Topical ketamine gel: Possible role in treating neuropathic pain

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 abse nt. Wind-up is thought to cause allodynia, hyperalgesia, and hyperpathia. R eceptors such as NMDA, AMPA, and M-glu hale recently been identified for th eir role in central sensitization or pain 'windup'. Ketamine has been propo sed recently for neuropathic pain secondary to its NMDA receptor activity. The current application as a topical gel sterns from the theory that ketami ne has peripheral action at both opioid and Na+-K+ channels. This case stud y involved 5 patients from 25 to 70 years old (3 RSD, 1 lumbar radiculopath y, 1 post-herpetic neuralgia). Dose used was determined by site and surface area of involvement and ranged from 0.093 mg/kg to 9.33 mg/kg. All five pa tients reported significant pain relief at initial application and wished t o continue treatment. The average numerical analogue scale (NAS) score prea pplication was 8.8. The average IS minutes post application NAS was 1.6. Pa tients reported alterations in temperature sensation, feelings of relaxatio n and decreased tension in the area of application, and pain relief. Reduct ion in numerical pain scores postapplication of ketamine gel ranged from 53 -100% using a 1-10 numerical pain intensity scale. No significant side effe cts were reported. Ketamine Gel may provide clinicians with a new option in the battle against chronic neuropathic pain. Until further information is available and larger trials can be conducted, we can only recommend this ty pe of therapy for refractory cases in which all primary and secondary optio ns have been exhausted.