Adults

Dosage should be individualized and gradually titrated. For neuropathic pain (e.g., postherpetic neuralgia), initial dose is often 300 mg once daily on Day 1, then 300 mg twice daily on Day 2, then 300 mg three times daily on Day 3, up to a maximum of 1800-3600 mg/day in divided doses. For partial seizures, initial doses are typically 300 mg three times daily, adjusted based on response and tolerability.

Elderly

Dosage in elderly patients should be adjusted based on renal function, similar to patients with renal impairment.

Renal_impairment

For patients with creatinine clearance <60 mL/min, dosage must be reduced significantly. Patients on hemodialysis require a supplemental dose after each dialysis session.

Onset

Onset of pain relief for neuropathic pain can be gradual, often taking several weeks to achieve optimal effect. For seizures, it acts relatively quickly, but titration is usually needed.

Excretion

Excreted primarily unchanged in the urine. Renal elimination is the sole route of excretion.

Half life

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

Absorption

Readily absorbed after oral administration via a saturable L-amino acid transport system. Bioavailability is dose-dependent, decreasing with increasing dose. Peak plasma concentrations are reached within 2-3 hours.

Metabolism

Not significantly metabolized in humans. It does not induce or inhibit hepatic enzyme systems.

Opioid analgesics (e.g., morphine)

May increase gabapentin concentrations, leading to increased CNS depression. Monitor for sedation and respiratory depression.

Antacids containing aluminum and magnesium

May decrease gabapentin bioavailability; separate administration by at least 2 hours.

Other CNS depressants (e.g., alcohol, benzodiazepines)

Increased risk of additive CNS depressant effects such as sedation, dizziness, and respiratory depression.