Background An adverse drug event (ADE) is a potentially harmful and unintended outcome of medicines use. In the UK, ADE trigger tools have been advocated for detecting ADEs associated with high risk drugs, including opioids. Naloxone is used to reverse opioid toxicity so is a useful indicator of potential opioid related ADEs.

Purpose We aimed to measure the sensitivity of naloxone as a trigger to detect opioid related ADEs in adult inpatients in an acute hospital. The objectives were to: assess the positive predictive value (PPV) of the naloxone trigger; and identify drugs most commonly associated with ADEs.

Material and methods We conducted a retrospective review of adult inpatients administered naloxone between October 2014 and September 2015. Naloxone doses recorded as administered on our electronic prescribing system (EPMA) were included. A&E, paediatrics and critical care units were excluded. Ethics approval was not required. Case review forms were completed for each patient and reviewed by a multidisciplinary panel who applied the WHO Uppsala Monitoring Centre Causality Assessment System (WHO-UMC CAS) to confirm opioid ADEs. The National Coordinating Council for Medication Error Reporting and Prevention (NCC MERP) Index was applied to assign a severity of harm rating to confirmed ADEs.

Results 142 naloxone trigger events were identified; 17 were excluded. 125 ADEs were categorised by the multidisciplinary panel using the WHO-UMC CAS tool. 91 cases were considered certain (54), probable (13) or possible (24). 34 cases were considered unlikely (8), conditional (1) or unassessable (25). NCCMERP Index harm ratings were applied to the 91 confirmed ADEs: 90 were categorised as E and 1 event which resulted in escalation of care was categorised as F.

Conclusion The PPV of naloxone for opioid ADEs was 72.8% (91/125). This is higher than in other studies which have found rates of 57.6–68.3%, although methodologies vary. Morphine sulphate was most commonly associated with ADEs, accounting for 55/91 ADEs. Incomplete documentation of patients’ clinical status before and after naloxone administration limited case note review. Although time consuming, our methodology could become the gold standard for confirming opioid related ADEs.

References and/or acknowledgements 1. The Uppsala Monitoring Centre. The use of the WHO-UMC system for standardised case causality assessment. 2012.

No conflict of interest