PLE-3260

A previously healthy 24-year-old woman comes to the physician because of a low-grade fever and a nonproductive cough for 7 days. She has been able to continue her daily activities. Her temperature is 37.7 C (99.9 F). A few scattered inspiratory crackles are heard in the thorax. An x-ray film of the chest shows patchy infiltrates in both lungs. Which of the following is the most appropriate initial pharmacotherapy?