USMLE Step 1







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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