Wednesday, January 04, 2006
Mycobacterium Avium Complex (MAC)
Mycobacterium Avium Complex (MAC) is a serious illness caused by common bacteria. MAC is also known as MAI (Mycobacterium Avium Intracellulare). MAC infection can be localized (limited to one part of your body) or disseminated (spread through your whole body, sometimes called DMAC). MAC infection often occurs in the lungs, intestines, bone marrow, liver and spleen.
The bacteria that cause MAC are very common. They are found in water, soil, dust and food. Almost everyone has them in their body. A healthy immune system will control MAC, but people with weakened immune systems can develop MAC disease.Up to 50% of people with AIDS may develop MAC, especially if their CD4 cell count is below 50. MAC almost never causes disease in people with more than 100 CD4 cells.HOW DO I KNOW IF I HAVE MAC?
The symptoms of MAC can include high fevers, chills, diarrhea, weight loss, stomach aches, fatigue, and anemia (low numbers of red blood cells). When MAC spreads in the body, it can cause blood infections, hepatitis, pneumonia, and other serious problems.
Many different opportunistic infections can cause these symptoms. Therefore, your doctor will probably check your blood, urine, or saliva to look for the bacteria that causes MAC. The sample will be tested to see what bacteria are growing in it. This process, called culturing, can take several weeks. Even if you are infected with MAC, it can be hard to find the MAC bacteria.If your CD4 cell count is less than 50, your doctor might treat you for MAC, even without a definite diagnosis. This is because MAC infection is very common but can be difficult to diagnose.
HOW IS MAC TREATED?
The MAC bacteria can mutate and develop resistance to some of the drugs used to fight it. Doctors use a combination of antibacterial drugs (antibiotics) to treat MAC. At least two drugs are used: usually azithromycin or clarithromycin plus up to three other drugs. MAC treatment must continue for life, or else the disease will return.
People react differently to anti-MAC drugs. You and your doctor may have to try different combinations before you find one that works for you with the fewest side effects.
The most common MAC drugs and their side effects are:
Amikacin (Amkin®): kidney and ear problems; taken as an injection.
Azithromycin (Zithromax®): nausea, headaches, vomiting, diarrhea; taken as capsules or intravenously.
Ciprofloxacin (Cipro® or Ciloxan®): nausea, vomiting, diarrhea; taken as tablets or intravenously.
Clarithromycin (Biaxin®): nausea, headaches, vomiting, diarrhea; taken as capsules or intravenously. Note: The maximum dose of Biaxin is 500 milligrams twice a day.
Ethambutol (Myambutol®): nausea, vomiting, vision problems.
Rifabutin (Mycobutin®): rashes, nausea, anemia. Many drug interactions.
Rifampin (Rifampicin®, Rifadin®, Rimactane®): fever, chills, muscle or bone pain; can turn urine, sweat, and saliva red-orange (may stain contact lenses); can interfere with birth control pills. Many drug interactions.
CAN MAC BE PREVENTED?
The bacteria that cause MAC are very common. It is not possible to avoid being exposed. The best way to prevent MAC is to take strong anti-HIV medications. Even if your CD4 cell count drops very low, there are drugs that can stop MAC disease from developing in up to 50% of people.
The antibiotic drugs azithromycin and clarithromycin have been used to prevent MAC. These drugs are usually prescribed for people with less than 75 CD4 cells.Combination antiretroviral therapy can make your CD4 cell count go up. If it goes over 100 and stays there for 3 months, it may be safe to stop taking medications to prevent MAC. Be sure to talk with your doctor before you stop taking any of your prescribed medications.
DRUG INTERACTION PROBLEMS
Several of the drugs used to treat MAC interact with many other drugs, including antiretroviral drugs, antifungal drugs, and birth control pills. This is especially true for rifampin, rifabutin and rifapentine. Be sure your doctor knows about all the medications that you are taking so that all possible interactions can be considered.
THE BOTTOM LINE
MAC is a serious disease caused by common bacteria. MAC can cause serious weight loss, diarrhea, and other symptoms.
If you develop MAC, you will probably be treated with azithromycin or clarithromycin plus one to three other antibiotics. You will have to continue taking these drugs for life to avoid a recurrence of MAC.People with 75 CD4 cells or less should talk with their doctors about taking drugs to prevent MAC.
Mycobacterium avium complex
Mycobacterium avium complex, or MAC, is a serious bacterial infection that HIV+ 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 thought 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 active 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. Effective 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 drug(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 500 mg 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 decreased 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 of 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. Clarithromycin may cause severe abdominal pain at high doses. Side effects of azithromycin include mild GI symptoms such as nausea and diarrhea, dizziness, sensitivity to sunlight, and rare cases of hearing loss.