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 (RL ; mean reduction of 1.15 cm H2 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 RL of 2.48 cm H2 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.