Background Obesity is a major area of public health concerns, since it is associated with a wide range of se-rious health complications, including diabetes type 2, musculoskeletal disorders, sleep apnea, depression, asthma, hypertension, and cancer. Consequently, obese children are more likely to receive drug treatment than their normal weight peers. Further, obesity is known to be associated with changes in pharmacokinetics of drugs (1–5). Dosing overweight (OW) and obese (OB) children by the use of traditional paediatric dosage strategies (e.g. mg per kilogram or fixed dose by age) may therefore result in a potential risk of sub-or supra-therapeutic doses. We aimed to investigate currently applied dosage strategies in OW/OB children, in a clinical treatment facility. In par-ticular, whether dosage guidelines were used and metrics of body size applied with special attention to drugs with a narrow therapeutic interval and/or loading dose of clin-ical importance.

Methods A retrospective cohort study conducted at the Children’s Obesity Clinic in Denmark, in the period 2008–2015. OW/OB children≤18 years, having at least one drug prescribed, were included. 200 patient records were reviewed. The study was approved by the Data Protection Agency (BBH-2014–045, I-suite 03045)

Drug treatments/prescriptions were registered with ref-erence to the Anatomical Therapeutic Chemical (ATC) Classification System. Dosage strategies were registered as dosage by total body weight (TBW), fixed dose by age (years), use of adjusted weight measures (e.g. IBW, ABW) or dose estimation by other strategies.

Results A total number of 455 prescriptions were iden-tified, primarily distributed in ATC groups N, A, R and J. Guidelines for dosage of OW/OB children were not avail-able in the clinic, for any of the recorded drugs. Only one prescription of gentamicin was adjusted by weight (ABW) using metrics of body size. Otherwise, gentamicin was dosed after three different dosage regimens. In 35/455 prescriptions, dose was adjusted by an undocumented dosage strategy. Dose was primarily limited to the max-imum recommended adult dose, when dose (mg/kg) exceeded adult dose, i.e. acetaminophen.

Conclusion This study highlights the shortage of dos-age guidelines in OW/OB children. We found as suspect-ed a large inter-individual variability in dosage regimens even in drugs with narrow therapeutic intervals or drugs which has loading doses important for clinical effects. The clinicians are left with ‘best practice’, as evidence based dosage regimens are missing for several drugs prescribed during childhood.