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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for CARBATROL (CARBATROL).
| Breastfeeding | Excreted into breast milk; infant serum levels 10-60% of maternal trough; M/P ratio approximately 0.4-0.6. American Academy of Pediatrics considers compatible with breastfeeding but monitor for drowsiness, poor suckling. |
| 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). |
■ FDA Black Box Warning
Aplastic anemia and agranulocytosis; obtain baseline hematologic testing before therapy and monitor periodically.
| Serious Effects |
History of bone marrow depression; known hypersensitivity to carbamazepine or tricyclic antidepressants; concomitant MAO inhibitor use within 14 days; use with nefazodone; HLA-B*1502 positive patients (unless benefits outweigh risks).
| 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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| 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. |