Single Center, Open-label, Prospective Study to Characterize the Pharmacokinetics of Metamizole and Its Metabolites Following Intravenous Administration in Children Less Than 6 Years Old

This is an open-label pharmacokinetics (PK) study. It aims to assess the PK parameters of metamizole and its metabolites following a single IV administration of metamizole (10mg/kg) in children less than 6 years of age.

Thirty-nine children, 3-72 months of age, undergoing elective surgery at the University of Basel Children's Hospital, will receive, on the day of surgical procedure, a single dose of metamizole 10 mg/kg. After this dose, blood and saliva samples will be obtained at predetermined post-dose time points to measure concentrations of metamizole and its metabolites. The maximal duration of subject participation will be 24 hours. Plasma PK parameters (AUC, Cmax, Tmax, t1/2) of each analyte will be derived using noncompartmental methods. A population PK approach will be applied to characterize inter-subject variability and quantify the potential influence of age, sex and body weight on the PK parameters.

There are no published pharmacokinetic studies of metamizole in pediatrics. Furthermore, although Swissmedic provides no dose information for IV administration in infants with a body weight of less than 9 kg, IV is the most frequently used route of administration for direct postoperative analgesia in pediatrics, including infants with body weights of less than 9 kg. Due to the absence of data and the lack of any dosing recommendation for infants with a body weight less than 9 kg, the IV administration of metamizole in infants is "off-label" and inconsistent across hospitals and prescribing paediatricians.