Herpes zoster and postherpetic neuralgia

Prevent zoster with recombinant vaccine, then treat postherpetic neuralgia as localized neuropathic pain: topicals suit small areas and frail patients, and systemic drugs need renal dosing and anticholinergic caution.

1. Allodynia is the signature finding. Pain from a stimulus that does not normally hurt, such as light touch on a healed dermatome, is allodynia; increased pain from a painful stimulus is hyperalgesia ¹.
2. Vaccinate after shingles, once it heals. CDC recommends two doses of recombinant zoster vaccine, 2–6 months apart, for immunocompetent adults 50 and older, whether or not they report prior zoster; there is no specific waiting period other than avoiding vaccination during an acute episode ².
3. Topicals fit localized pain. NeuPSIG 2025 ranks lidocaine 5% plasters and capsaicin as weak second-line options ³; its 2015 version allowed lidocaine first line in frail older patients ⁸. After falls, Beers advises avoiding antidepressants and antiepileptics unless safer alternatives are unavailable ⁷.
4. Know the patch rules. Lidocaine 5%: no more than three patches at a time on intact skin, worn a maximum of 12 hours and then off for 12 ⁴. Capsaicin 8% for postherpetic neuralgia: up to four systems for 60 minutes, no more often than every 3 months ⁵.
5. Systemic first-line drugs need care. Gabapentinoids, SNRIs and TCAs are first-line for neuropathic pain ³. Pregabalin is renally dosed: up to 600 mg/day with normal clearance, 75–300 mg/day at CrCl 30–60 mL/min ⁶.
6. Avoid strongly anticholinergic TCAs in older adults. Beers lists amitriptyline among antidepressants to avoid because it is highly anticholinergic, sedating and causes orthostatic hypotension ⁷.

In older adults with falls, glaucoma or cognitive impairment, systemic choices carry real harm: avoid strongly anticholinergic TCAs, and start gabapentinoids low after checking renal function ⁶⁷.

• Recombinant zoster vaccine is a two-dose series given 2–6 months apart ².
• A prior zoster episode is not a reason to skip or delay vaccination once healed ².
• Lidocaine patch absorption rises with treated area and wear time ⁴.
• Capsaicin 8% reduces TRPV1-expressing nerve endings, which re-emerge over months ⁵.
• Pregabalin at CrCl 15–30 mL/min: 25–150 mg/day; below 15: 25–75 mg/day ⁶.
• NeuPSIG 2025: capsaicin 8% patches, capsaicin cream and lidocaine 5% plasters are weak second-line options; lidocaine evidence is very low certainty ³.
• Hyperpathia is an abnormally painful, often explosive reaction, especially to repeated stimulation ¹.
• Capsaicin 8% must not be applied to broken skin; staff wear nitrile gloves during application ⁵.

• Waiting a year after shingles before vaccinating ².
• Calling light-touch-evoked pain "hyperalgesia" ¹.
• Using the diabetic-foot capsaicin time (30 minutes) for postherpetic neuralgia ⁵.
• Starting pregabalin at full dose without checking creatinine clearance in an older adult ⁶.