Generic Name

Carbamazepine

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Classification

FDA Approved Indications

• Epilepsy (partial seizures, generalized seizures, trigeminal neuralgia)
• Bipolar disorder (manic episodes)

Mechanism of Action

Carbamazepine stabilizes hyperexcited nerve membranes, inhibits repetitive firing, and reduces synaptic propagation of impulses by blocking voltage-gated sodium channels.

Dosage and Administration

Adult: Initial dose typically 200 mg twice daily, titrated gradually; maintenance doses vary based on indication and response.

Pediatric: Dose is based on age and weight; usually starting around 10-20 mg/kg/day divided into 2-4 doses.

Geriatric: Start at lower doses, titrate slowly due to increased sensitivity and potential comorbidities.

Renal Impairment: Adjust doses cautiously, no specific guidelines—monitor levels and renal function.

Hepatic Impairment: Use with caution; dose adjustment may be necessary, monitor liver function.

Pharmacokinetics

Absorption: Well absorbed orally, with peak levels in 4-8 hours.

Distribution: Widely distributed; protein binding approximately 70-80%.

Metabolism: Primarily hepatic via CYP3A4; active metabolite is carbamazepine-10,11-epoxide.

Excretion: Renal excretion of parent drug and metabolites.

Half Life: Initially 25-65 hours, decreases to 12-17 hours with chronic use due to autoinduction.

Contraindications

• History of Bone Marrow Suppression, including Agranulocytosis, Aplastic Anemia.
• History of hypersensitivity to carbamazepine or similar drugs.
• History of Leucopenia or Aplastic Anemia.

Precautions

• Monitor blood counts regularly.
• Use cautiously in hepatic or renal impairment.
• Potential for hypersensitivity reactions, including Stevens-Johnson syndrome, especially in patients with HLA-B*1502 allele (particularly in Asian populations).

Adverse Reactions - Common

• Dizziness (Common)
• Drowsiness (Common)
• Unsteady gait (Common)
• Nausea (Common)
• Diplopia (Common)

Adverse Reactions - Serious

• Agranulocytosis (Rare)
• Aplastic anemia (Very rare)
• SJS/TENS (Stevens-Johnson syndrome / Toxic Epidermal Necrolysis) (Rare)
• Hepatotoxicity (Rare)
• Serious hypersensitivity reactions (Rare)

Drug-Drug Interactions

• Inhibitors or inducers of CYP3A4 (e.g., erythromycin, carbamazepine, phenytoin, warfarin)
• Drugs that affect bone marrow (e.g., chloramphenicol)

Drug-Food Interactions

• Grapefruit juice may increase levels.

Drug-Herb Interactions

N/A

Nursing Implications

Patient/Family Teaching

• Take medication as prescribed, do not stop abruptly.
• Report signs of hypersensitivity, unusual bleeding, or rash.
• Avoid alcohol and CNS depressants.
• Regular blood tests are necessary.

Special Considerations

Black Box Warnings:

• Serious dermatologic and hypersensitivity reactions, including SJS and toxic epidermal necrolysis, with increased risk in patients with HLA-B*1502 allele.
• Blood dyscrasias.
• Possible increased risk of suicidal thoughts and behaviors.

Genetic Factors: Screen for HLA-B*1502 allele in Asian patients to assess risk for SJS.

Lab Test Interference: Can cause false positives in some assays for antiepileptic drug levels and may interfere with certain laboratory tests.

Overdose Management

Signs/Symptoms: Dizziness, drowsiness, nystagmus, seizures, coma, and cardiovascular collapse.

Treatment: Supportive care, activated charcoal if within 1-2 hours of ingestion, and specific measures to maintain airway, breathing, and circulation. Hemodialysis may be considered in severe cases.

Storage and Handling

Storage: Store at room temperature away from moisture, heat, and light.

Stability: Stable for up to 2 years when stored properly.