Step Perspective, Volume 5, Number 1; A Publication Of The Seattle Treatment Education Project - February 1993 Jeff Schouten, MD
Mycobacterium avium complex (MAC) is a serious life- threatening infection in persons with severely weakened immune systems. MAC was formerly referred to as Mycobacterium avium intracellulare (MAI). The causative agent is a mycobacterium like tuberculosis, which causes disseminated infections. Clinical symptoms usually include fever, weight loss and other nonspecific infectious symptoms. The clinical pattern depends on the organ systems most infected, and usually includes the gastrointestinal tract, liver, and blood. Persons with CD4 counts less than 250 mm3 are at risk, with the risk greatly increasing when CD4 counts are less than 50 mm3. One study followed 1020 people with AIDS or ARC for a medial of 600 days with CD4 counts less than 250 mm3 who were receiving AZT found that 19% developed MAC. A mycobacterium avium can often be found in stool cultures in asymptomatic persons, but this usually is not an indication for therapy. Treatment for MAC is usually based on finding the organism in blood cultures. Cultures can take three to six weeks for results since the organism is very slow growing in lab cultures. Treatment of MAC, once the infection is clinically significant, is difficult. Treatment usually consists of multiple antibiotic combinations, with serious side-effects. Clarithromycin is the drug used in most combinations. Therefore, the need is great for effective prophylactic therapy. For most HIV-infected people, now that there is very effective prophylaxis for Pneumocystis carinii pneumonia, MAC is the most common life- threatening infection. The FDA has recently approved the use of rifabutin for the prophylaxis of MAC. Rifabutin (300mg) was approved for use for MAC prophylaxis in HIV positive patients 12 years of age or older with CD counts of 200 mm3 or below. Rifabutin is the first drug for which controlled data is available to show efficacy against MAC. Rifabutin use in patients with established MAC has not been shown to be effective. The most common side effects, which tend to be minor, include flu-like symptoms, gastrointestinal problems, rash, and discoloration of the urine. The other reported less common side effects of rifabutin include, neutropenia (lowering of white blood cell count), anemia, lowering of platelets, and mild liver and kidney damage. These side effects are usually asymptomatic and reversible if the dug is discontinued. Rifabutin is not 100% effective in preventing MAC, but it did prevent MAC infection in a significant group of those treated. Two studies were reported at the 1992 International AIDS Conference which noted the efficacy of rifabutin prophylaxis for MAC. William Cameron, M.D. compared rifabutin (300mg a day) to placebo in 566 people with AIDS with CD4 counts less than 200 mm3. Fifty people in the placebo group developed MAC compared to only 24 in the rifabutin treated group. Fred Gordin, M.D. reported another rifabutin prophylaxis study and observed that 15% of the people in the placebo group developed MAC, compared to only 9% in the rifabutin group. Tosina Claridy, who spoke at the STEP Community Forum on October 24, 1992, emphasized the importance of tuberculosis (TB) testing in all persons who are considering rifabutin for MAC prophylaxis. This is important since rifabutin is closely related to a drug which has some efficacy against TB, rifampin, but only when used in combination therapy. Rifabutin therapy, in someone with TB, could result in the development of a drug- resistant strain of TB.
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Always watch for outdated information. This article first appeard in 1993. This material is designed to support, not replace, the relationship that exists between you and your doctor.
This information is designed to support, not replace, the relationship that exists between you and your doctor.