Multi-Day Low Dose Ketamine Infusion as Adjuvant to Oral Gabapentin in Spinal Cord Injury Related Chronic Pain: A Prospective, Randomized, Double Blind Trial

Abstract

Background: Severe, intractable, chronic pain is a significant management problem for those involved in the long-term care of spinal cord injury (SCI) patients . Gabapentin, an anticonvulsant, is widely used for treating chronic pain. Ketamine, an NMDA receptor antagonist, has been available in clinical practice for 35 years. Its usefulness in pathological pain states is known. Despite this, no formal research on its effectiveness in treating neuropathic SCI pain exists. Objectives: This double-blind study sought to determine the safety and efficacy of adding a multi-day low dose ketamine infusion to oral gabapentin for treating chronic pain related to post spinal cord injury. Study Design: Randomized, controlled, double blind trial Setting: Hospital, in-patient setting. Methods: Forty patients diagnosed with neuropathic pain secondary to spinal cord injury were randomized into 2 equal groups. Group I received an 80 mg intravenous ketamine infusion diluted in 500 cc normal saline over a 5 hour period daily for one week and 300 mg of gabapentin 3 times daily. Group II received a placebo infusion and 300 mg of gabapentin 3 times daily (continued) after 300 mg of gabapentin 3 times daily. Using the visual analogue scale, pain was assessed prior to treatment, daily following ketamine or placebo infusions for 7 days, and then weekly for one month after infusion termination. Side effects, specifically those related to ketamine or gabapentin, were reported. Results: Both groups demonstrated significantly reduced pain scores compared with pretreatment values (P < 0.05). Group I showed significant pain score improvements over Group II at all measurements (P < 0.0001) during infusion and 2 weeks after infusion termination. There was no statistical difference between the groups at 3 weeks and 4 weeks after infusion termination (P = 0.54 and P = 0.25 respectively). Both drugs were tolerated by all patients; no side effects required intervention. Conclusion: Multi-day low dose ketamine infusion as adjuvant to gabapentin in post-spinal cord injury related chronic pain is safe and efficacious in reducing pain, but the effect compared to placebo ceased 2 weeks after infusion termination. Limitations: Study size limited to 40 patients. Key words: Ketamine, Gabapentin, Spinal, Pain, injury, chronic