Aim To investigate the frequency and characteristics of adverse drug reactions (ADRs) in hospitalised neonates to obtain a better understanding of and improvement in neonatal healthcare.

Methodology A prospective cohort study. Data were collected on 313 neonates and 2166 drug prescriptions. Clinical characteristics of patients, drugs administered and ADRs were prospectively recorded and analysed. Informed consent was obtained in all cases.

Results 116 different ADRs were detected. 17% of the neonates experienced at least one of these ADRs. Systemic antimicrobials and caffeine citrate were the drugs that most commonly caused ADRs. According to the ADR Severity Assessment Scale, 41% were mild, 42% were moderate and 17% were severe. Of the ADRs identified, 11% were classified as ‘certain’ by the Naranjo method and 20% were classified as ‘defined’ by the Karch and Lasagna modified algorithm. Most of the ADRs detected were related to feed intolerance, phlebitis and tachycardia. Most were acute (73%) and lasted between 1 and 7 days (39%). After the occurrence of an ADR, it was necessary to initiate specific treatment in 44 cases, discontinue the drugs involved in 30 cases, and reduce the drug dose in another 30 cases. An association was shown between the number of drugs prescribed and ADR onset.

Conclusions There is a high incidence of ADRs in hospitalised newborns, which increases with the number of prescriptions.