["Risk of hepatotoxicity (elevated liver enzymes, rare cases of fulminant hepatitis)","May exacerbate levodopa-induced dyskinesias and hypotension","May cause diarrhea (sometimes severe)","May cause urine discoloration (brownish-orange)","Caution in patients with severe hepatic impairment"] |
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| Fetal Monitoring |
| Monitor liver function tests, complete blood count, and for signs of orthostatic hypotension. In pregnant women, monitor fetal growth and well-being with ultrasound as clinically indicated. |
| Fertility Effects | In animal studies, reduced fertility observed at high doses. Human data insufficient to determine effect on fertility. |