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Most recently a novel, long-acting, injectable formulation
of omeprazole, which is formulated for sustained release, to overcome the short half-life observed following the parenteral administration of traditional formulations, is stable at room temperature for extended durations, and appears well tolerated following i.m. injection, has been described (Sykes et al. 2017a). Following the administration of a total body dose of 2.0 g (equivalent to a dose of 4 mg/kg once per week for a 500 kg horse), marked acid suppression was observed within hours of administration. Pronounced acid suppression (%tpH >4 exceeding 66%) persisted for 4 days in all (6/6) animals, and for at least 7 days in 4/6 animals. Although the pharmacokinetics of the formulation has not been described, the use of a slow release, long-acting formulation overcomes the primary limitation of oral omeprazole, being a very short half-life, which conflicts with the need for the drug to be present when proton pumps are activated throughout the intertreatment interval. Equally, it can reasonably be assumed that the wide degree of variation observed in bioavailability following oral administration is less likely to be present with an i.m. formulation, and this is evidenced by the consistent acid suppression achieved over the 4–7 day period. A pilot clinical investigation of the formulation consisting of
24 horses treated twice at weekly intervals (on Days 0 and 7) and re-examined at Day 14 yielded favourable results (Sykes et al. 2017a). In 22 horses affected with ESGD, healing was observed in 100% of animals. This compares favourably with previous reports of once daily administration of oral omeprazole with a 70–85% healing rate over a 4-week treatment duration consistently reported in the literature (Andrews et al. 1999; MacAllister et al. 1999; Lester et al. 2005; Sykes et al. 2015b). Similarly, in 12 horses affected with EGGD, healing was observed in 75% of animals. This compares favourably with the EGGD healing response rates of only 9– 35% with 28–35 days of oral omeprazole therapy at 4.0 mg/kg once daily that have been reported in a similar population of horses (Sykes et al. 2014a,b, 2015b). Although only a small number of animals were studied in the pilot study, the results of the study suggest that the formulation may be advantageous in the management of ESGD or EGGD cases refractory to oral omeprazole therapy, or where the diet of the individual animal is expected to interfere with the therapeutic response to oral therapy. Further, the use of parenterally administered omeprazole, in lieu of oral medications, as a frontline therapy warrants consideration in animals with overt clinical signs on welfare grounds, due to the rapid and predictable nature of acid suppression achieved with parenteral administration.
Conclusion
Oral omeprazole is currently the cornerstone of the treatment of EGUS. However, greater attention should be given to the impact of feeding on drug absorption and the role of individual dose responsiveness when tailoring treatment plans for individual animals. Several new generation PPIs have been described that likely have a role in the management of EGUS where oral therapy is not possible, or where an inadequate response has been observed with oral omeprazole treatment. It should be emphasised that the use of unregistered medications and off-label dosing should be done in accordance with local regulatory frameworks and best practice guidelines.
Author’s declaration of interests
Two studies reviewed in the current manuscript were funded by Luoda Pharma and Bova Compounding. In addition to a part-time post as an Adjunct Associate Professor with The University of Queensland, B.W. Sykes is employed by Bova Australia, acts as an advisor to Bova UK and is a paid consultant to Luoda Pharma Pty Ltd.
Ethical animal research Not applicable to this article.
Source of funding None.
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