The combination of clarithromycin, ethambutol, and rifabutin is the most appropriate treatment for this patient who has AIDS and a disseminated Mycobacterium avium complex (MAC) infection. Disseminated MAC infection usually occurs in patients with CD4 cell counts less than 50/µL. Symptoms include fever, night sweats, weight loss, diarrhea, fatigue, and abdominal pain. Laboratory abnormalities often include evidence of bone marrow suppression and an elevated alkaline phosphatase level. The diagnosis is typically made by blood cultures (or cultures from other involved organs). Guidelines for the treatment of MAC in adults with HIV infection recommend clarithromycin as the preferred first agent and ethambutol as the second agent. On the basis of some evidence indicating improved survival and decreased emergence of drug resistance, some experts recommend the addition of rifabutin as a third agent. Primary prophylaxis for MAC prevention with azithromycin or clarithromycin is recommended for patients with HIV whose CD4 cell count is less than 50/µL.

Isoniazid, rifampin, and ethambutol are typically used to treat Mycobacterium kansasii, which most commonly causes a lung infection that mimics tuberculosis with cough, fever, weight loss, and cavitary lung disease.

Isoniazid and rifabutin are part of the 4- to 7-month continuation phase of treatment for active tuberculosis, which follows the initial 8-week treatment phase with rifabutin, isoniazid, pyrazinamide, and ethambutol. This patient does not have active tuberculosis.