Background and Importance Isavuconazole is an antifungal drug belonging to the triazole group. It is indicated in invasive aspergillosis and mucormycosis in patients for whom amphotericin B is not appropriate. A rare adverse effect of this drug is hypomagnesemia (from≥1/1,000 to 1/100 cases per patient according to the technical data sheet), which can trigger other electrolyte disturbances such as hypocalcemia or hypokalemia.

Aim and Objectives The aim of this study is to observe the occurrence of hypomagnesemia in a cohort of patients treated with isavuconazole.

Material and Methods Descriptive, observational, retrospective, single-centre, retrospective study, in which all patients over 18 years of age, who were treated with isavuconazole throughout the year 2021, were included. Exclusion criteria were: age less than 18 years, pregnancy or treatment duration less than 24 hours. The main variable under study was the incidence of hypomagnesemia. The variables collected were: sex, age, plasma magnesium concentration before starting treatment with isavuconazole and at the end of treatment, number of days of treatment, need for intravenous magnesium sulfate rescue and concomitant treatment with proton pump inhibitors. A descriptive statistical analysis was performed using measures of central tendency with SPSS v.23®.

Results 37 patients treated with isavuconazole were included. Four patients were excluded. The median age was 63 years (Min-Max, 24–82) and 68% were men. The mean number of days of isavuconazole treatment was 6 ± 4.9 days. Plasma magnesium concentration was measured in 18 (49%) of the patients, of whom 12 were being treated with proton pump inhibitors. The mean plasma concentration before starting treatment was 0.88 ± 0.18 mmol/L, while the mean at the end of treatment was 0.79 ± 0.14 mmol/L. Hypomagnesemia was detected in 17% of patient safter treatment and 11% required rescue with intravenous magnesium sulfate.

Conclusion and Relevance In this observational study of patients treated with isavuconazole, we observed that the occurrence of hypomagnesemia is more frequent than described in the drug technical data sheet. Since hypomagnesemia is a known adverse reaction to the administration of this antifungal drug, and that it can cause other electrolyte alterations, it may be advisable to monitor plasma magnesium levels more closely during the duration of treatment.

Conflict of Interest No conflict of interest