Population pharmacokinetics of oral fosfomycin calcium in healthy women.

Background: Fosfomycin is an antibiotic extensively used to treat uncomplicated urinary tract infections in women, and it is available in different salts and formulations. The European Medicines Agency (EMA) recommends further studies to characterize the pharmacokinetics of fosfomycin calcium for oral administration and to justify its dosage recommendation.

Objectives: A population pharmacokinetic model of fosfomycin calcium was developed after oral administration to healthy women.

Methods: A clinical trial (a randomized, open-label, bioavailability study of single and multiple doses of 1000 mg capsules, single dose of 500 mg capsule and single dose of 250 mg/5 mL suspension of oral fosfomycin calcium under fasted conditions in healthy women volunteers, Code: PD7522.22, EudraCT: 2020-001664-28) was carried out at the Clinical Trial Unit, Araba University Hospital (Vitoria-Gasteiz, Spain). Twenty-four healthy women were included in the study, and plasma samples were collected at different times over a period of 24 h. The concentration-time data of fosfomycin in plasma were modelled by a population approach using a nonlinear mixed-effects modelling implemented by NONMEM 7.4 (ICON Clinical Research LLC, North Wales, PA, USA).

Results: The pharmacokinetics of fosfomycin was best described by a two-compartment model. Creatinine clearance and body weight were identified as covariates for fosfomycin clearance and volume of distribution, respectively.

Conclusions: This study provides relevant information on the pharmacokinetic profile of fosfomycin in women after oral administration as calcium salt. This population model may be very useful for establishing dosage recommendations of fosfomycin calcium to treat urinary tract infections in women.