Pharm 101: Carbamazepine


Mood stabiliser

  • Structurally similar to tricyclic antidepressants such as imipramine
  • Works by sodium channel blockade in a manner similar to phenytoin:
    • Presynaptic blockade of synaptic transmission
    • Inhibits high frequency repetitive firing of neurons
  • Also acts at adenosine receptors and as an anti-cholinergic
  • Bioavailability ~99%
  • Peak levels 6-8 hours after administration, food slows absorption
  • Volume of distribution 1L/kg
  • 70% plasma protein bound
  • Liver metabolism to active metabolites (carbamazepine epoxide), only 5% excreted unchanged
  • Half life initially 36 hours then shortens over time to 12 hours
  • CYP enzyme inducer:
    • Results in increased clearance of anticonvulsant drugs including itself, as well as phenytoin, valproate, lamotrigine, diazepam
    • Can result in breakthrough seizures
    • Increases metabolism of OCP reducing its effectiveness
    • Note valproate and phenytoin may inhibit carbamazepine elimination
Clinical uses
  • Anticonvulsant for partial and generalised tonic-clonic seizures
  • Bipolar mood disorder
  • Trigeminal neuralgia
Adverse effects
  • CNS:
    • Nystagmus, diplopia
    • Ataxia
    • Sedation occurs only at high doses
  • GI: upset, hepatic dysfunction
  • Haematological: benign leukopenia
  • Dermatological: erythematous skin rash, rarely Stevens-Johnson Syndrome
  • Metabolic: hyponatraemia
  • Overdose causes seizures and cardiac toxicity. Activated charcoal may assist in elimination of drug
Further Reading
Pharm 101 700

Pharmacology 101

Top 200 drugs

MBBS CCPU (RCE, Biliary, DVT, E-FAST, AAA) Rob is an Emergency Medicine Advanced Trainee based in Melbourne, Australia. He has special interests in medical education, ECG interpretation, and the use of diagnostic and procedural ultrasound in the undifferentiated and unwell patient.

Follow him on twitter: @rob_buttner | ECG Library |

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