An RCT of 76 patients demonstrated that morphine, with methadone as backup, both reduced the intensity of pain and relieved pain more than placebo.9
Tramadol, a selective opioid agonist, showed moderate effectiveness in a small RCT (N=125), with an NNT of 4.76 (95% CI, 2.61-26.97).3,5,6 The mean pain intensity, degree of pain relief, and amount of rescue medication required were all better in the tramadol group than the placebo group.
Evidence for topical therapy is limited
The anesthetic lidocaine patch 5% has shown efficacy in PHN with allodynia based on 3 RCTs of lower quality (short duration, recruitment of patients who had improved on lidocaine previously, no report of baseline levels of pain); the NNT was 2 (95% CI, 1.4-3.3).10 A systematic review of these 3 RCTs concluded that evidence is insufficient to recommend the lidocaine patch as treatment for PHN.10
Capsaicin, a topical counterirritant, reduced pain in fewer than 20% of patients in 2 RCTs reported in systematic reviews, with an NNT of 3.26 (95% CI, 2.26-5.85).2-6 Blinding was limited in these studies because of the stinging associated with treatment.
Recommendations
A 2004 practice parameter of the American Academy of Neurology recommends TCAs (amitriptyline, nortriptyline, desipramine, and maprotiline), gabapentin, pregabalin, opioids, topical lidocaine, and capsaicin to treat PHN (level of evidence: A), but notes that amitriptyline has significant cardiac effects in the elderly compared with nortriptyline and desipramine.3
In 2006, the European Federation of Neurological Societies determined that TCAs, gabapentin, pregabalin, and opioids had established efficacy (level of evidence: A), but recommended opioids as second-line therapy because of potential adverse events with long-term use.4 The federation’s guidelines designate capsaicin, tramadol, topical lidocaine, and valproate as drugs with lower efficacy or limited strength of evidence (level of evidence: B). Nevertheless, they recommend considering topical lidocaine for elderly patients with allodynia and small areas of pain.4