• Acetic acid derivative, structural analogue to GABA
  • Tablets – 600/800 mg
  • Capsules 100/300/400 mg



  • Post-herpetic neuralgia
  • Post diabetic neuropathy
  • Partial seizures with or without secondary generalisation
  • Neuropathic pain

Mechanism of action

  • Structurally related to GABA but does not interact with GABA receptors.
  • Binds to alpha-2-delta subunit of voltage-gated calcium channels.
  • May also:
    • Partially reduce response to the glutamate agonist NMDA
    • Reduce the release of monoamine neurotransmitters in vitro
    • Stimulate glutamate decarboxylate (converts glutamate to GABA)
    • Increase the synaptic release of GABA


  • PO – titration scheme or alternatively an initial dose of 300 mg TDS
  • Long-term epilepsy – 900-3600 mg/day
  • Neuropathic pain – up to 3600 mg/day
  • Discontinuation should be gradually performed over a minimum of 1 week


  • Peak plasma 3hrs

DoA (duration)

  • t1/2b 5-7hrs



  • Analgesic
  • Anticonvulsant


  • Dizziness, ataxia, nystagmus, somnolence, tremor, diplopia, nausea and vomiting >5%
  • Leucopenia, erectile dysfunction and weight gain have all been reported
  • Steven-Johnson Syndrome
  • Drug reaction with eosinophilia and systemic symptoms (DRESS)



  • Well absorbed orally
  • LAT1 transporter via intestine (saturable)
  • 60% oral bioavailability
  • Peak plasma levels of the drug occur within 2-3 hours of administration


  • Minimally bound to plasma proteins (<3%)
  • Vd 0.85L/kg
  • In patients with epilepsy, gabapentin concentrations approximately 20% of corresponding plasma concentrations (ie crosses BBB w 20% levels in CSF)


  • Gabapentin not metabolised in man and does not induce hepatic enzymes


  • Excreted unchanged by renal function (will require dose reduction in renal failure)
  • Elimination half-life is 5-7 hours

Special points

  • Gabapentin enhances analgesic effect of co-administered morphine
  • Removed by haemodialysis. Bioavailability of the drug decreases with increasing dose which may minimise toxicity resulting from overdose.
  • Co-administration of drug with antacids containing aluminium and magnesium may reduce bioavailability by up to 24%.  Suicidal idealtion

Author: Michael Wu