Introduction Zoledronic acid (ZA), used for treatment of children with osteoporosis, can cause acute phase reaction (APR) following the first infusion. Many institutions have a policy to admit and monitor all children for their first ZA infusion.

Objective To determine if the APR with the first ZA dose warrants hospital-level care and evaluate if its severity correlates with the underlying condition.

Design Retrospective cross-sectional analysis.

Settings Two tertiary centres across the UK that run paediatric metabolic bone disease services.

Patients Children who received first ZA infusion as inpatients at these centres.

Interventions Nil.

Main outcome measures The Paediatric Early Warning Score (PEWS) and length of hospital stay to assess the severity of APR.

Results 107 patients were included. Peak PEWS≤3 was found in 85% of children. 83% required admission for <24 hours. The various patient populations (osteogenesis imperfecta (OI), immobility-induced osteoporosis, idiopathic juvenile osteoporosis, systemic inflammatory disorders and steroid-induced osteoporosis, Duchenne muscular dystrophy (DMD)) did not differ significantly in the mean peak PEWS and the length of hospital stay. However, when compared directly, the group with DMD and that with systemic inflammatory disorders and steroid-induced osteoporosis differed significantly in the mean peak PEWS (p=0.011) and the length of hospital stay (p=0.048), respectively, as compared with the OI group.

Conclusion Most patients had a mild APR not requiring overnight hospital admission, after their first ZA dose. However, certain groups seem to suffer more severe APR and may warrant consideration of inpatient monitoring with the first infusion.