Fact Sheet: Mycobacterium Avium Complex(MAC)

Mycobacterium avium complex, or MAC, is a serious bacterial infection that HIV positive people can get. MAC is related to tuberculosis. MAC is also sometimes called MAI, which stands for Mycobacterium avium intracellulare.

MAC infection is usually found only in people with under 50 T4 cells. The symptoms of MAC can include weight loss, fevers, chills, night sweats, swollen glands, abdominal pains, diarrhea, and overall weakness. MAC usually affects the intestines and inner organs first, causing liver tests to be high. Swelling and inflammation also occur.

Preventing MAC: A multi-center trial has shown that rifabutin, or Mycobutin, can nearly cut in half the rate at which people develop MAC. The drug is approved for prevention of MAC. Recent information from studies of rifabutin show that the drug may also help people live longer. Taking the drug for MAC prevention reduced the risk of dying by 14% in these studies. The most serious side effects of rifabutin are low white blood-cell counts and elevated liver enzymes. Very few people in trials had to discontinue the drug because of toxicity.

Clarithromycin (Biaxin) is the second drug to be approved for the prevention of MAC. In studies, it reduced the number of MAC infections by 69%, or over two-thirds. In a recent study people taking this drug to prevent MAC lived longer on average than those receiving placebo (a fake or dummy pill used in clinical trials to see if a treatment really works).

A third drug called azithromycin has now also been approved for preventing MAC. This drug can be taken once a week. A recent study found that azithromycin was better at preventing MAC than rifabutin. Azithromycin has not been directly compared to clarithromycin for preventing MAC.

A recent study comparing rifabutin, clarithromycin and a combination of the two drugs found clarithromycin to be clearly superior to rifabutin for the prevention of MAC.

However, clarithromycin is also though to be the most effective treatment for MAC. Some doctors are concerned that if a person develops MAC while taking clarithromycin, the MAC infection will be resistant to the effects of the drug. This would make the infection much harder to treat. In studies, half the people that developed MAC while taking clarithromycin turned out to have MAC infections that were resistant to the drug. This might have been due to their having an undetected MAC infection before starting preventive treatment. It is very important that you are properly tested for both active MAC and tuberculosis (TB) infection before starting any preventive treatment.

Treating MAC: The recommendations of the US Public Health Task Force on MAC are that treatment for disseminated MAC should include at least 2 drugs, one of which should be clarithromycin or azithromycin. Effect treatment should continue for life.

The Task Force also noted that many doctors use ethambutol as the second drug, and that other second, third or fourth drugs(s) include: rifabutin, rifampin, ciprofloxacin and amikacin. Due to a recent study, clofazimine (trade name Lamprene) is no longer recommended as a part of MAC treatment. The study found that poor survival was associated with adding clofazimine to MAC treatment. The recommendations do not support the use of isoniazid (INH) or pyrazinamide for MAC therapy.

A recent alert from the National Institutes of Health also notes that the drug clarithromycin (Biaxin) should never be used at dose higher than the approved dose of 500mg twice a day.

Some cautions: If you're taking AZT, rifabutin can reduce the amount of AZT in your blood. Lower amounts of AZT would make the AZT less effective against HIV. Rifabutin also lowers the amount of clarithromycin in the blood.

The anti-fungal drug fluconazole (Diflucan) can increase the amount of rifabutin in the blood by up to 80%. Increased levels of drug in the blood may lead to greater risk of side effects.

Side effects of rifabutin can be kidney and liver damage, bone marrow suppression, rash, fever, gastrointestinal distress, and uveitis (a swelling of the eye). Early warning signs of kidney problems are decrease urination, increased thirst, or light-headedness after you stand up. Uveitis can cause eye pain, light sensitivity, redness and blurred vision. A harmless side effect or rifabutin can be an orange color that appears in the urine and other body fluids, and sometimes on the skin, too. Soft contact lenses can become permanently discolored. Side effects of clarithromycin can be diarrhea, nausea, and abnormal or metallic taste. Side effects of azithromycin include mild GI symptoms, such as nausea and diarrhea, dizziness, sensitivity to sunlight, and rare cases of hearing loss.