A 20-year-old woman presents to the clinic for evaluation of new symptoms of cough and yellow sputum production. She also reports feeling feverish and having intermittent right-sided chest pain on deep breathing. On physical examination, she appears well and the pertinent findings are dullness on percussion in the right lower lobe and inspiratory crackles on auscultation of the lungs. A chest x-ray confirms there is a right lower lobe infiltrate. Which of the following is the most appropriate treatment of community-acquired pneumonia?