Metamizole-associated adverse events: A systematic review and meta-analysis

Background: Metamizole is a pain killer, used in many parts of the world. Studies on the safety profile of metamizole have shown rather strongly different results. Studies with a high level of evidence are missing. Methods: We searched CENTRAL, MEDLINE, EMBASE, CINAHL, and several clinical trial registries. We included randomized controlled trials that compared the effects of metamizole, administered to adults in any form and for any indication, to other analgesics or to placebo. Two authors extracted data regarding trial design and size, indications for pain medication, patient characteristics, treatment regimens, and methodological characteristics. We conducted separate meta-analyses for each metamizole comparator and report results as risk ratios (RRs). The primary end point was any adverse event (AE) during the trial period. Results: We included 79 trials with almost 4000 patients with short-term metamizole use in the inpatient setting (we didn't find any family practice-based trials). Fewer AEs were reported for metamizole compared to opioids. We found no differences between metamizole, other analgesics or placebo. Only a few serious AEs were reported, with no difference between metamizole and other analgesics. No agranulocytosis or deaths were reported. Our results were limited by the mediocre overall quality of the reports. Conclusions: For short-term use in the hospital setting, metamizole seems to be a safe choice when compared to other widely used analgesics. High-quality, adequately sized trials assessing the intermediate- and long-term safety of metamizole in primary care are needed.