A 32-year-old man is evaluated in the office for a 2-month history of fever, night sweats, weight loss, and cough. He works as a pharmacy technician in an extended care facility for veterans. On examination, he has a prominent cough and appears ill. Temperature is 38 °C; other vital signs are normal. Fine crackles are auscultated over the right posterior thorax. The remainder of the physical examination is normal. A chest radiograph shows a right upper lobe infiltrate with a small cavity. A stained sputum specimen is positive for acid-fast organisms; sputum culture results are pending. HIV testing is negative. Which of the following is the most appropriate initial therapy for this patient?