A patient with postherpetic neuralgia confined to the T4 dermatome scores 7/10 on NRS despite pregabalin 300 mg/day. Which adjuvant analgesic has the strongest evidence as a topical agent for localised neuropathic pain?
- A Topical diclofenac 1% gel
- B Topical capsaicin 0.025% cream applied twice daily
- C Topical lidocaine 5% patch (lignocaine patch) ✓
- D Topical ketamine 10% gel
Explanation
Topical lidocaine 5% (lignocaine) medicated plasters are approved and have strong evidence specifically for localised postherpetic neuralgia (PHN), providing peripheral analgesia by stabilising sodium channels in sensitised afferent nociceptors in the affected dermatome without significant systemic absorption. They are particularly suitable when the neuropathic area is well-defined and superficial. High-concentration capsaicin 8% patches (not 0.025%) also have evidence in PHN but carry application site burning and require clinical supervision. Topical diclofenac is for musculoskeletal/osteoarthritis pain, not neuropathic pain. Topical ketamine lacks adequate RCT evidence for PHN.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.