A 58-year-old woman with a history of hypertension presents with a 3-day history of worsening shortness of breath, cough productive of frothy sputum, and bilateral leg swelling. On examination, her respiratory rate is 28/min, heart rate 110/min, BP 160/95 mmHg, and oxygen saturation 90% on air. Crackles are heard bilaterally up to the mid-zones. What is the most appropriate initial pharmacological management?