Topical ophthalmic atropine in horses, pharmacokinetics and effect on intestinal motility

Pain scoring systems in hospitalized horses with ocular disease

BACKGROUND

Pain recognition in hospitalized horses is challenging, and the utility of pain scoring systems in horses with ocular disease has not been well-described.

HYPOTHESIS/OBJECTIVES

Evaluate the horse grimace scale (HGS) and behavior pain score (BPS) in hospitalized horses with ocular disease. We hypothesized that HGS and BPS would be associated with different clinical progressions.

ANIMALS

Privately owned horses hospitalized for ocular disease between September 2018 and September 2020.

METHODS

Retrospective observational study. The HGS and BPS were recorded daily throughout hospitalization. Clinical progressions were categorized as: (a) discharge from hospital after medical treatment, (b) ophthalmic surgery (eg, keratectomy, conjunctival flap, amniotic membrane transplantation, corneal transplant), or (c) enucleation. Temporal trends in HGS and BPS were assessed using linear regression. Correlations among slope, intercept, and progression were determined using the Kruskal-Wallis test.

RESULTS

Of 65 horses that met inclusion criteria, 29 (45%) were discharged after exclusively medical management, 28 (43%) underwent ophthalmic surgery, and 8 (12%) underwent enucleation. Two horses (3%) had 2 ophthalmic surgeries performed. The BPS scores at admission were higher in horses that were managed medically than in those that underwent enucleation (P = .01). Horses requiring enucleation had higher increases in HGS (P = .02) and BPS (P = .01) during hospitalization than horses that were medically managed and a higher increase in BPS (P = .04) than horses that required ophthalmic surgery.

CONCLUSIONS AND CLINICAL IMPORTANCE

Pain scoring may represent a useful tool for monitoring progression and response to treatment in hospitalized horses with ocular disease.

Plasma atropine concentrations associated with decreased intestinal motility in horses

Introduction

Atropine is an essential part of the treatment protocol for equine uveitis. Topical atropine administration has been associated with decreased intestinal motility and abdominal pain in horses. Experimental studies have indicated that frequent dosing is associated with a higher risk than dosing every 6 h. Unfortunately, no quantitative pharmacodynamic data for inhibition of the equine gut are published.

Materials and methods

Eight standardbred horses were assigned to receive either atropine or saline (control) to be infused over 30 min in a two-treatment cross-over design. Atropine concentrations in plasma were measured using ultra-high-performance liquid chromatography–tandem mass spectrometry. Intestinal motility was measured using borborygmi frequency and electrointestinography (EIG). Experimental data were analyzed using a non-linear mixed effects model. The model was then used to simulate different dosing regimens.

Results

Atropine significantly decreased borborygmi response and EIG response. Six horses developed clinical signs of abdominal pain. The pharmacokinetic typical values were 0.31, 1.38, 0.69, and 1.95 L/kg·h for the volumes of the central, the highly perfused, the scarcely perfused compartments, and the total body clearance, respectively. The pharmacodynamic typical values were 0.31 μg/L and 0.6 and 207 nV²7 cpm for the plasma concentration at 50% of the maximum response and the maximum response and the baseline of cecal EIG response, respectively. Six different dosing regimens of topical atropine sulfate to the eye (0.4 and 1 mg every hour, every 3 h, and every 6 h) were simulated.

Conclusion

The IV PK/PD data coupled with simulations predict that administration of 1 mg of topical atropine sulfate administered to the eye every hour or every 3 h will lead to atropine accumulation in plasma and decreased intestinal myoelectric activity. Administration every 6 h predicted a safe dosing regimen in full-sized horses. Clinical studies would be valuable to confirm the conclusions. For smaller equids and horses put at risk for colic due to othercauses, droplet bottles that deliver 40 μl of 1% atropine sulfate per drop or less may be used to lower the risk further.

Infectious Uveitis in Horses and New Insights in Its Leptospiral Biofilm-Related Pathogenesis

Uveitis is a sight-threatening eye disease in equids known worldwide that leads to considerable pain and suffering. By far the most common type of uveitis in Germany and neighboring countries is classical equine recurrent uveitis (ERU), which is caused by chronic intraocular leptospiral infection and is the main cause of infectious uveitis in horses. Other infectious causes are extremely rare and are usually clinically distinguishable from ERU. ERU can be treated very effectively by vitreous cavity lavage (vitrectomy). For proper indications of this demanding surgery, it is necessary to differentiate ERU from other types of uveitis in which vitrectomy is not helpful. This can be conducted on the basis of anamnesis in combination with ophthalmologic findings and by aqueous humor examination. During vitrectomy, vitreous material is obtained. These vitreous samples have historically been used for numerous etiologic studies. In this way, a chronic intraocular leptospiral infection has been shown to be the cause of typical ERU and, among other findings, ERU has also been recognized as a biofilm infection, providing new insights into the pathogenesis of ERU and explaining some thus far unexplainable phenomena of ERU. ERU may not only have transmissible aspects to some types of uveitis in humans but may also serve as a model for a spontaneously occurring biofilm infection. Vitreous material obtained during therapeutically indicated vitrectomy can be used for further studies on in vivo biofilm formation, biofilm composition and possible therapeutic approaches.

Effect of Topical Cyclopentolate 1% on Ocular Ultrasonographic Features, Intraocular Pressure, Tear Production, and Pupil Size in Normal Donkeys (Equus Asinus)

This study was performed to investigate the effects of cyclopentolate on ultrasonographic parameters of eye structures, intraocular pressure (IOP), tear production, and pupil size in normal donkeys. Sixteen eyes of eight clinically healthy adult donkeys (2-2.5 years old) weighing 295 ± 34 kg (mean ± standard deviation) were used in this study. Cyclopentolate hydrochloride 1% was instilled in a randomly selected eye and the other eye received normal saline drops as a control. The effect of cyclopentolate was evaluated by ultrasonography. Additionally, changes in IOP and tear production were evaluated for 2 hours post-instillation by tonometry and Schirmer tear test (STT), respectively. Vertical and horizontal pupil diameters were recorded pre-instillation (0), and 15, 30-, 45-, 60-, and 120-minutes post-instillation. After cyclopentolate 1% instillation, iridocorneal angle and width of the entry of ciliary cleft were significantly increased as observed by ultrasonography. IOP was significantly increased starting from 30 minutes till 60 minutes post-instillation of cyclopentolate 1%. Non-significant alteration in the STT was observed in the cyclopentolate-treated eyes compared to the control eyes. Both vertical and horizontal pupil diameters began to significantly increase 30 minutes after cyclopentolate 1% instillation compared to the control saline group. In conclusion, cyclopentolate 1% could be used as a potent cycloplegic drug in donkeys without systemic or ocular side effects.