What is the recommended dosage and treatment regimen for Gabapentin (Neurontin) in patients with epilepsy and neuropathic pain?

Gabapentin Dosing Regimen for Epilepsy and Neuropathic Pain

For patients with epilepsy, gabapentin should be initiated at 300 mg three times daily with titration up to 1800-3600 mg/day in divided doses, while neuropathic pain treatment should start at 100-300 mg at bedtime with gradual titration to 1800-3600 mg/day in three divided doses. 1, 2

Dosing for Epilepsy

Adults and Adolescents (≥12 years)

• Starting dose: 300 mg three times daily
• Maintenance dose: 300-600 mg three times daily (900-1800 mg/day)
• Maximum dose: 2400-3600 mg/day in three divided doses
• Maximum time between doses should not exceed 12 hours 1

Pediatric Patients (3-11 years)

• Starting dose: 10-15 mg/kg/day in three divided doses
• Maintenance dose:
  • Ages 3-4 years: 40 mg/kg/day in three divided doses
  • Ages 5-11 years: 25-35 mg/kg/day in three divided doses
• Maximum dose: Up to 50 mg/kg/day has been well-tolerated 1

Dosing for Neuropathic Pain

Initial Titration Schedule

• Day 1: 100-300 mg at bedtime or 100-300 mg three times daily
• Titration: Increase by 100-300 mg every 1-7 days as tolerated 2
• Target dose: 1800-3600 mg/day in three divided doses 2, 3

Postherpetic Neuralgia Specific Titration

• Day 1: Single 300 mg dose
• Day 2: 600 mg/day (300 mg twice daily)
• Day 3: 900 mg/day (300 mg three times daily)
• Further titration as needed up to 1800 mg/day 1

Efficacy Considerations

• For neuropathic pain, approximately 38% of patients achieve substantial pain relief (≥50% reduction) compared to 21% with placebo 4
• For postherpetic neuralgia, efficacy was demonstrated over a range of 1800-3600 mg/day, with no additional benefit demonstrated above 1800 mg/day 1
• An adequate trial requires 3-8 weeks for titration plus 2 weeks at maximum dose 2
• Some patients may require up to 2 months for an adequate therapeutic assessment 2, 5

Dosage Adjustment in Special Populations

Renal Impairment

Dosage adjustment based on creatinine clearance:

• ≥60 mL/min: 900-3600 mg/day (300-1200 mg TID)

• 30-59 mL/min: 400-1400 mg/day (200-700 mg BID)

• 15-29 mL/min: 200-700 mg/day (200-700 mg QD)

• ≤15 mL/min: 100-300 mg/day (100-300 mg QD) 1, 3

Elderly Patients

• Start with lower doses and titrate more slowly
• Adjust dose based on creatinine clearance values
• Monitor closely for side effects, particularly cognitive impairment 1, 3

Common Adverse Effects

• Dizziness (19% of patients)
• Somnolence (14%)
• Peripheral edema (7%)
• Gait disturbance (14%) 4
• Adverse effects are typically mild to moderate and usually subside within approximately 10 days from treatment initiation 6

Administration Guidelines

• Can be administered with or without food
• If using scored tablets (600 mg or 800 mg), unused half-tablets should be taken as the next dose
• Half-tablets not used within 28 days should be discarded
• If discontinuing gabapentin, taper gradually over at least 1 week to minimize withdrawal symptoms 1

Important Clinical Considerations

• Gabapentin has nonlinear pharmacokinetics due to saturable absorption, requiring careful titration 2
• For epilepsy, gabapentin is typically used as adjunctive therapy when partial seizures are inadequately controlled by other antiepileptics 7
• For neuropathic pain, tricyclic antidepressants are often considered first-line, with gabapentin as an alternative 7, 3
• Adverse event withdrawals are more common with gabapentin (11%) than with placebo (8.2%) 4
• Serious adverse events are not significantly more common with gabapentin than with placebo 4

By following these dosing guidelines and monitoring for adverse effects, gabapentin can provide effective treatment for both epilepsy and neuropathic pain conditions.