A comparison between IV paracetamol and IV metamizol for postoperative analgesia after retinal surgery

Abstract

Objective: To assess clinical efficacy of IV paracetamol 1 g and IV metamizol 1 IV metamizol 1 g on a 24-h dosing schedule in this randomized, double-blinded, placebo-controlled study of 38 ASA physical status I-III patients undergoing retinal surgery.

Research design and methods: General anaesthesia using remifentanil, propofol, and desflurane was performed for surgery. The patients were randomly allocated to three groups, receiving infusions of paracetamol 1 g/100 mL (Para Group), of metamizol 1 g/100 mL (Meta Group), or of 100 mL of saline solution as placebo control (Plac Group) 30 min before arrival in the recovery area and every 6 h up to 24 h postoperatively. All patients had unrestricted access to intravenous opioid rescue medication.

Main outcome measures: The primary efficacy variables were pain scores at rest over 30 h postoperatively analysed by using repeated ANOVA measurement. Secondary efficacy variables were pain scores on coughing, also analysed by repeated ANOVA measurement.

Results: Five patients in the Plac Group and one patient in the Meta Group interrupted the study protocol. Regarding pain scores at rest, Mauchly-test of sphericity was significant (p = 0.03). For the p time effects a significant result was detected (p < 0.001). The main effect between the three treatment groups was significantly different (p = 0.01). The Bonferroni adjusted pair wise comparisons between p the Plac Group and the Para Group showed a significant difference in favour of IV paracetamol (p = 0.024; mean difference 14.8; p 95% CI 1.6-28.0), between the Plac Group and the Meta Group in favour of IV metamizol (p = 0.025; mean difference 14.4; 95% CI p 1.5-27.4), and no significant difference between the Para Group and the Meta Group (p = 1.0; mean difference 0.4; 95% CI-12.8 to 13.6). Pain scores on coughing showed a significant different main effect between the three treatment groups (p = 0.022). The Bonferroni adjusted pair wise comparisons between the Plac Group and the Para Group showed a significant difference in favour of IV paracetamol (p = 0.032; mean difference 17.9; 95% CI 1.3-34.6), a p difference, though not reaching statistical significance, in favour of IV metamizol between the Plac Group and the Meta Group (p = 0.081; p mean difference 15.0; 95% CI -1.4 to 31.4), and no significant difference between the Para Group and the Meta Group (p = 1.0; p mean difference 2.9; 95% CI -13.8 6 to 19.6). None of the patients experienced itching; one patient in the Meta Group developed a mild erythema. There was no statistical difference in the incidence of nausea (Plac vs. Para Group: p = 0.94, Plac vs. Meta Group: p = 0.98, Para vs Meta Group: p = 0.95) or vomiting (Plac vs. Para Group: p = 0.73, Plac vs. Meta Group: p = 0.85, Para vs Meta Group: p = 0.86) between the groups. Patients in the Plac Group experienced significantly more often sedation than patients in the Meta Group (p = 0.049). There was a trend of higher sedation in the Plac Group than in the Para Group, which did not reach statistical significance (p = 0.07). There was no difference in sedation between the Meta and the Para Groups (p = 0.84).

Conclusion: IV paracetamol 1 g has a similar analgesic potency as IV metamizol 1 g for postoperative analgesia after retinal surgery.