Reply to: metamizole for postoperative pain therapy.

Abstract

Editor, We would like to thank Marcel Andrade Souki for his letter about our article ‘Metamizole for postoperative pain therapy in 1177 children’, in which we concluded that 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.1 This article was accompanied by an Invited Commentary by Rollason and Desmeules2 that focused on the controversy whether the analgesic benefit of metamizole was worth the risk of agranulocytosis. We had initiated our observational study in view of ongoing debates in the German Scientific Working Group for Paediatric Anaesthesia (WAKKA) because available data about adverse drug reactions related to metamizole in children are scarce. Our sample size calculation was based on common adverse drug reactions with a suspected frequency less than 0.3% (i.e. haemodynamic, anaphylactic or respiratory reactions) and was hence not sufficient to detect very rare adverse drug reactions (<1/10 000) such as agranulocytosis. Common methods to detect these rare adverse drug reactions are national reporting systems (i.e. pharmacovigilance databases), which are prone to underreporting, in particular of nonlethal cases.3 So far, we have found no published results of such reporting systems indicating the risk of agranulocytosis after single doses of metamizole for postoperative pain therapy in children. Therefore, the present risk seems to be unknown in the paediatric age group; however, there are single case reports of children with (nonlethal) agranulocytosis after multiple metamizole doses for treatment of fever. In accordance with Souki's conclusion, metamizole was evaluated in a recent meta-analysis to be a safe choice for short-term use in the hospital setting, but the authors stated that high-quality, adequately sized trials4 assessing the intermediate and long-term safety of metamizole were needed. Therefore, from our point of view, the decision for or against the use of metamizole for postoperative pain therapy in children should be based on the currently available (rare) evidence, individual risk–benefit evaluations and guidelines of national medical societies. In the present German recommendations for perioperative pain therapy in children, metamizole is strongly recommended, particularly for the perioperative treatment or prevention of acute visceral pain.5 Acknowledgements relating to this article Assistance with the reply: none. Financial support and sponsorship: none. Conflicts of interest: none.