New Hope for Blind Horses?

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Injectable Omeprazole for Horses

Omeprazole, a substituted benzimidazole and proton pump inhibitor, is used to reduce gastric acid secretion in horses, particularly for treating equine gastric ulcer syndrome (EGUS), which includes equine squamous gastric disease (ESGD) and equine glandular gastric disease (EGGD). ESGD is highly prevalent among horses—especially Thoroughbreds during periods of high-intensity training—while EGGD tends to show a lower healing rate with oral omeprazole, despite reported healing rates of 67–94% for ESGD compared to 9–50% for EGGD. To comply with medication control regulations that prevent horses from racing under the influence of therapeutic drugs, studies have established detection limits and withdrawal times based on pharmacokinetic research using oral formulations, with an international screening limit of 1 ng/mL and a detection time of 48 hours in plasma and unhydrolyzed urine. 

Recent developments in long-acting injectable omeprazole, administered intramuscularly once a week, offer potential advantages such as improved compliance, consistent bioavailability, and avoidance of gastrointestinal variability seen with oral dosing. The pharmacokinetic profile of this novel formulation is complex, characterized by both a fast, first-order absorption from soluble omeprazole and a slower, zero-order infusion from solid-phase omeprazole, sometimes preceded by a lag phase. In some cases, lower drug exposures were observed, possibly due to the formulation being sequestered in tissue. Additionally, the elimination profile displays an initial rapid phase, followed by a slower middle phase as the solid omeprazole dissolves, and finally a terminal phase once complete dissolution is achieved. 

The total clearance of the injectable formulation approximates 15 mL/min/kg—similar to values reported in intravenous studies—indicating near 100% bioavailability, with plasma concentrations generally exceeding those in urine. The steady-state plasma concentration achieved with weekly dosing is around 26.5 ng/mL, and although this overlaps with concentrations observed with oral administration in some studies, the consistently higher trough levels (Cmin) suggest that these lower concentrations drive the clinical effect, possibly explaining the superior healing outcomes observed with the injectable product. However, the extended detection time of over 16 days in both plasma and urine presents regulatory challenges, implying that the long-acting injectable omeprazole may be more appropriate for horses not actively in training. Furthermore, due to the compounded excipients used in this formulation, variability in product quality may affect reproducibility of these results. 

Harding, C., Viljanto, M., Hincks, P., Habershon-Butcher, J. and Paine, S.W. (2025), Plasma and Urine Pharmacokinetics of Long-Acting Injectable Omeprazole Following Intramuscular Administrations to Healthy Thoroughbred Horses. J Vet Pharmacol Therap. https://doi.org/10.1111/jvp.13494 

Bottom line — When this is done clearing regulatory hurdles this might be a good alternative.

Topical Treament for Uveitis in Horses

This study reviews equine recurrent uveitis (ERU), the primary cause of blindness in horses and a spontaneous model for human recurrent uveitis, and investigates a novel immunomodulatory approach using a SOCS1‐KIR mimetic peptide. ERU, characterized by recurrent bouts of intraocular inflammation that progressively damage the eye, mirrors the immunopathology seen in human recurrent uveitis, making the equine model particularly valuable for translational research. The SOCS1‐KIR peptide, designed to mimic a critical inhibitory region of the SOCS1 protein that regulates the JAK/STAT pathway, was shown to reduce immune activation both in vitro and in vivo. Specifically, when applied topically, the peptide significantly diminished the production of inflammatory cytokines such as TNFα and IL‐10 in stimulated peripheral blood mononuclear cells from both healthy and ERU‐affected horses, and lowered cytokine levels in the aqueous humor. Although certain cytokines like IL‐8 increased following treatment, these changes likely reflect complex regulatory feedback within the immune response. Importantly, the treatment was well tolerated even at higher doses and longer durations, reinforcing its potential as a safe therapeutic option. Overall, the findings support further exploration of SOCS1‐KIR as a promising strategy to mitigate the chronic, sight‐threatening inflammation seen in ERU, with implications for treating human uveitis as well. 

Front. Immunol. , 09 January 2025 Sec. Autoimmune and Autoinflammatory Disorders : Autoimmune Disorders Volume 15 - 2024 | https://doi.org/10.3389/fimmu.2024.1513157 

Bottom line — Early results support this as a beneficial treatment

Oral Pimobendan Solution in Dogs

The study confirms that pimobendan is both effective and safe for treating congestive heart failure in dogs, particularly in cases of myxomatous mitral valve disease and dilated cardiomyopathy. It works through a dual mechanism—enhancing cardiac contractility via calcium sensitization and inhibiting PDE3, which also leads to vasodilation—and is available in FDA-approved chewable tablet form. However, achieving accurate dosing with tablets is challenging, especially for small or toy breeds, prompting the development of a liquid formulation that allows for more precise dose adjustments based on body weight. 

The investigation compared the pharmacokinetics and pharmacodynamics of the traditional chewable tablets with a new oral solution containing 1.5 mg/mL of pimobendan. Despite the high variability in pimobendan’s pharmacokinetics, largely attributed to differences in absorption rather than metabolism or excretion, the FDA’s reference scaled average bioequivalence (RSABE) method was used to assess the formulations. This approach, which scales the acceptance criteria to the variability of the drug, along with supporting pharmacodynamic data, demonstrated bioequivalence between the two products. In contrast, the European Medicines Agency’s (EMA) method, which only widens the acceptance range for peak concentration (Cmax) without adjusting the area under the curve (AUC), did not meet the bioequivalence criteria. These results suggest that the EMA’s more rigid criteria may be too restrictive for highly variable drugs like pimobendan, and that a similar scaling approach for AUC might be warranted to ensure clinical equivalence between different formulations. 

Kuhlmann O, Markert M. Pimobendan oral solution is bioequivalent to pimobendan chewable tablets in beagle dogs. J Vet Intern Med. 2025; 39(1):e17248. doi:10.1111/jvim.17248

Bottom line — Bioequivalent to tablets in dogs.

Just putting things in perspective …