As mentioned above, it is very difficult to prevent coming into contact with MAC organisms. In turn, most healthcare agencies, researchers, and HIV-treating physicians recommend that drugs to prevent MAC be used by patients with compromised immune systems. The risk of developing disease from MAC is greatest when a patient's T-cell count falls below 50. In turn, most experts recommend starting preventative therapy – called prophylaxis – when the T-cell count falls below 75.
As with the treatment of MAC, both clarithromycin and azithromycin are effective prophylaxis drugs. If either drug is taken correctly, the risk of developing MAC is decreased by approximately 70%. In other words, they are often effective, but not always. This can be a problem if MAC occurs while patients are taking either of these drugs. If MAC disease occurs during clarithromycin or azithromycin prophylaxis, it's possible that the organisms have developed resistance to the drugs. Because these drugs are the most effective compounds available to treat MAC, resistance will likely prevent either drug from being used as an effective therapy. What's more, MAC resistance to clarithromycin causes automatic cross-resistance to azithromycin, and vice versa.
Most experts believe that the benefits of prophylaxis using either clarithromycin or azithromycin outweigh the potential risks of drug resistance using these drugs.
Both azithromycin and clarithromycin cause similar side effects. To prevent MAC, clarithromycin must be taken once a day; azithromycin only needs to be taken once a week.
Before clarithromycin and azithromycin were studied in clinical trials, rifabutin (Mycobutin®) was the drug of choice to prevent MAC. However, it is not as effective as either clarithromycin or azithromycin and does not mix well with most anti-HIV medications.
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