Carbamazepine

Summary

Carbamazepine is a drug used to treat trigeminal neuralgia, focal seizures, and bipolar disorder. It works by blocking sodium channels in neurons, which prevents the rapid firing of action potentials. Carbamazepine is primarily used to treat trigeminal neuralgia and partial seizures, which are both thought to result from neuronal overactivation. Carbamazepine is also useful for treating manic episodes in bipolar disorder. One of the feared, but rare side effects of taking carbamazepine use is agranulocytosis, which describes a drug-induced fall in granulocyte counts, leaving patients prone to severe infections. Carbamazepine induces CYP or cytochrome 450 enzymes, so be on the lookout for drug interactions. Other side effects to look out for include SIADH and teratogenicity. Less important side effects include Steven Johnson Syndrome, diplopia, ataxia, and hepatotoxicity. 

Key Points

• Carbamazepine
  • Mechanism
    • Blocks Na+ channels
      • Inhibits rapid neuronal firing by preventing sodium (Na+) channels to recover from inactivation (prolonging refractory period)
  • Clinical Use
    • Trigeminal neuralgia (1st line)
    • Focal seizures
      • Considered a narrow-spectrum antiepileptic;  very rarely used for generalized (tonic-clonic) seizures
    • Bipolar disorder
      • Carbamazepine is especially useful for treating manic episodes
  • Adverse Effects
    • Agranulocytosis/aplastic anemia
      • Most feared but rare - stop immediately if neutrophil count drops after administration
    • Induces cytochrome P450
      • Since carbamazepine is also metabolized by CYP enzymes, this drug reduces its own levels
      • May interact with warfarin, theophylline, etc.
      • Can indirectly cause osteoporosis by increasing catabolism of vitamin D
    • SIADH
    • Teratogen
      • May cause cleft lip/palate, spina bifida and other neural tube defects
    • Steven Johnson Syndrome (SJS)
      • May cause drug-induced autoimmune skin reaction with rash and skin necrosis
    • Diplopia, ataxia, liver toxicity