Safety and efficacy of clonidine on postoperative vomiting and pain in pediatric ophthalmic surgery: A systematic review and meta-analysis

Background: Postoperative vomiting and pain are common, unpleasant phenomena in pediatric patients undergoing ophthalmic surgery. Clonidine has antiemetic and analgesic properties and thus may be used as premedication to reduce postoperative vomiting and pain. Aim: To assess whether clonidine premedication may safely decrease postoperative vomiting and postoperative pain in pediatric patients who received an ophthalmic surgery. Methods: We systematically searched PubMed, EMBASE, Cochrane Library, and Scopus databases from their inception to September 2018. Randomized clinical trials comparing clonidine premedication with a placebo or an active comparator that investigated postoperative vomiting or postoperative pain in pediatric patients undergoing ophthalmic surgery were included. The primary outcome was postoperative vomiting. The secondary outcome was postoperative pain. We also evaluated the safety of clonidine premedication by tracking hemodynamic instability associated with its use. Results: Ten studies with 979 patients were eligible for inclusion. Clonidine achieved a significantly lower incidence of postoperative vomiting within 6 hours postoperatively, 6-24 hours postoperatively, and at the end of the study (risk difference: −0.15; 95% confidence interval: −0.32 to −0.05; risk difference: −0.15; 95% confidence interval: −0.29 to 0.01; and risk difference: −0.23; 95% confidence interval: −0.34 to −0.12, respectively) than placebo. For the subgroup of patients who received strabismus surgery, clonidine produced a lower incidence of postoperative vomiting than placebo (risk difference: −0.19; 95% confidence interval: −0.29 to −0.05). Compared to benzodiazepine, clonidine achieved a lower incidence of postoperative vomiting at the end of the study (risk difference: −0.19; 95% confidence interval: −0.31 to −0.07); the effect was only observed in patients receiving clonidine 4 μg/kg. Furthermore, children receiving clonidine had lower postoperative pain scores, lower analgesic requirements, and more of them were pain-free compared to those who received a placebo. No patient using clonidine had any major hemodynamic instability. Conclusion: Compared to placebo or benzodiazepine, clonidine premedication was effective in reducing postoperative vomiting in pediatric patients undergoing ophthalmic surgery. Clonidine premedication also provided more reduction in postoperative pain when compared to placebo. The use of clonidine premedication was not associated with adverse hemodynamic events.