Which one is more efficient on propofol 2% injection pain? Magnesium sulfate or ondansetron: A randomized clinical trial

Background: Painful sensation has been reported after propofol injection in most of the patients but no definite mechanism for this painful sensation has been proposed yet. The present randomized clinical trial compares analgesic effect of ondansetron, magnesium sulphate (MS) and placebo on patients after propofol 2% injection.
Materials and Methods: The present randomized clinical trial with parallel design was performed on 90 patients American Society of Anesthesiologists I-II undergoing general anesthesia within vitrectomy operation with propofol induction. Subjects were randomly allocated into three groups with 30 patients each: (1) MS group (2) ondansetron group and (3) normal saline (NS) group as placebo group. Anesthesia induction and maintenance were the same between groups. Pain intensity of propofol injection in subjects was assessed by a four-point scale (none 0, mild 1, moderate 2 and severe 3) at four time intervals (5, 10, 20 and 25 s) after injection.
Results: MS and ondansetron had significant impacts on pain reduction after propofol 2% injection in comparison with NS as placebo. Comparing two trial groups did not have any significant priority for analgesic impact.
Conclusion: Using ondansetron or MS had no priority on each other on declining propofol injection induced pain.