Hypokalaemia in patients treated with intravenous flucloxacillin: Incidence and risk factors

Hypokalaemia is a potentially life-threatening adverse event of flucloxacillin with unknown incidence. The risk of flucloxacillin-induced hypokalaemia has recently been suggested to be increased among females compared to males. The aim of this study is to describe the incidence and to determine the influence of sex and other risk factors on flucloxacillin-induced hypokalaemia.

A retrospective single-centre cohort study was performed. Patients treated with intravenous flucloxacillin for >24 hours between January 2017 and October 2020, a baseline potassium level of ≥3.5 mmol/L and potassium measurement during treatment were included. The primary endpoint was incidence of hypokalaemia defined as the percentage of patients with a potassium measurement <3.5 mmol/L during flucloxacillin treatment. Logistic regression modelling was used to establish risk factors for hypokalaemia.

A total of 835 patients were included, 58.2% male and median age 71.0 years (interquartile range 61.0-81.0). The incidence of hypokalaemia was 23.7% (28.4% in females vs 20.4% in males). A dose-dependent relation between sex and the incidence of hypokalaemia was found. The risk of hypokalaemia was 4.41 (95% confidence interval 1.47-13.24) times higher in females compared to males when receiving a flucloxacillin dose of >8 g/24 h. No sex differences were found for lower daily doses. Other risk factors for hypokalaemia were older age, concomitant antibiotic use, lower bodyweight, lower baseline plasma potassium concentration and longer treatment duration.

Hypokalaemia is a frequent complication in patients treated with intravenous flucloxacillin. Females receiving >8 g intravenous flucloxacillin per day are more prone to develop hypokalaemia compared to males.