Treatment of Post-Herpetic Neuralgia
Start with gabapentin as first-line oral therapy, titrating from 300 mg on day 1 to 900 mg on day 3, then up to 1800-3600 mg/day in three divided doses, or use topical lidocaine 5% patches for localized pain, particularly in elderly patients. 1, 2, 3
First-Line Treatment Algorithm
Topical Therapy (Preferred for Elderly or Localized Pain)
- Lidocaine 5% patches provide excellent efficacy (NNT = 2) with minimal systemic absorption, making them ideal for elderly patients or those with comorbidities. 1, 2
- Apply patches for 12-24 hours directly on affected areas, delivering medication gradually over hours. 1
- This approach avoids systemic side effects like somnolence and dizziness that are particularly problematic in older adults. 2
Oral Gabapentin (First-Line Systemic Therapy)
- The American College of Physicians recommends gabapentin as first-line oral pharmacological treatment, with FDA-approved dosing starting at 300 mg on day 1,600 mg on day 2 (300 mg twice daily), and 900 mg on day 3 (300 mg three times daily). 1, 3
- Titrate up to 1800-3600 mg/day in three divided doses as needed for pain relief. 1, 3
- Efficacy is demonstrated across the 1800-3600 mg/day range, but no additional benefit is shown above 1800 mg/day. 1, 3
- Maximum time between doses should not exceed 12 hours. 3
- Pain reduction can be seen as early as Week 1 and is maintained throughout treatment. 3, 4
Tricyclic Antidepressants (Alternative First-Line)
- Nortriptyline has excellent efficacy (NNT = 2.64) and is preferred over amitriptyline due to better tolerability with equivalent analgesic benefit. 1, 2
- Start at 10-25 mg at bedtime and increase every 3-7 days to a final dose of 25-100 mg at bedtime. 1
- Taking at bedtime minimizes daytime sedation effects. 1
Second-Line Treatments (If Inadequate Response to First-Line)
Pregabalin
- Consider pregabalin if gabapentin provides inadequate response, with an NNT of 4.93. 1
- Effective dose typically ranges from 150-600 mg/day in two divided doses. 1, 5
- Pain reduction can occur as early as Week 1 and persists throughout treatment. 5
High-Concentration Capsaicin
- Capsaicin 8% patch can provide pain relief for at least 12 weeks. 1, 2
- Apply 4% lidocaine for 60 minutes before capsaicin application to minimize erythema and burning pain. 1, 2
Tramadol
- Shows efficacy with an NNT of 4.76 as a second-line option. 1
Third-Line Treatments (When Single Agents Fail)
Combination Therapy
- Combining morphine with gabapentin may be more effective when single agents provide inadequate relief, allowing for lower doses of each medication while providing additive effects. 1, 2
Opioids (Use with Caution)
- Oxycodone, extended-release morphine, and methadone show efficacy (NNT = 2.67) but should not be used as first-line agents. 1, 2
- Risks include pronociception, cognitive impairment, respiratory depression, endocrine/immunological changes, and potential for misuse and addiction. 1, 2
Special Population Considerations
Elderly Patients
- Start gabapentin at 100-200 mg/day in elderly patients with gradual titration. 2
- Topical lidocaine patches are particularly valuable due to minimal systemic effects. 2
- Always adjust dose based on renal function to prevent toxicity. 2
- Monitor closely for neurological side effects (somnolence, dizziness, confusion) that are particularly problematic in older adults. 2
Renal Impairment
- For creatinine clearance 30-60 mL/min: reduce gabapentin to 200-700 mg/day in divided doses. 3
- For creatinine clearance 15-30 mL/min: reduce to 200-700 mg once daily. 3
- For creatinine clearance <15 mL/min: reduce to 100-300 mg once daily. 3
- Patients on hemodialysis require supplemental post-dialysis dosing of 125-350 mg after each 4-hour session. 3
Common Pitfalls and Caveats
What NOT to Use
- Lamotrigine is not recommended for PHN due to lack of convincing evidence of efficacy and risk of lamotrigine-associated rash. 1, 2
Monitoring Requirements
- Monitor for gabapentin side effects including somnolence, dizziness, ataxia, peripheral edema, and infection. 1, 4
- These side effects are common but usually tolerable. 4
- Elderly patients are particularly susceptible to mental clouding and falls risk. 2
Dosing Errors to Avoid
- Do not underdose gabapentin—400 mg/day is far below the effective range for neuropathic pain control. 6
- Do not exceed 12 hours between gabapentin doses. 3
- Do not use doses above 1800 mg/day expecting additional benefit, though they are safe and well-tolerated. 1, 3
Non-Pharmacological Adjuncts
- Cognitive behavioral therapy (CBT), hypnosis, and physical/occupational therapy may be beneficial as adjunctive treatments. 1, 2