Efficacy of tamoxifen for the treatment of severe equine asthma

BACKGROUND: Tamoxifen, a selective estrogen receptor modulator, decreased airway neutrophilia and improved clinical signs in an experimental model of equine asthma, and induced neutrophilic apoptosis in vitro. HYPOTHESIS/OBJECTIVES: Tamoxifen reduces airway neutrophilia and improves lung function in severe asthmatic horses. ANIMALS: Twelve severe asthmatic horses from a research herd. METHODS: Randomized controlled blinded study design. The effects of a 12‐day oral treatment with tamoxifen (0.22 mg/kg, q24h) or dexamethasone (0.06 mg/kg, q24h) on lung function, endoscopic tracheal mucus score and bronchoalveolar lavage fluid cytology were compared. RESULTS: Tamoxifen significantly improved the pulmonary resistance (R (L); mean reduction of 1.15 cm H(2)O/L/s [CI: 0.29‐2.01, P = .007] on day 13), but had no effect on the other variables evaluated. Dexamethasone normalized lung function (mean reduction of R (L) of 2.48 cm H(2)O/L/s [CI: 1.54‐3.43, P < .0001] on day 13), without affecting airway neutrophilia. CONCLUSIONS AND CLINICAL IMPORTANCE: Results of this study do not support the use of tamoxifen at the dose studied as an antineutrophilic medication in the treatment of asthmatic horses in chronic exacerbation.