Adults

Initial titration: 25 mg once daily at bedtime, increasing gradually as tolerated. Common starting doses are 100-300 mg daily, titrated up to 900-3600 mg/day in divided doses depending on indication. For postherpetic neuralgia: Start with 300 mg on day 1, 300 mg twice daily on day 2, and 300 mg three times daily on day 3. For epilepsy: Start with 300 mg three times a day. Max dose: 3600 mg/day.

Elderly

Dosage should be individualized based on renal function and careful titration due to increased risk of side effects.

Renal_impairment

Dosage adjustment is necessary. For CrCl 30-59 mL/min: 200-700 mg twice daily. For CrCl 15-29 mL/min: 200-700 mg once daily. For CrCl <15 mL/min: 100-300 mg once daily. Hemodialysis patients require a supplementary dose.

Onset

Therapeutic effects may take several days to weeks to become fully apparent, especially for chronic pain or seizure control.

Excretion

Excreted unchanged by the kidneys, primarily through glomerular filtration and active tubular secretion.

Half life

Approximately 5 to 7 hours in adults with normal renal function.

Absorption

Oral absorption is dose-dependent and saturable, with bioavailability decreasing with increasing doses. Peak plasma concentrations are reached within 2-3 hours.

Metabolism

Gabapentin is not significantly metabolized in humans. It does not induce or inhibit hepatic drug-metabolizing enzymes.

Cimetidine

May slightly reduce renal excretion of gabapentin; clinical significance is usually minimal.

Hydrocodone

Concurrent use may increase gabapentin exposure.

Antacids (e.g., Maalox)

Can reduce gabapentin bioavailability by about 20%. Take gabapentin at least 2 hours after antacid administration.

Opioids (e.g., Morphine)

Can increase gabapentin concentrations. Concomitant use should be carefully monitored, and gabapentin dose may need reduction.