Gabapentin Dosage for Postherpetic Neuralgia
For postherpetic neuralgia, gabapentin should be initiated at 300 mg on day 1, increased to 600 mg/day (300 mg twice daily) on day 2, and to 900 mg/day (300 mg three times daily) on day 3, with subsequent titration to an effective dose of 1800 mg/day. 1
Initial Dosing and Titration
The FDA-approved dosing regimen for gabapentin in postherpetic neuralgia follows a specific titration schedule:
- Day 1: 300 mg as a single dose
- Day 2: 600 mg/day (300 mg twice daily)
- Day 3: 900 mg/day (300 mg three times daily)
- Subsequently: Titrate up as needed for pain relief 1
The target dose is 1800 mg/day (600 mg three times daily), which has demonstrated efficacy in clinical studies. While doses up to 3600 mg/day have been studied, the additional benefit of using doses greater than 1800 mg/day was not clearly demonstrated in clinical trials. 1
Efficacy Evidence
Gabapentin has shown significant efficacy for postherpetic neuralgia with a number needed to treat (NNT) of 4.39, indicating good analgesic efficacy. 2 In postherpetic neuralgia specifically:
- 32% of patients achieve substantial pain relief (at least 50% reduction) with gabapentin at doses of 1200 mg/day or greater compared to 17% with placebo (NNT 6.7) 3
- 46% achieve moderate pain relief (at least 30% reduction) compared to 25% with placebo (NNT 4.8) 3
Dosage Adjustment in Special Populations
Renal Impairment
Dosage adjustment is required in patients with compromised renal function:
| Creatinine Clearance (mL/min) | Total Daily Dose Range (mg/day) | Dose Regimen |
|---|---|---|
| ≥60 | 900-3600 | 300-1200 mg TID |
| 30-59 | 400-1400 | 200-700 mg BID |
| 15-29 | 200-700 | 200-700 mg QD |
| <15 | 100-300 | 100-300 mg QD |
Patients on hemodialysis should receive a supplemental dose after each 4-hour hemodialysis session. 1
Elderly Patients
Elderly patients are more likely to have decreased renal function, so dose should be adjusted based on creatinine clearance values. Start at the lower end of the dosing range and titrate more slowly. 1
Adverse Effects and Monitoring
Common adverse effects include:
- Dizziness (19% of patients)
- Somnolence (14%)
- Peripheral edema (7%)
- Gait disturbance (14%) 3
Adverse event withdrawals are more common with gabapentin (11%) than with placebo (8.2%), with a number needed to harm (NNH) of 30. 3
Alternative Formulations
While the standard immediate-release gabapentin formulation requires three-times-daily dosing, once-daily gastroretentive formulations have been developed that may improve adherence and potentially reduce some adverse effects like dizziness and somnolence. 4 However, the FDA-approved standard formulation remains the most well-studied option with established efficacy.
Alternative Treatment Options
If gabapentin is ineffective or poorly tolerated, consider pregabalin as an alternative. Pregabalin has a more straightforward dosing regimen starting at 150 mg/day in 2-3 divided doses, which can be titrated to 300 mg/day after 1-2 weeks. 2
Practical Recommendations
- Start with the FDA-approved titration schedule (300 mg → 600 mg → 900 mg over 3 days)
- Continue titration to 1800 mg/day (600 mg three times daily) as tolerated
- Allow 2-8 weeks for adequate titration plus 2 weeks at maximum dose to assess efficacy 2
- If inadequate response at 1800 mg/day, doses up to 3600 mg/day may be considered, though additional benefit is uncertain
- Monitor for common adverse effects, particularly in elderly patients
- Adjust dose based on renal function in appropriate patients
By following this evidence-based dosing regimen, patients with postherpetic neuralgia can achieve optimal pain relief while minimizing adverse effects.