The effect of promethazine on intrathecal morphine-induced pruritus in caesarean section patients

Background: Adding morphine as adjuvant intrathecal drug for cesarean section is a gold standard for post-operative analgesia according to literature, but because of frequent incidence of nausea, vomiting and pruritus, it has limited popularity. Various mechanisms have been demonstrated for the opioid-induced pruritus, with a variety of medications with different mechanisms of actions for prevention and treatment. The aim of this study was to determine the effect of intramuscular promethazine on intrathecal morphine-induced pruritus after cesarean delivery. Methods: In a retrospective descriptive-analytical study, recorded data of two thousand American Society of Anesthesiologists (ASA) I or II women undergoing elective cesarean delivery at the Bahman Hospital of Tehran, Iran, during the period of 2008 to 2013 were reviewed. Participants were divided into two groups of one thousand for each theme; the initial group underwent spinal anesthesia by employing intrathecal morphine as part of a standard anaesthetic regimen without prophylactic administration of promethazine, the subsequent group received 25 mg intramuscular promethazine after intrathecal drug administration. The incidence and severity of pruritus (absent, mild, moderate or severe) and intensity of pain using numeric rating scale (NRS) and also the incidence of nausea and vomiting were examined as main variables. All data were analyzed using SPSS software, version 22 (IBM SPSS, Armonk, NY, USA) and P values of less than 0.05 were considered as statistically significant. Results: The incidence of nausea (P=0.025) and vomiting (P=0.046) was different in two groups; with statistical significance. The mean score of pain according to numeric rating scale (NRS) was similar in both groups (P=0.46). The frequency of pruritus was statistically similar in both groups, (P=0.302); but the severity of itching showed statistically significant difference between two groups (P<0.001). Conclusion: The severity of pruritus was significantly reduced by intramuscular administration of 25 mg promethazine, shortly after spinal morphine administration but it was shown to be ineffective to reduce the incidence of pruritus. Also, the incidence of post-operative nausea and vomiting (PONV) was less by intramuscular promethazine application.