CARBATROL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for CARBATROL (CARBATROL).
Stabilizes neuronal membranes by blocking voltage-gated sodium channels, inhibiting repetitive firing of action potentials. Also enhances GABAergic activity.
| Metabolism | Hepatic via CYP3A4 to pharmacologically active carbamazepine-10,11-epoxide; induces CYP3A4 and other enzymes (autoinduction). |
| Excretion | Renal: 70% as metabolites (including carbamazepine-10,11-epoxide) and 2-3% as unchanged drug; biliary/fecal: 30%. |
| Half-life | Terminal elimination half-life 25-65 hours initially, then 12-17 hours after autoinduction; clinical context: requires dose adjustment after 3-5 weeks. |
| Protein binding | 75-90% bound, primarily to albumin and alpha1-acid glycoprotein. |
| Volume of Distribution | 0.8-1.4 L/kg; clinical meaning: significant tissue distribution, crosses blood-brain barrier. |
| Bioavailability | ER formulation: ~85-90% relative to immediate-release. |
| Onset of Action | Extended-release (ER): 4-12 hours for seizure control. |
| Duration of Action | Approximately 12-24 hours with ER formulation; clinical notes: allows twice-daily dosing. |
| Molecular Weight | 236.27 |
Initial dose 200 mg orally twice daily, increase by 200 mg/day at weekly intervals; maintenance 800-1200 mg/day in 2 divided doses extended-release capsules.
| Dosage form | CAPSULE, EXTENDED RELEASE |
| Renal impairment | No specific dose adjustment; monitor levels and adjust based on response and toxicity. CrCl < 10 mL/min: reduce dose by 25%. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh C). Child-Pugh A and B: start at 50% of normal dose, titrate slowly with monitoring. |
| Pediatric use | For children >6 years: initial 10-20 mg/kg/day orally in 2 divided doses, increase weekly by up to 10 mg/kg/day; maintenance 20-30 mg/kg/day. Maximum 1000 mg/day under 12 years, 1200 mg/day over 12 years. |
| Geriatric use | Start at 100 mg orally twice daily, increase slowly; monitor for hyponatremia, sedation, and fall risk. |
| 1st trimester | Associated with increased risk of neural tube defects and other major malformations. Use only if benefits outweigh risks. |
| 2nd trimester | May cause fetal anticonvulsant syndrome, including developmental delay. Monitor fetal growth and consider dose adjustment. |
| 3rd trimester | Risk of neonatal hemorrhage due to vitamin K deficiency; administer vitamin K to mother and neonate. Also risk of neonatal sedation and withdrawal. |
Clinical note
Comprehensive clinical and safety monograph for CARBATROL (CARBATROL).
| Placental transfer | Crosses placenta readily; cord blood concentrations are 50-100% of maternal serum levels. |
| Breastfeeding | Carbamazepine is excreted into breast milk at low levels. Most studies report no adverse effects in infants, but monitor for drowsiness, poor feeding, and rash. Theoretical risk of kernicterus in jaundiced neonates. |
■ FDA Black Box Warning
Aplastic anemia and agranulocytosis; obtain baseline hematologic testing before therapy and monitor periodically.
| Serious Effects |
History of bone marrow suppressionHypersensitivity to carbamazepine or tricyclic antidepressantsConcomitant use of monoamine oxidase inhibitors (MAOIs)Acute intermittent porphyria
| Precautions | Hypersensitivity reactions (including Stevens-Johnson syndrome/toxic epidermal necrolysis with HLA-B*1502 allele in Asian patients); hyponatremia; hepatic dysfunction; cardiac conduction abnormalities; withdrawal seizures; bone marrow suppression. |
| Food/Dietary | Grapefruit and grapefruit juice may increase carbamazepine levels; avoid concurrent consumption. High-fat meals may slightly increase absorption but not to a clinically significant degree. Alcohol should be avoided due to additive CNS depression. There are no other specific dietary restrictions. |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | FDA Pregnancy Category D. First trimester: major congenital malformations (neural tube defects, craniofacial defects, cardiovascular anomalies) with relative risk 2-3; neural tube defect risk 1-2% (10-fold increase). Second/third trimesters: fetal anticonvulsant syndrome (developmental delay, dysmorphic features), neonatal hemorrhage due to vitamin K deficiency, withdrawal symptoms (hyperirritability, poor feeding). |
| Fetal Monitoring | Preconception: folate supplementation (4 mg/day). First trimester: high-resolution ultrasound, maternal serum alpha-fetoprotein screening, amniocentesis for structural anomalies. Throughout pregnancy: serial growth scans, fetal echocardiography at 20-22 weeks, monitoring of liver function, CBC, and carbamazepine levels (target total 4-12 mcg/mL). Neonatal: evaluate for hemorrhagic disease (administer vitamin K immediately), withdrawal symptoms, and dysmorphic features. |
| Fertility Effects | May reduce efficacy of oral contraceptives due to enzyme induction; increased risk of contraceptive failure. No direct evidence of impaired fertility in women; men may have reduced sperm motility and count. |
| Clinical Pearls | Carbatrol (extended-release carbamazepine) should be dosed twice daily, not three times daily, due to its extended-release formulation. Therapeutic drug monitoring of carbamazepine levels (target 4-12 mcg/mL) is essential, especially during titration and with co-administration of enzyme inducers or inhibitors. Strictly avoid concurrent use with MAOIs due to risk of hypertensive crisis. Carbamazepine induces its own metabolism (autoinduction), requiring dose adjustments over first 3-4 weeks. Monitor for hyponatremia, especially in elderly, and for Stevens-Johnson syndrome, particularly in HLA-B*1502 positive patients of Asian ancestry. |
| Patient Advice | Take Carbatrol exactly as prescribed, usually twice daily with or without food. · Do not crush, chew, or break the capsules; swallow them whole. · Report any rash, fever, mouth ulcers, or blistering immediately; these could be signs of a serious allergic reaction. · Avoid alcohol as it may increase side effects like dizziness and drowsiness. · Do not drive or operate heavy machinery until you know how Carbatrol affects you. · Inform your doctor of all other medications, including birth control pills, as Carbatrol can reduce their effectiveness. · Regular blood tests are required to monitor drug levels and check for side effects like low sodium or blood cell count. · Do not stop taking Carbatrol suddenly; withdrawal can trigger seizures. |