Cardiorespiratory and anesthetic effects of clinical and supraclinical doses of alfaxalone in dogs.

OBJECTIVE To determine the cardiorespiratory and anesthetic effects of 2, 6, and 20 mg kg(-1) IV alfaxalone in hydroxypropyl beta cyclodextrin (Alfaxan) in dogs. STUDY DESIGN Blinded four-way crossover randomized by dose. ANIMALS Eight healthy adult purpose-bred mixed breed dogs (four male, four female) weighing between 12 and 28 kg. METHODS Four (0, 2, 6, 20 mg kg(-1)) IV treatments of alfaxalone were administered to each dog with a 3-hour washout period between doses. Measurements of heart rate, aortic systolic, mean, and diastolic blood pressures, pulmonary arterial and right atrial mean pressures, cardiac output, respiratory rate, tidal and minute volumes, and arterial blood pH, blood gases (PaO(2), PaCO(2)) were performed prior to and at predetermined intervals after drug administration. Systemic vascular resistance and rate pressure product were calculated. The quality of induction, maintenance, and recovery from anesthesia were categorically scored as was the response to noxious stimulation. RESULTS The administration of alfaxalone resulted in dose-dependent changes in cardiovascular and respiratory parameters. Decreases in arterial blood pressure and increases in heart rate occurred at higher doses with most variables returning to baseline in 15-30 minutes. Respiratory rate, minute volume, and PaO(2) decreased and apnea was the most common side effect. The duration of anesthesia increased with dose, and induction, maintenance, and recovery were judged to be good to excellent with all doses studied. CONCLUSIONS AND CLINICAL RELEVANCE Alfaxalone produced good to excellent short-term anesthesia in unpremedicated dogs. Cardiorespiratory effects were minimal at lower doses. Anesthesia was judged to be good to excellent and associated with unresponsiveness to noxious stimulation for the majority of anesthesia. Hypoventilation and apnea were the most prominent and dose-dependent effects.