Leucopenia associated with metamizole: a case-control study.

AIMS OF THE STUDY: The aim of this study was to identify possible risk factors for the development of leucopenia associated with metamizole use. METHODS: A retrospective case-control study was performed. Cases of metamizole-associated leucopenia managed at a single centre (2005-2013) were characterised and compared with matched controls who took metamizole without developing complications. RESULTS: Fifty-seven cases and 139 controls were identified. Of the cases, 32 were postoperative and these were compared to age-, sex-and ward-matched postoperative controls (n = 64). The remaining cases (n = 25) were compared to sex-matched, non-postoperative controls (n = 75). The number of patients with a positive allergy history was higher among postoperative cases than controls (p = 0.004) as was the number with previous leucopenic episodes (p = 0.03). The prevalence of diagnosed hepatitis C infection was 9% among all cases compared with 1% among all controls (p = 0.005). The use of concomitant cytostatic agents (even at immunosuppressive doses) was significantly higher among nonpostoperative cases than controls (p = 0.011). There was no association between renal function and the development of leucopenia. CONCLUSIONS: A history of allergies, previous leucopenic episodes, hepatitis C infection and concomitant cytostatic agents are possible risk factors for leucopenia associated with metamizole use.