Epidural coadministration of ketamine, morphine and bupivacaine attenuates post-herpetic neuralgia--a case report.

The N-methyl-D-aspartate (NMDA) receptor system plays an important role in nociceptive signal modulation in the central nerve system. There is considerable evidence that NMDA receptor antagonists can abolish hypersensitivity of nociceptors in animal models. In this case report, we described a patient who suffered post-herpetic neuralgia with severe pain, allodynia, and hyperesthesia over right side T2 to T8 dermatomes. Treatment with conventional doses of non-steroid anti-inflammatory drug (NSAID), antidepressant, anticonvulsant and benzodiazepine failed to provide satisfactory pain relief. With the patient's consent, we administered subanalgesic doses of ketamine (10 mg), morphine (1 mg), and 6 ml bupivacaine (0.1%) through the thoracic epidural route. After the treatment, hyperalgesia and allodynia improved dramatically, and the receptive field also reduced. After four weeks' treatment, satisfactory pain relief was achieved with conventional analgesics treatment. The combination of relatively low doses of morphine, ketamine and bupivacaine epidurally provides effective pain relief in this case. The result strongly suggests a synergy from this combination that warrants a formal study of the dose-response relationship involved in this treatment and the mechanism by which this effect is achieved. This regimen provides a promising treatment for the neuropathic pain with limited side effects.