References
Embracing the Cascade part 3: clinical decision making in equine asthma
Abstract
Equine asthma is the current terminology that covers chronic non-infectious lower airway disorders in the horse. Mild and moderate equine asthma reflect the syndrome previously referred to as inflammatory airway disease, while severe asthma reflects both recurrent airway obstruction and summer pasture-associated obstructive airway disease. Corticosteroids are the most important therapeutic agents for the management of horses with all severities of equine asthma. Prednisolone and dexamethasone products are authorised for use in horses and can be used for the management of asthma. Inhaled corticosteroids have the potential advantages of reduced systemic effects and reduced detection times in competition animals. ‘Special’ (extemporaneous) formulations of oral dexamethasone may be valuable in horses with severe asthma. A range of bronchodilator therapies can be used for the management of severe asthma; although the clinical efficacy of systemic bronchodilators still lacks a robust evidence base, they may have a particular role in ‘rescue-therapy’ and in acute exacerbations. The evidence for the use of mucolytic agents is limited and excessive mucus production should resolve with improvements in airway inflammation. Inhaled saline and inhaled acetylcysteine may provide useful improvements in mucus secretion without any effects on competition horses. Mast cell stabilisers may have a role in the management of mild equine asthma, although they have a limited evidence base for their use. The use of the prescribing cascade provides access to a range of medications that are useful in the management of equine asthma.
Chronic non-infectious lower airway diseases are important causes of clinical and subclinical disease in the horse. Recently the term ‘equine asthma’ has been adopted as a syndrome encompassing inflammatory airway disease (IAD), recurrent airway obstruction (RAO) and summer pasture-associated obstructive airway disease (SPAOD) (Couëtil et al, 2016). This new classification means that most horses classically diagnosed with IAD are now described as having mild/moderate asthma, while those with RAO/SPAOD are usually classified as having severe equine asthma. Irrespective of terminology, the therapeutic principles for horses with equine asthma are environmental management, a reduction in airway inflammation and a reduction in airway obstruction. Therapeutically this involves the use of anti-inflammatory drugs, especially the corticosteroids. Bronchodilator therapies may be of value in the management of horses with severe equine asthma. Other immunotherapies and mucolytic agents may also have a role in the management of affected horses.
The systematic review of the therapeutic options in equine asthma by Ivester and Couëtil (2014) highlights the wide variety of potential therapeutic agents that can be used in such cases. This may include agents that are authorised for the management of allergic airway diseases, as well as medicines that are not authorised for its treatment but can be justified under the prescribing cascade (Figure 1). As described in the previous two articles in the series (Redpath and Bowen 2019a,b), when using medicines under the Cascade, their use should be justified on a case-by-case basis. This article will illustrate the decision-making processes that are applied by the authors when unauthorised medicines are considered in the management of equine asthma. Case examples are presented to demonstrate the decision-making process, and should not be considered as an endorsement of any specific unauthorised product. Readers may interpret the presented evidence differently and may select different treatment regimens based on their clinical judgement. This should not be considered as a ‘violation of the Cascade’ as long as the justifications are based on the clinical need of the individual horse.
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