Adults

For neuropathic pain: Initial 300 mg on day 1, 300 mg twice daily on day 2, 300 mg three times daily on day 3. Maintenance: 900-1800 mg/day in 3 divided doses. For partial seizures: Initial 300 mg three times daily, adjusted up to 1800-2400 mg/day.

Elderly

Dosage adjustments may be necessary due to age-related decrease in renal function. Start with a lower dose.

Renal_impairment

Dosage reduction is required based on creatinine clearance. For CrCl 30-59 mL/min, 200-700 mg twice daily. For CrCl 15-29 mL/min, 200-700 mg once daily.

Onset

Variable, therapeutic effects for neuropathic pain may take several days to weeks to manifest.

Excretion

Excreted unchanged in the urine. Renal elimination is the primary route.

Half life

Approximately 5 to 7 hours in healthy adults, prolonged in renal impairment.

Absorption

Oral bioavailability is dose-dependent and saturable, approximately 60% at 300 mg. Peak plasma concentrations are reached in 2-3 hours.

Metabolism

Not significantly metabolized in humans. It does not induce hepatic enzymes.

Opioids (e.g., Morphine)

May increase gabapentin concentrations and enhance central nervous system (CNS) depression, leading to increased sedation, respiratory depression, and coma. Use with caution.

Antacids (containing aluminum and magnesium)

May decrease gabapentin absorption. Administer gabapentin at least 2 hours after antacid administration.