From the Guidelines
HIV patients should receive prophylaxis against Mycobacterium avium complex (MAC) when their CD4 count falls below 50 cells/mm³. The recommended first-line prophylactic medication is azithromycin 1200 mg once weekly or clarithromycin 500 mg twice daily, as supported by the most recent guidelines 1. An alternative option is rifabutin 300 mg daily (with dose adjustment for patients on certain antiretrovirals). Prophylaxis can be discontinued if the patient's CD4 count increases to above 100 cells/mm³ for at least 3 months in response to antiretroviral therapy.
Key considerations for MAC prophylaxis include:
- The risk of MAC infection increases substantially when CD4 counts drop below 50 cells/mm³, which is why this threshold is used to initiate prophylaxis 1.
- Primary prophylaxis against MAC has been shown to reduce the incidence of disseminated MAC disease by approximately 50% in patients with advanced HIV.
- Azithromycin and clarithromycin also confer protection against respiratory bacterial infections, adding to their benefit as first-line prophylactic agents 1.
- Before initiating prophylaxis, it is essential to rule out disseminated MAC disease through clinical assessment, which may include obtaining a blood culture for MAC if warranted, and to exclude active tuberculosis to prevent rifampin resistance 1.
Overall, the initiation of MAC prophylaxis at a CD4 count below 50 cells/mm³ is a critical component of comprehensive care for HIV-infected patients, aiming to prevent the morbidity and mortality associated with disseminated MAC disease.
From the FDA Drug Label
CLINICAL STUDIES Two randomized, double-blind clinical trials (Study 023 and Study 027) compared rifabutin (300 mg/day) to placebo in patients with CDC-defined AIDS and CD4 counts ≤200 cells/µL. Most cases of MAC bacteremia (approximately 90% in these studies) occurred among participants whose CD4 count at study entry was ≤100 cells/µL. The median and mean CD4 counts at onset of MAC bacteremia were 13 cells/µL and 24 cells/µL, respectively. These studies did not investigate the optimal time to begin MAC prophylaxis
The CD4 count at which an HIV patient gets MAC prophylaxis is ≤200 cells/µL, but most cases of MAC bacteremia occurred at CD4 counts ≤100 cells/µL. The optimal time to begin MAC prophylaxis was not investigated in these studies 2.
- Key points:
- CD4 count ≤200 cells/µL for MAC prophylaxis
- Most MAC bacteremia cases occurred at CD4 counts ≤100 cells/µL
- Optimal time to begin MAC prophylaxis not investigated 2
From the Research
CD4 Count and MAC Prophylaxis
- The CD4 count at which an HIV patient should receive MAC prophylaxis is generally considered to be less than 50 cells/mL, as stated in studies 3, 4, 5.
- This recommendation is based on the fact that the incidence of MAC infection increases linearly over time as the CD4+ cell count approaches zero, and that a large majority of MAC infections occur in patients with CD4+ cell counts below 50/microliter 4.
- However, some studies suggest that routine MAC prophylaxis may not be necessary in the era of effective antiretroviral therapy (ART), especially for patients who respond well to treatment and have a stable CD4+ cell count above 100 cells/microL 6, 7.
- The decision to provide MAC prophylaxis should be individualized, taking into account factors such as the patient's response to antiretroviral treatment, CD4+ cell count, and history of AIDS-defining opportunistic events 4, 7.
Guidelines for MAC Prophylaxis
- The US Public Health Service and the Infectious Diseases Society of America recommend prophylaxis against MAC for HIV-infected patients with a CD4+ cell count less than 50 cells/mm3 3, 5.
- The recommended prophylactic regimen includes azithromycin or clarithromycin, with or without rifabutin 3, 5.
- Prophylaxis can be discontinued in patients who have responded to HAART and have a stable CD4+ cell count above 100 cells/microL 7.