Pulmonary arterial hypertension is characterized by abnormally high pressure in the pulmonary arteries. Normal systolic pulmonary arterial pressure (PAP) is 25 mm Hg. Clinically affected dogs present with tachypnea, respiratory distress, syncope, and right-sided heart failure. The median survival time after diagnosis is 3 to 3.5 days, the prognosis is grave, and treatment is difficult. Sildenafil citrate has been shown to decrease PAP and pulmonary vascular resistance in humans. The medical records of 13 dogs with pulmonary hypertension treated with sildenafil citrate were reviewed. The median age at diagnosis was 14.5 years. The most common presenting clinical signs included collapse, cough, and respiratory distress, with signs ranging in duration from 3 days to 8 months. An underlying cause was identified in 8 of 13 dogs (chronic pulmonary disease [n = 5], chronic valvular disease with congestive heart failure [n = 1], patent ductus arteriosus [n = 1], and pulmonary thromboembolism [n = 1]). Sildenafil was administered orally at a dose of 1.9 mg/kg Q 8 to 24 H. Concurrent medications as needed were administered. The median PAP was 90 mm Hg; PAP was reevaluated in 8 dogs after therapy, 6 of which had a decrease in PAP (median, 16.5 mm Hg.). Three of 13 dogs were euthanized within 1 day of starting therapy. Ten dogs survived until discharge. Of these 10 dogs, 5 dogs died and 3 were euthanized. Two dogs are still alive. The median survival time of all dogs was 91 days (range, 1-693 days). The drug was well tolerated; two dogs exhibited cutaneous flushing in the inguinal region.

COMMENTARY: Although this study was limited by its retrospective design and small sample size, it appears to support the use of sildenafil for the adjunctive treatment of pulmonary hypertension. Good client communications will help clear the potential confusion about this therapeutic application of the well advertised human drug.

Retrospective evaluation of sildenafil citrate as a therapy for pulmonary hypertension in dogs. Bach JF, Rozanski EA, MacGregor J, et al. J VET INTERN MED 20:1132-1135, 2006.