Adrenaline Auto-Injector Prescribing in Primary Care in England: An Analysis of Non-Standard Dosing.

INTRODUCTION: The recommended first-line treatment for anaphylaxis in the community is intramuscular injection of adrenaline. The treatment is a standardised dose of either a 150 μg or a 300 μg adrenaline auto-injector (AAI) device depending upon the patient's weight. Currently, no standardised mechanisms exist to transition patients onto the higher 300 μg dose when they reach 25-30 kg (depending upon the manufacturer). METHODS: We undertook analysis of NHS prescriptions data dispensed in the community in England to identify rates of non-standard AAI dose prescribing. Non-standard prescribing is defined as patients who are likely to have exceeded the 25-30 kg threshold but still received a 150 μg dose. Data were limited to the most recent AAI prescription for an individual patient that occurred in the last 2 years (December 2022-2024). Patient weight at the time of prescribing was approximated using an age-to-weight correlation model. AAI recommended switching weights, based on device metadata, were compared to the patients' approximated weight to identify non-standard prescribing. Statistical comparison between rates of non-standard prescribing and patient deprivation was computed using Kendall's Tau correlation coefficient. A complementary analysis to identify patients who received a 300 μg dose but were likely under the 25-30 kg threshold was also carried out. RESULTS: Overall, 46,999 patients were identified as having received a 150 μg strength injector in their most recent AAI prescription; of these, over 95% received two or more devices in line with national guidance. Estimates based on age for weight growth centiles show that between 9480 (20.2%) and at least 1747 (3.7%) of those prescribed a 150 μg autoinjector were likely to exceed the weight threshold for this dose. Using a Resuscitation Council UK guideline of age 6 years for switching to a 300 μg dose, the estimated proportion prescribed a non-standard AAI dose increases to 23,059 patients (49.1%). Estimated rates of non-standard AAI prescribing were found to be higher in areas of England with the most deprivation. Conservative estimates found only 67 children likely under 25 kg and 330 children likely under 30 kg who received a 300 μg dose. CONCLUSIONS: This analysis of community AAI prescriptions in England suggests that underdosing of AAI prescriptions in children and adults is not uncommon. Healthcare professionals with patients at risk of anaphylaxis should review whether patients prescribed AAI devices have the appropriate device for their weight.