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Methylnatrexone to prevent intrathecal morphine-induced pruritis after Cesarean delivery
Abstract Number: T 4
Abstract Type: Original Research
Background: Intrathecal (IT) morphine provides excellent and prolonged analgesia following cesarean delivery (CD) however it causes pruritis in over two-thirds of women.(1) N-methylnatrexone bromide, a tertiary derivative of naltrexone, is a peripherally-acting μ-opioid antagonist that does not cross the blood brain barrier, and is FDA-approved to treat opioid-induced constipation.(2) The aim of the study was to assess the effectiveness of subcutaneous methlynatrexone in preventing IT morphine-induced pruritis after CD. We hypothesize that this novel indication for methylnaltrexone will reduce pruritis without adversely affecting post-operative pain.
Methods: A total of 130 women undergoing elective CD are currently being enrolled in this randomized control, double-blinded, multicenter study. All patients receive a standard spinal of hyperbaric bupivacaine12 mg, fentanyl 15 mcg, and morphine 100 mcg. Patients are randomized to receive either a subcutaneous injection of methylnatrexone 12 mg (0.6 ml) or normal saline (0.6 ml) immediately post-delivery. Pruritis, nausea and pain scores are recorded at 2, 4, 8, 12 and 24 h post-study drug. Analgesic, anti-emetics, and anti-pruritics use are calculated for 24 h study period. Overall satisfaction and quality of postoperative recovery are also measured. The primary outcomes are worst pruritis score and the area under the curve pruritis scores for 0-24 h. Naloxone and ondansetron are available to treat pruritis and nausea/vomiting respectively.
Results: At time of abstract submission, we have enrolled 82 of 130 patients in this ongoing study. To avoid unblinding and diminishing the statistical power of the final analysis, we present only descriptive data for the study cohort. 75 (92%) experienced pruritis, and 18 (22%) required treatment for pruritis. The worst pruritis score distribution is outlined in the Figure. 30 (37%). Patients also complained of nausea/vomiting post-CD.
Conclusion: Final unblinded and inferential statistical analysis for this ongoing study will be available for presentation at the upcoming SOAP meeting. If methylnatrexone is effective, this study will provide a viable therapeutic option for a very troublesome side effect, and if ineffective, results will provide valuable mechanistic insight demonstrating that IT opioid-induced pruritis is a centrally, not peripherally, mediated phenomenon.
1. Anaesthesia. 2007; 62(7):672-6.
2. J Pharmacol Exp Ther. 2002; 300(1):118-23.