Topical therapies and combination preparations may have many advantages over orally administered pain relievers, especially for the elderly. Fewer side effects, painless administration and reduced treatment costs are among them. There is growing evidence on the effectiveness and safety of topical agents in a variety of pain disorders, including the most prevalent neuropathic pain conditions.
Neuropathic pain is often resistant to opioids, so other medication classes – such as tricyclic antidepressants, anticonvulsants, and local anesthetics – are often used. Central sensitization, or pain “wind-up”, may perpetuate chronic neuropathic pain even when ongoing peripheral sensory input is absent. Wind-up is thought to cause allodynia, hyperalgesia, and hyperpathia. Receptors such as NMDA, AMPA, and Metabotropic glutamate (mGlu) have recently been identified for their role in central sensitization and antagonists of these receptors have produced pain relief.