A (72-yeаr-оld mаle with nо cоmorbid medicаl conditions is brought to the ED with a 4-day history of fever, cough, and headache. He also reports abdominal pain, nausea, and diarrhea for the past 2 days. He has no history of smoking or alcohol consumption. Physical exam shows an alert man with poor concentration. Blood pressure is 140/75 mmHg, pulse is 105/min, temperature is 38.9°C (102°F), and respirations are 24/min. Lung examination shows mildly reduced air entry in the left base. Heart sounds are normal. Abdomen is soft with normal bowel sounds and no tenderness on superficial or deep palpation. Complete blood count shows a leukocyte count of 15700/mm3 (13% bands, 77% PMNs, 6% lymphocytes, and 4% monocytes). Chest X-ray shows patchy infiltrates in the left lower lobe. Sputum testing reveals abundant neutrophils with no organisms. Chemistries are significant for Na+ 130mEq/L. A urine legionella antigen is positive. What is the most appropriate pharmacotherapy in this patient?