Gabapentin
Class: anticonvulsant (gabapentinoid)
Indications: partial seizures, including secondarily generalised tonic-clonic seizures, initially as add-on therapy in patients who have not achieved adequate control with standard antiepileptic drugs, neuropathic pain, (NB some may be unlicensed): insomnia; pruritis; hot flushes; sweating; refractory hiccup; restless legs syndrome; spasticity; refractory cough; alcohol withdrawal
Contraindications/cautions: renal disease (reduce dose), absence seizures, encephalopathy; psychotic illness
Adverse reactions: common: easy bruising (purpura), increased blood pressure, drowsiness, dizziness, ataxia, blurred vision; dry mouth; less common: fatigue, headache, anxiety, GI effects(nausea, vomiting, diarrhoea, constipation), sexual dysfunction, oedema, twitching, tremor, confusion, suicidal thoughts
Metabolism/clearance: not metabolised, mainly excreted unchanged by the kidneys (fraction excreted unchanged by the kidney = 0.8) adjust dose in renal dysfunction
Interactions:
- decreased clinical effect/toxicity of gabapentin with antacids containing aluminium or magnesium e.g. Mylanta PTM due to decreased absorption of gabapentin
- additive CNS depression with other CNS depressants e.g. benzodiazepines (e.g. lorazepam), phenothiazines (e.g. chlorpromazine), tricyclic antidepressants (e.g. amitriptyline), opioids, alcohol
| Dosing: | ||
|---|---|---|
| oral: | epilepsy | 900 to 1,800 mg/day in 3 divided doses max 3,600 mg |
| peripheral neuropathic pain | 900 to 3,600 mg/day in 3 divided doses — commence low dose and increase slowly — 300 mg once daily and increase by 300 mg daily until 3 times daily – increase every 2 to 3 days up to maximum 3600 mg daily | |
| Pruritis in ESRD | after dialysis; increase gradually to 300 mg daily if necessary | |
| Intractable hiccup | 100 to 300 mg daily increasing every 2 to 3 days as tolerated & according to response — max 1200 mg daiy in divided doses (NZF) | |
| subcut: | not available | |
| rectal: | not available | |
Syringe driver: not available
Mechanism of action: Gabapentin is thought to bind to voltage-gated calcium channels, reducing calcium influx into presynaptic terminals and possibly decreasing the release of excitatory neurotransmitters associated with neuropathic pain and seizure propagation