Management of Post-Herpetic Neuralgia (PHN) in the Elderly

Background and Why Age Matters

• Constant burning or aching pain (peripheral sensitization and deafferentation)
• Shooting/lancinating pain (ectopic neural discharges)
• Allodynia and hyperalgesia (central sensitization - pain triggered by light touch)

Stepwise Pharmacological Management

First-Line Agents

• Primary: Pregabalin or gabapentin
• Secondary: Lidocaine patch
• Referral: Regional nerve blockade / pain clinic optimization

Second-Line Agents

Third-Line / Adjunct Options

• Carbamazepine, valproate, or SSRIs may further moderate lancinating pain when added to first-line therapy
• Topical combinations: amitriptyline 4% + ketamine 2% cream have been reported for PHN
• Topical capsaicin 0.025-0.075% cream (low-dose, applied 3-4 times daily) - modest benefit; causes initial burning

Special Considerations in Elderly Patients

Pharmacokinetic Adjustments

• Renal function declines with age - gabapentin and pregabalin are renally cleared. Check eGFR before dosing. Reduce doses significantly in CKD.
• "Start low, go slow" titration principle applies to all agents.
• Polypharmacy is common - screen for drug interactions, especially with CNS depressants.

Agents to Use with Extra Caution

• TCAs (especially amitriptyline): The Beers Criteria identifies TCAs as potentially inappropriate in older adults due to anticholinergic effects (delirium, urinary retention, falls, cardiac arrhythmia). If TCAs are used, nortriptyline is the preferred option for its lower anticholinergic profile.
• Opioids: Heightened risk of falls, confusion, respiratory depression, and constipation in the elderly. Use the lowest effective dose and reassess frequently.
• Gabapentinoids: Cause dizziness and sedation - assess fall risk before and during therapy.

Non-Pharmacological and Interventional Options

• Sympathetic nerve blocks: Effective for pain relief during acute zoster and early PHN. Some studies show PHN resolution in up to 80% when blocks are initiated within 2 months of rash onset. Once PHN is well-established, blocks are generally less effective. - Morgan and Mikhail's Clinical Anesthesiology
• Epidural steroid injections: Not proven to prevent or treat established PHN.
• TENS (transcutaneous electrical nerve stimulation): May help some patients, particularly with allodynia.
• Spinal cord stimulation: Considered in refractory cases.
• Psychological support / CBT: Important given the high co-prevalence of depression. Chronic pain management should include assessment and treatment of depression.
• Pain clinic referral: Appropriate for moderate-to-severe, refractory, or complex cases.

Prevention - Critical for the Elderly

• Shingrix (recombinant zoster vaccine, RZV): Strongly recommended for all immunocompetent adults aged 50 and older. Two-dose series (0 and 2-6 months). Highly effective (>90%) at preventing herpes zoster and PHN. This is the preferred vaccine and does not contain live virus, making it suitable for the elderly and most immunocompromised patients. - Morgan and Mikhail's Clinical Anesthesiology
• Prevention of PHN from acute zoster: Early initiation of antiviral therapy (acyclovir, valacyclovir, or famciclovir) within 72 hours of rash onset is recommended for all patients over age 50 with pain or ongoing blistering, as it reduces severity and duration of acute pain and may lessen PHN risk. Antiviral therapy should be started even beyond 96 hours in elderly patients who still have active blisters. - Andrews' Diseases of the Skin

Monitoring and Goals

• Target pain reduction to below 3/10 on NRS, or ≥50% reduction on VAS - a realistic goal achieved in 30-60% of patients with evidence-based pharmacotherapy.
• PHN eventually subsides in most patients, even in persistent cases, although this may take months to years.
• Reassess medication tolerability, fall risk, renal function, and mood (depression) at each visit.
• Refer early to a pain specialist for moderate-to-severe cases or when first-line therapy fails.

Summary Algorithm

Confirm PHN (pain >3 months post-roster) + Assess severity + Comorbidities
        ↓
Start FIRST-LINE (choose based on patient profile):
  - Gabapentinoids (gabapentin/pregabalin) - renal-adjusted
  - 5% Lidocaine patch - preferred if systemic side effects concerning
  - Nortriptyline (low-dose) - if allodynia or depression present
        ↓
Inadequate response (4-8 weeks)?
  → Add or switch to SECOND-LINE:
    - Capsaicin 8% patch (single application)
    - Duloxetine
    - Tramadol or low-dose opioid
        ↓
Still refractory?
  → Refer to Pain Clinic
  → Consider nerve block, spinal cord stimulation, or combination therapy
  → Address depression, psychosocial factors (CBT, support)

• Fitzpatrick's Dermatology, TREATMENT OF POSTHERPETIC NEURALGIA section
• Andrews' Diseases of the Skin, Zoster-Associated Pain section
• Tintinalli's Emergency Medicine, Tables 35-9, 35-10, 38-8
• Adams and Victor's Principles of Neurology, 12th Ed.
• Morgan and Mikhail's Clinical Anesthesiology, 7th Ed.
• Bradley and Daroff's Neurology in Clinical Practice
• US Pharmacist (2025): Optimizing Neuropathic Pain Treatment in Older Adults - NICE-aligned guidelines confirm gabapentin, pregabalin, duloxetine, and TCAs as first-line; "start low, go slow" for elderly

Recent evidence note: A 2023 Cochrane review (PMID 38050854) found corticosteroids during acute zoster do not reliably prevent PHN. A 2023 systematic review (PMID 37629168) covers investigational agents for PHN (e.g., botulinum toxin, tanezumab) that remain under evaluation and are not yet guideline-recommended.