Utility of lidocaine as a topical analgesic and improvements in patch delivery systems

Interest in and use of topical analgesics has been increasing, presumably due to their potential utility for relief of acute and chronic pain. Topically applied agents with analgesic properties can target peripheral nociceptive pathways while minimizing absorption into the plasma that leads to potential systemic adverse effects. Clinical trials have found 5% lidocaine patches to be effective and well tolerated for the treatment of post-herpetic neuralgia (PHN) with a minimal risk of toxicity or drug-drug interactions. With this patch formulation, the penetration of lidocaine into the skin produces an analgesic effect without producing a complete sensory block. Use of topical lidocaine is supported by clinical practice guidelines, including first-line treatment by the American Academy of Neurology (guidelines retired 2018), the European Federation of Neurological Societies and second-line by the Canadian Pain Society. FDA approved 5% lidocaine patches in 1999, and a 1.8% topical lidocaine system in 2018 - both indicated for the treatment of pain secondary to PHN. The 1.8% system offers a more efficient delivery of lidocaine that is bioequivalent to 5% lidocaine patches, but with a 19-fold decrease in drug load (i.e., 36 mg versus 700 mg) as well as superior adhesion that allows the patch to maintain contact with the skin during the 12-h administration period. Although topical lidocaine formulations have advanced over time and play an important role in the treatment of PHN, a variety of other conditions that respond to topical lidocaine have been reported in the literature including PHN, lower back pain, carpal tunnel syndrome, diabetic peripheral neuropathy, and osteoarthritis joint pain. Other neuropathic or nociceptive pain syndromes may respond to topical lidocaine in select cases and warrant further study. Clinicians should consider local anesthetics and other topical agents as part of their multimodal treatments of acute and chronic pain.