Pharmacodynamic study of a long-acting parenteral formulation of omeprazole in horses.

This research explores a more effective method of treating the common issue of gastric ulcers (EGUS) in horses using a long-acting formulation of the drug omeprazole, known for its inhibitory effects on stomach acid secretion.

Understanding Gastric Ulcers in Horses

• The common cause of gastric ulcers in horses is due to an imbalance of protective and harmful factors in the stomach and duodenal mucosa. The constant secretion of hydrochloric acid contributes to these ulcers.
• Gastric acid in horses is partially neutralized by eating or chewing. However, when a horse stops eating, the gastric pH falls to 2.0 or lower, which increases the susceptibility of the stomach lining to ulcers.
• Particularly, the prevalence of non-glandular or squamous gastric ulceration (EGUS) is high in adult horses, especially those subjected to rigorous training. The drug omeprazol serves as an effective treatment for this kind of ulcer, primarily by inhibiting the secretion of hydrochloric acid.

Limitations of Current Treatment Approaches

• While using H2 receptor-antagonists to inhibit acid secretion has seen success, it requires multiple doses daily and commonly experiences a fluctuating dose-effect relationship, making it unreliable in treating horses.
• Omeprazole is considered a superior inhibitor, but its oral bioavailability is low. This and other issues, such as its clearance rate, limit the drug’s efficacy. Higher dosages of omeprazole are often required in horses than humans, indicating distinctive metabolic interplays.
• An ideal drug formulation still needs to be achieved, given that none of the available preparations consistently maintains the gastric pH above 4.0 in horses.

The Study: A Long-Acting Formulation of Omeprazole

• The researchers developed a long-acting (LA) subcutaneous preparation of omeprazole, containing an omeprazole solution of 30% suspended in a matrix of reverse gel copolymer polyoxypropile–polyoxyethylene (PP/PE).
• The formulation was stable for one week and was stored at temperatures below 4 degrees Celsius. Exposure to this polymer matrix resulted in an extended period of gastric HCl output inhibition.
• Thirty healthy horses under the care of the Mounted Police in Morelia, Michoacan Mexico, were chosen for the study. They ranged from 2 to 19 years of age and weighed between 300 to 550 kg, chosen without prior evidence of gastric ulcers.

Hence, this research provides significant insights on a potential treatment for gastric ulcers in horses that is effective and requires less frequent dosing, by investigating the efficacy of a long-acting preparation of omeprazole.