Is gabapentin (Neurontin) or Lyrica (pregabalin) favored for the treatment of postherpetic neuralgia?

Gabapentin is Preferred Over Pregabalin for Postherpetic Neuralgia

Gabapentin should be used as first-line therapy for postherpetic neuralgia rather than pregabalin due to its established efficacy, better cost-effectiveness, and similar clinical outcomes.

Comparative Efficacy

Both gabapentin and pregabalin are effective for postherpetic neuralgia (PHN), but the evidence supports gabapentin as the preferred initial choice:

• Gabapentin has a Number Needed to Treat (NNT) of 4.39 1
• Pregabalin has a slightly higher NNT of 4.93 1
• Both medications have FDA approval for PHN treatment 2, 3
• Both medications work through similar mechanisms by binding to voltage-dependent calcium channels

Dosing Considerations

Gabapentin

• Starting dose: 300 mg on day 1,600 mg on day 2,900 mg on day 3 2
• Target dose: 1800-2400 mg/day in divided doses 1
• Research suggests 600 mg/day can be a safe and effective starting dose for PHN patients 4
• Once-daily gastroretentive formulations are available for improved adherence 5, 6

Pregabalin

• Typical dosing: 150-600 mg/day 1
• Requires less frequent dosing (twice daily vs. three times daily for immediate-release gabapentin)
• May have more predictable absorption than gabapentin

Clinical Decision Factors

Factors favoring gabapentin as first-line therapy:

1. Cost-effectiveness: Gabapentin is generally less expensive as a generic medication
2. Established efficacy: Longer history of use with substantial evidence supporting its efficacy 7, 8
3. Flexible dosing options: Available in immediate-release and extended-release formulations
4. Similar side effect profile: Both medications have comparable adverse effects

Side Effects and Tolerability

Both medications share similar side effect profiles:

• Common adverse effects include dizziness, somnolence, and peripheral edema
• Gabapentin TID formulation has shown high incidence of dizziness (23.9%) and somnolence (27.4%) 6
• Once-daily formulations of gabapentin may reduce these side effects 6
• Both medications require dose adjustments in patients with renal impairment

Treatment Algorithm

1. First-line: Start with gabapentin

   • Begin at 300 mg on day 1,600 mg on day 2,900 mg on day 3
   • Titrate to 1800-2400 mg/day in divided doses
   • Allow 4-6 weeks for adequate trial

2. If inadequate response or intolerable side effects:

   • Switch to pregabalin 150-600 mg/day 9
   • Consider once-daily gabapentin formulation if adherence is an issue

3. If still inadequate response after 12 weeks:

   • Consider adding or switching to tricyclic antidepressants (NNT = 2.64) 1
   • Consider interventional options like pulsed radiofrequency 1

Special Considerations

• Elderly patients: Start at lower doses and titrate more slowly due to increased risk of adverse effects
• Renal impairment: Both medications require dose adjustment based on creatinine clearance
• Patients with HIV: May experience more severe and longer-lasting PHN symptoms 9

Pitfalls to Avoid

• Inadequate dosing: Ensure proper titration to therapeutic doses
• Premature discontinuation: Allow adequate trial period (4-6 weeks) before declaring treatment failure 1
• Abrupt discontinuation: Both medications should be tapered gradually to avoid withdrawal symptoms
• Overlooking comorbidities: Consider interactions with other medications and impact of comorbid conditions

In conclusion, while both gabapentin and pregabalin are effective for PHN, gabapentin should be initiated first due to its established efficacy, favorable cost profile, and similar clinical outcomes compared to pregabalin.