How to Manage Lower Airway Inflammation

Equine lower airway inflammation can result from both infectious and noninfectious causes. Control of lower airway inflammation resulting from bacterial causes is largely reliant on targeting the primary infectious agent via the administration of antimicrobial drugs. In contrast, control of inflammation resulting from noninfectious causes (e.g. organic dust) typically involves avoidance of the inciting inhaled agents and/or the use of corticosteroids, administered orally, i.v., i.m. or by inhalation.

Although oral medication is the simplest means of corticosteroid administration, it is less efficacious compared with parenterally administered formulations. Prednisolone is the only oral corticosteroid licensed for use in the horse and has proven efficacy in the treatment of equine asthma, especially when combined with environmental control [1,2]. However, experimental studies have also demonstrated the clinical efficacy of orally administered dexamethasone [2,3], the bioavailability of which is greater following a period of fasting [4]. That said, dexamethasone is more commonly administered via the i.v. route, an approach considered the most efficacious (from an anti-inflammatory perspective) in equine asthma, resulting in a rapid (within hours) improvement in lung function [5]. However, there are potential drawbacks to the routine adoption of this approach, most notably significant suppression of blood cortisol levels.

In recent years, the inhaled route of corticosteroid administration has become increasingly popular, with proposed benefits including targeted drug delivery and minimisation of the risks of systemic side effects [6,7]. A dual approach is often adopted in cases with severe lower airway obstruction, whereby an initial short period of dexamethasone administration is then followed by a more prolonged period of inhaled corticosteroid therapy. Until recently, there were no inhaled corticosteroid preparations licensed for use in the horse; consequently, reliance was placed on the ‘off licence’ use of preparations (e.g. beclomethasone and fluticasone) intended for human use. These were generally available as metered dose inhaler devices, with drug delivery achieved via actuation into a face mask or spacer; however, the variability in inhaled drug delivery with this approach was quite large [8,9]. Nebulisation and subsequent inhaled delivery of dexamethasone has also been advocated for the treatment of equine asthma; however, this approach has recently been shown to be nonefficacious [10]. Ciclesonide (a glucocorticoid prodrug) is now licensed for inhaled administration in the horse using a device that generates the drug aerosol via soft mist technology, previously applied in some human inhalational devices. The efficacy of this approach has been shown in both asthmatic horses with experimentally induced disease exacerbation [11] and in a large multicentre field trial [12]. Unlike previously used inhaled corticosteroid preparations, ciclesonide has been shown not to suppress systemic cortisol levels during the duration of treatment.

In summary, corticosteroids remain the mainstay of treatment of nonseptic lower airway inflammation, and the increasing availability of licensed preparations for use in the horse has facilitated this approach to inflammation reduction in this species.

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