EQUINE VETERINARY EDUCATION / AE / APRIL 2018


215


a)


Beclomethasone dipropionate is one of the most widely


used inhaled glucocorticoids for treatment of human asthma. In horses, beclomethasone use results in marked improvement in respiratory function in horses affected with RAO by decreasing transpulmonary pressure and total pulmonary resistance, and increasing the partial pressure of oxygen (Ammann et al. 1998). In a study by Cou€


etil et al. b)


(2006), RAO challenged horses weighing between 341 and 521 kg, were treated with either low dose beclomethasone dipropionate (500 lg every 12 h) for 10 days or one single injection of dexamethasone isonicotinate (0.06 mg/kg bwt i.m.). After 10 days, the horses treated with the inhaler showed significant improvement in respiratory function, when compared with the horses treated with dexamethasone i.m. No changes in BALF cytology or expression of the proinflammatory transcription factors nuclear factor-jB and activator protein-1 were identified in the horses treated with either dexamethasone i.m. or inhaled beclomethasone dipropionate (Cou€


etil et al. 2006). Even though pulmonary


function testing responses and clinical signs of airway obstruction improve by administration of beclomethasone, the magnitude of response is less marked than the response of i.m. use of dexamethasone when given by daily injections, comparing at Days 7, 10, 14 and 21 of treatment (Rush et al. 1998).


Studies have shown that in horses exposed to a dusty


environment, after discontinuation of inhalation therapy with beclomethasone, clinical signs of RAO return within 7 days if the environmental allergen exposure is not minimised (Rush et al. 1998; Rush 2004). Unlike human patients, horses are more sensitive to the adrenosuppressive effects of aerosolised beclomethasone. Low dose (500 lg) beclomethasone administration caused similar improvement in pulmonary function, compared with high-dose beclomethasone (1000 and 1500 lg), and caused less suppression of endogenous cortisol production (Rush et al. 2000). Adrenal suppression, determined by a decrease in circulating cortisol, is a sensitive indicator of systemic absorption of aerosolised glucocorticoids, and even though the adverse effects of systemic glucocorticoids have not been reported with the use of beclomethasone or fluticasone, these drugs should be used judiciously at the lowest effective dose (Rush et al. 2000; Dıaz et al. 2014; Munoz et al. 2015). Fluticasone propionate is the most potent, most lipophilic,


Fig 1: Delivery devices for the administration of inhaled glucocorticoids. a) AeroHippusTM FlexinebTM


nebulizer.


particles >10 lm will usually stay in the upper airways, whereas submicron-sized droplets are not deposited but exhaled. This diameter will vary depending on the type of inhalation delivery system and the formulation of the drug (Lavoie 2001). Both Equine Haler and AeroHippus consist of hand-held chambers connected to a nose mask that is placed over one nostril and should be held on the nostril for three respiratory cycles to ensure complete inhalation of the dose (Bertin et al. 2011). In contrast, Flexineb equine nebuliser, is a mask type inhaler designed to be used with metered-dose inhalers or wet nebulisation.


hand-held device, and b)


and has the least potential for adrenal suppression of the available aerosolised glucocorticoids (Dauvillier et al. 2011). Reported dosages for fluticasone propionate range between 2–4 lg/kg bwt every 12 h (Ainsworth and Cheetham 2010b), which is about 2000 lg for horses weighing between 410 and


535 kg (Lavoie 2001; Dauvillier et al. 2011). Dosages of fluticasone propionate can vary from 2000 lg up to 6000 lg every 12 h, depending on the severity of the condition and the horse’s bodyweight (Wilson and Robinson 2015). Fluticasone has shown to be effective in prevention and maintenance of RAO; however, for the treatment of acute exacerbations, systemic use of dexamethasone provides a faster and more significant positive effect in pulmonary function (Robinson et al. 2009). Aerosolised glucocorticoids have been shown to induce a


dose dependent suppression of endogenous cortisol in horses suggesting that systemic effects may occur (Rush et al. 1999). Aged horses with a bodyweight between 419 and 550 kg treated with 2000 lg every 12 h of fluticasone for 6 months


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