Gabapentin is a gamma-aminobutyric acid (GABA) analogue anticonvulsant and neuropathic pain agent. It is structurally related to the neurotransmitter GABA but does not act on GABA receptors. It is widely used for neuropathic pain and as an adjunctive therapy for partial seizures. In India, it is a first-line agent for diabetic neuropathy and post-herpetic neuralgia.
Adult: Neuropathic Pain: Initiate at 300 mg once on Day 1, 300 mg twice daily on Day 2, 300 mg thrice daily on Day 3. Titrate as needed up to 1800-3600 mg/day in 3 divided doses. Epilepsy: 900-1800 mg/day in 3 divided doses, titrated over 3 days. Maximum efficacy dose often 1800 mg/day.
Note: Administer with or without food. If a dose is missed, take as soon as remembered unless it is almost time for the next dose. Do NOT double the dose. The capsule should be swallowed whole with a glass of water. For patients on hemodialysis, dose should be scheduled post-dialysis.
The exact mechanism is not fully elucidated. It does not interact with GABA-A or GABA-B receptors, nor does it inhibit GABA uptake or degradation. Its primary action is believed to be binding to the α2δ-1 subunit of voltage-gated calcium channels (specifically N-type and P/Q-type) in the central nervous system. This binding modulates channel function, reducing the influx of calcium into nerve terminals.
Pregnancy: Pregnancy Category C (US FDA). Data in humans is limited. Animal studies showed teratogenicity. Use only if potential benefit justifies potential risk to the fetus. In women with epilepsy, monotherapy is preferred; gabapentin is not a first-line antiepileptic in pregnancy. Indian guidelines recommend thorough risk-benefit analysis.
Driving: May impair alertness, motor coordination, and reaction time. Patients should be cautioned not to drive or operate heavy machinery until they know how the drug affects them, especially during dose titration.
| Opioids (e.g., Morphine, Codeine) | Increased risk of severe sedation, respiratory depression, and death. | Major |
| Antacids (Aluminium/Magnesium hydroxide) | Reduces gabapentin bioavailability by up to 20%. Administer gabapentin at least 2 hours after antacid. | Moderate |
| Alcohol and CNS Depressants | Additive CNS depression (somnolence, dizziness). | Major |
| Other Antiepileptics (e.g., Phenytoin, Carbamazepine) | No significant PK interaction, but additive CNS side effects. | Moderate |
| Cimetidine | Slightly decreases renal excretion of gabapentin, increasing AUC by ~14%. Usually not clinically significant. | Minor |