A needle in a haystack: Navigating equine injectable drug reactions

The case report by Vandecandelaere et al. (2026) describing two fatalities following administration of extended-release injectable omeprazole (ERIO) provides an important opportunity to reflect on the inherent risks associated with parenteral drug administration in horses. While these deaths are undoubtedly tragic, it is essential to contextualise this risk within the broader landscape of equine injectable therapeutics to provide balanced clinical guidance. Vandecandelaere et al. (2026) describe two Warmblood horses that developed peracute systemic reactions immediately after intramuscular administration of compounded extended-release injectable omeprazole (ERIO), with one horse recovering and the second dying within 40 min of injection. The reactions developed during or within seconds of injection, with collapse, paddling, tachycardia, dyspnoea and cyanosis, making a causal relationship with the injection event highly likely. Product analysis did not reveal major impurities, although soil-associated organisms were cultured from residual product in the fatal case and the authors discuss inadvertent intra-arterial or subarachnoid injection, anaphylaxis and contamination as potential mechanisms. The author speculates inadvertent intra-arterial administration as being most likely. Commercial sales and pharmacovigilance data from Australia and the UK document over 210,000 units of LAIO have been sold between 2019 and 2025. Within these markets, three deaths have been reported following ERIO injection: the fatal gelding in the case report plus two additional horses that collapsed and died after cervical intramuscular administration, and a further horse that collapsed but recovered fully. One of the three deaths followed an 11-day course of systemic illness associated with a contaminated injection site, representing the development of sepsis rather than a direct pharmacological effect. Even assuming complete administration of all sold doses and underreporting of adverse events, these figures suggest an apparent death prevalence no higher than approximately 1 in 70,000 injections and a very small number of life-threatening nonfatal reactions, which falls within or below the ‘very-rare’ category used in summary of product characteristics (SPCs) for licensed products (