Due to possible serious adverse drug reactions (ADRs), the use of metamizole for postoperative pain therapy in children is a subject of debate. Safety studies with large sample sizes have not been published as yet.OBJECTIVE
The aim of this study was to evaluate the use of metamizole in children aged up to 6 years undergoing surgery with a particular focus on serious ADRs such as haemodynamic, anaphylactic or respiratory reactions and agranulocytosis.DESIGN
A multicentre, prospective, noninterventional, observational postauthorisation safety study (PASS).SETTING
The study was conducted in six different paediatric centres from September 2013 to September 2014.PATIENTS
One thousand one hundred and seventy-seven children aged up to six years (American Society of Anesthesiologists’ physical status class I to III) receiving a single dose of metamizole for postoperative pain therapy were enrolled.MAIN OUTCOME MEASURES
Patient demographics, main and secondary diagnoses, surgical procedures performed, metamizole dose, haemodynamic data, use of other analgesics and regional blocks, results of pain measurement (Children and Infants Postoperative Pain Scale, ChIPPS) and ADR incidence were documented using a standardised case report form.RESULTS
Of the 1177 children observed at six paediatric centres, 1145 were included for analysis [age 35.8 ± 18.1 (0.1 to 72) months]. The mean metamizole dose was 17.3 ± 2.9 (8.3 to 29.4) mg kg−1. Mean arterial pressure (MAP) remained stable during metamizole infusion [baseline 55.7 ± 11.3 (25 to 98) and after infusion 56.6 ± 11.3 (25 to 99) mmHg; P < 0.01]. Pruritus, swelling and exanthema were observed in one patient each (total 0.3%). No respiratory adverse events directly related to the metamizole administration and no clinical signs of agranulocytosis were reported. All data are mean ± SD (range).CONCLUSION
Single intravenous doses of metamizole used for the prevention or treatment of postoperative pain were well tolerated in more than 1000 children aged up to 6 years. The probability of serious ADRs (haemodynamic, anaphylactic or respiratory reactions) is lower than 0.3%. The sample size and follow-up was not sufficient to detect episodes of agranulocytosis.