Effects of intrarectally administered omeprazole paste on gastric fluid pH in healthy adult horses.

The study investigates the effects of an omeprazole paste administered via the rectum on the pH levels of the gastric fluid in healthy adult horses. It aims to understand how this method could serve as a viable alternative to oral administration, offering better bioavailability and efficacy.

Overview of Omeprazole

• Omeprazole is a medication that helps reduce gastric acid production. It does this by binding and inhibiting H+K+ATPase, an enzyme found in the gastric parietal cells that are responsible for acid secretion.
• When gastric acid secretion slows down and the bore of the digestive system has a pH level above 4.0, it assists in treating and preventing Gastro-oesophageal reflux disease (GERD).
• A similar condition to GERD, known as equine gastric ulcer syndrome, is common in horses. The treatment for this condition involves suppressing acid production and raising the pH level of the gastric fluid, which is why omeprazole is commonly used.

Issues with Oral Administration

• The bioavailability of omeprazole post oral administration is quite low, approximately 40%. This is because the drug is not very stable in acidic gastric fluid and it undergoes first-pass metabolism.
• First-pass metabolism refers to the drug being metabolized by the liver before it can reach the systemic circulation, reducing its effectiveness.
• Alternative oral formulations have been attempted, such as enteric-coated acid-resistant capsules, which can prevent the degradation of omeprazole in the stomach. However, bioavailability limitations persist.
• Oral administration is also often contraindicated in horses with issues such as gastric reflux, difficulty swallowing, choke, or facial fractures. These conditions either make oral administration problematic or potentially harmful.

Rectal Administration as an Alternative

• Rectally administered omeprazole can bypass the challenges posed by the stomach environment and the first-pass metabolism, making it potentially more effective.
• This study specifically tested a commercially available omeprazole paste administered rectally to see its effect on gastric fluid pH in healthy adult horses and assessed its pharmacokinetics.

Study Methodology

• Ten healthy adult horses of varying breeds and ages were part of the study, sorted into two groups.
• Horses in group A were administered a rectal dose of omeprazole paste once daily for five consecutive days. Group B horses received no treatment.
• Baseline samples were collected before the first dose, and blood samples were gathered at different intervals after the final dose. These were analyzed to study the presence and effect of the medicine.