Pharm 101: Carbamazepine

Class

Anticonvulsant
Mood stabiliser


Pharmacodynamics
  • 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

Pharmacokinetics
  • 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 (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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