Do inhaled or oral glucocorticoids more effectively control feline asthma?

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Appraisal, application and reflection

All three studies used a reduction in airway resistance and reduction in airway eosinophilia as measures of treatment success (Verschoor-Kirss et al. 2021; Leemans et al. 2012; and Reinero et al. 2005).

Pulmonary function testing of asthmatic cats offers a non-invasive means of assessing response to therapy, and in the study by (Leemans et al. 2012) barometric whole-body plethysmography was used in unrestrained conscious cats to assess changes in airway resistance. In contrast, Reinero et al. (2005) and Verschoor-Kirss (2021), anaesthetised cats before airway challenge commenced and the airway’s response was assessed. Leemans et al. (2012) and Reinero et al. (2005) did not find a significant difference in the reduction of airway resistance among treatment groups. Meanwhile Verschoor-Kirss (2021) found that there was a greater reduction in airway resistance with oral glucocorticoid treatment compared to baseline than with inhaled therapy. Although this study does highlight that cats in the inhaled treatment group started with higher baseline resistance than those in the oral group.

Regardless of the study design all studies found that when an oral or inhaled therapy was used, treatment resulted in a reduction in airway eosinophilia. However, only Leemans et al. (2012) found the decrease in BAL fluid eosinophil percentage to be more significant with oral therapy compared to inhaled therapy alone. Interestingly, when salbutamol was used concurrently with the inhaled therapy in this study, they found a significant decrease in BAL fluid eosinophil percentage also (Leemans et al. 2012).

An additional method that was used to evaluate treatment response in the asthmatic cat cohorts, was the change in radiographic appearance of the lungs (determined by a clinical score). Verschoor-Kirss (2021) and Leemans et al. (2012) used changes in the radiographic appearance of the lung as a study outcome. Thoracic radiographs were assessed before and after treatment administration and assigned a score. However, no significant difference was detected between scores before or after oral or inhaled treatment in either study.

Two of the three papers chose to assess fluticasone propionate as the inhaled glucocorticoid and prednisolone as the oral glucocorticoid (Verschoor-Kirss et al. 2021; and Leemans et al. 2012) whilst Reinero et al. (2005) assessed flunisolide and prednisone. Despite two of the studies using the same medications, they were not cross comparable as the doses of the drugs, and length of time for which cats received the oral and / or inhaled glucocorticoid treatment varied greatly. Treatment duration varied from 4 days (Leemans et al. 2012) to 8 weeks (Verschoor-Kirss et al. 2021). Future studies could consider using varying concentrations of each treatment on the same study population to determine the minimum effective dose to control clinical signs associated with asthma.

Verschoor-Kirss et al. (2021) was the only study that assessed a population of naturally asthmatic cats. Clinically their response to treatment is more likely to reflect that of owned asthmatic cats. The treatment protocol in this study differed from the other studies; oral glucocorticoid treatment was given concurrently with the inhalant therapy for 1 week before inhalant therapy was continued exclusively. Whilst this makes it more difficult to determine the efficacy of fluticasone as a sole therapy, this treatment protocol is more likely to be reflective of a feline asthma treatment protocol prescribed in general practice.

All the clinical studies had low numbers of feline participants and study duration was short. The small cohort numbers reduce the statistical power of each paper’s results and consequently make it difficult to draw confident conclusions. Power analysis would be beneficial before performing further prospective, randomised, blinded studies.

Overall, there is a weak pool of evidence available to determine if oral or inhaled glucocorticoid treatment is more effective at managing the airway inflammation associated with feline asthma.

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