Azithromycin Dosing for Disseminated MAC Infection

Core Treatment Regimen

The American Thoracic Society recommends azithromycin dosed at 500 mg orally once daily in combination with ethambutol 15 mg/kg daily for disseminated MAC infection, with consideration of adding rifabutin 300 mg daily as a third agent 1, 2, 3, 4
Azithromycin is an alternative to clarithromycin for disseminated MAC, though clarithromycin clears bacteremia more rapidly and is preferred when tolerated 1, 2, 3
The standard dosing for azithromycin is 500 mg orally once daily 1, 2, 3, 4
Ethambutol is dosed at 15 mg/kg orally once daily as a mandatory second agent 1, 2, 3, 4
Rifabutin is dosed at 300 mg orally once daily as an optional third agent, requiring dose adjustment with antiretrovirals 1, 2, 3, 4

Monotherapy is absolutely contraindicated, as nearly 50% of patients develop macrolide resistance when treated with a macrolide alone 1, 2, 3
Macrolides are the only agents for MAC where in vitro susceptibility correlates with clinical response 5
Baseline susceptibility testing should be performed, and macrolide-resistant strains require alternative regimens including aminoglycosides and quinolones 1, 2, 3, 4

The benefit of adding rifabutin as a third drug remains uncertain 1, 2, 3
At 300 mg/day, rifabutin shows no additional clinical benefit but reduced relapse with macrolide-resistant strains 1, 2, 3
At 450 mg/day, rifabutin shows modest clinical benefit observed 1, 2, 3
Rifabutin combined with clarithromycin causes significant drug interactions leading to arthralgias, uveitis, neutropenia, and hepatotoxicity 1, 2

Treatment should be lifelong unless immune reconstitution occurs with antiretroviral therapy 1, 2, 6
Discontinuation criteria include completion of ≥12 months of MAC treatment, being asymptomatic for MAC, and having a CD4 count >100 cells/μL sustained for ≥6 months on HAART 1, 2, 6
Restart treatment if CD4 count drops below 100 cells/μL 1, 2, 6

Never use clarithromycin doses above 500 mg twice daily, as higher doses are associated with excess mortality in AIDS patients 1, 2
Avoid clofazimine entirely, as it is associated with excess mortality in disseminated MAC 1, 2, 3, 4
Screen for QTc prolongation before initiating azithromycin, and contraindicate if QTc >450 ms (men) or >470 ms (women) 7, 8
Avoid aluminum/magnesium antacids, as they reduce azithromycin absorption when taken simultaneously 7, 9

For primary MAC prophylaxis in HIV patients with CD4 <50 cells/μL, azithromycin 1,200 mg once weekly is preferred over daily dosing due to lower resistance rates 6, 9

For macrolide-resistant strains, consider amikacin (aminoglycoside) and moxifloxacin (quinolone) 1, 2, 3, 4, 5
Cross-resistance exists between clarithromycin and azithromycin due to 23S rRNA gene mutations 10