What are the treatment options and prognosis for post-herpetic neuralgia (PHN) pain after shingles?

Treatment Options for Post-Herpetic Neuralgia Pain

For post-herpetic neuralgia (PHN), first-line treatment should be gabapentin, tricyclic antidepressants, or topical lidocaine patches, with gabapentin showing excellent efficacy in randomized controlled trials. 1, 2

First-Line Treatment Options

• Gabapentin: Start with 300 mg on day 1,600 mg on day 2, and 900 mg on day 3, titrating up to 1800-3600 mg/day as needed for pain relief, with clinical studies showing efficacy across this dose range (though no additional benefit demonstrated above 1800 mg/day) 1, 2

• Tricyclic antidepressants (TCAs): Excellent efficacy with number needed to treat (NNT) of 2.64, with nortriptyline preferred over amitriptyline due to better tolerability with equivalent analgesic benefit 1, 3

• Topical lidocaine patches (5%): Provide excellent efficacy (NNT = 2) with minimal systemic absorption, making them particularly suitable for elderly patients or those with comorbidities 1

• Capsaicin: Available as an 8% dermal patch or cream, can provide pain relief for at least 12 weeks, though application may cause erythema and pain which can be mitigated by applying 4% lidocaine for 60 minutes before capsaicin application 1

Second-Line Treatment Options

• Pregabalin: Consider if patients have inadequate response to gabapentin, with an NNT of 4.93, and effective doses typically ranging from 150-600 mg/day in two divided doses 3, 1

• Opioids: Certain opioids (oxycodone, extended-release morphine, methadone) show efficacy (NNT = 2.67) but should not be used as first-line agents due to risks of pronociception, cognitive impairment, respiratory depression, endocrine/immunological changes, and potential for misuse and addiction 3, 1

• Tramadol: Shows efficacy with an NNT of 4.76 1

Combination Therapy

• When single agents provide inadequate relief, combination therapy such as morphine with gabapentin may be more effective, allowing for lower doses of each medication while providing additive effects 3, 1

Special Considerations for Elderly Patients

• Start with lower doses and titrate more slowly 1
• Topical treatments are particularly valuable due to minimal systemic effects 1
• Monitor for medication side effects, especially somnolence, dizziness, and mental clouding with gabapentinoids 1

Common Side Effects and Management

• Gabapentin: Most common adverse reactions include dizziness (28%), somnolence (21%), and peripheral edema (8%) 2
• TCAs: Monitor for anticholinergic effects, sedation, and cardiac effects 1
• Topical agents: Generally well-tolerated with minimal systemic absorption 1

Prognosis

• PHN is often refractory to treatment and can last for years, causing physical and social disability, psychological distress, and increased healthcare utilization 4
• Patients may experience multiple types of pain including constant deep, aching, or burning pain; paroxysmal, lancinating pain; hyperalgesia; and allodynia 5
• Pain typically improves over time, though some patients may have persistent symptoms requiring ongoing management 1
• Periodic reassessment of continued therapy is recommended as PHN may improve over time 1

Treatment Algorithm

1. Start with first-line agent: Gabapentin, tricyclic antidepressant (preferably nortriptyline), or topical lidocaine patch based on patient characteristics and comorbidities 1, 3
2. If inadequate response after 2-4 weeks: Try alternative first-line agent or add second agent for combination therapy 1
3. If still inadequate response: Consider second-line agents (pregabalin, SNRIs, or carefully selected opioids) 1
4. For localized pain: Prioritize topical agents (lidocaine patch, capsaicin) 1
5. For widespread pain: Systemic medications (gabapentin, TCAs) are more appropriate 1
6. Adjust treatment based on tolerability and efficacy: Monitor for side effects and titrate doses accordingly 2

Important Caveats

• Lamotrigine is not recommended for PHN due to lack of convincing evidence of efficacy and risk of lamotrigine-associated rash 3
• Gabapentin requires dosage adjustment in patients with renal impairment 2
• Preventive gabapentin during acute herpes zoster has not shown significant benefit in preventing PHN 6