Study: Omeprazole Linked to Modest Increase in EIPH

The cumulative effects of the equine gastric ulcer treatment and preventative omeprazole has been linked to a modest increase in incidences of exercise-induced pulmonary hemorrhaging, according to study published this month in the Journal of the American Veterinary Medical Association. "Cumulative omeprazole dose in the preceding 30 days was associated with an increased hazard of EIPH detection," stated the discussion of the study reviewing Hong Kong race records from two different seasons. "Although the estimated strength of the association was not strong, the estimated population attributable fraction of approximately 11% suggests that a modest proportion of the EIPH incidence rate may be attributable to omeprazole exposure under a causal interpretation. "Clinically effective omeprazole doses for equine gastric ulcer syndrome vary according to lesion type and treatment conditions, as well as the formulation. In Thoroughbred racehorses, doses as low as 1 mg/kg once daily of enteric-coated omeprazole have been reported to be as effective as 4 mg/kg once daily for treatment of squamous ulceration when administered before exercise after a brief fast," the discussion continued, noting that in this study the average daily dose was approximately 2 mg/kg/day in a horse weighing 480-500 kilograms (1,060-1,100 pounds). "However, these data do not identify a cumulative dose threshold that can be considered free of EIPH risk," the discussion stated. The study also looked at potential connections with fractures and atrial fibrillation and found no evidence of a relationship with omeprazole use. EIPH, commonly known as bleeding in racehorses, refers to a condition in which capillaries in the lungs rupture during racing and intense training. The study also looked at epitaxis, which is when there is blood visible in the nostrils. Epitaxis, EIPH, atrial fibrillation, and fracture were the focus of this study conducted in Hong Kong because they are major health concerns to horses and can cause substantial economic costs due to lost training and racing opportunities. The analysis reviewed the records of 2,924 horses racing and/or training in Hong Kong in two racing seasons: 2012-13 (1,369 horses) and 2022-23 (1,555 horses). There was no crossover in the horses used in the study between the periods. Omeprazole was analyzed because it is widely used and there have been no studies looking at the potential long-term physiological consequences of using the medication. Omeprazole is known as a proton pump inhibitor, a class of medication that reduces stomach acid and in humans has been associated with an increased risk of fractures due to evidence of micronutrient deficiencies in magnesium and calcium and impaired vitamin B12 absorption. The frequency of endoscopic exams did vary among the 31 trainers managing the horses in training. Statistical analysis of the data in this retrospective cohort study shows a very slight increase in hazard ratio among trainers who conducted more frequent exams. The study did find that horses administered 4 mg/kg once daily in a 1,100-pound horse was "associated with substantial predicted increase in cumulative probability of EIPH detection." Also the study found under a hypothetical scenario in which no omeprazole was administered to the study population that the incidence of EIPH would be estimated to be 11% lower.