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National Institute of Allergy and
Infectious Diseases (NIAID)

Wednesday, July 10, 1996
11:30 a.m. Pacific Time (2:30 p.m. Eastern Time)

Media Contact:
John Bowersox
(301) 402-1663

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NIAID Study Rules Out High-Dose Clarithromycin for AIDS-Related MAC

Treatment regimens for Mycobacterium avium intracellular complex (MAC), a life-threatening infection common among people with late-stage AIDS, should include not more than a 500 milligram (mg), twice-daily dose of clarithromycin, according to an ongoing study supported by the National Institute of Allergy and Infectious Diseases (NIAID). A higher dose was associated with lower survival rates among study participants. The finding will be presented today at the XIth International Conference on AIDS in Vancouver, British Columbia.

"All physicians who care for patients with HIV disease and AIDS should take note of this very important finding," says Jack Killen, M.D., director of NIAID's Division of AIDS. "Although the lower dose, given twice a day in combination with other drugs, is the standard of care in general practice, some studies had suggested that a higher dose might be more effective."

In the multicenter NIAID clinical trial comparing multidrug treatment regimens for people with MAC, researchers used regimens that included clarithromycin in twice-daily doses of either the standard dose of 500 mg or a higher dose of 1000 mg. Previous studies showed that higher doses kill MAC bacteria in AIDS patients' blood more quickly and thus might have greater clinical efficacy, explains study chair David L. Cohn, M.D., of the Denver Public Health Department and the University of Colorado Health Sciences Center, also in Denver.

"Somewhat paradoxically, however, when we looked at patient survival early in the study, we saw an opposite effect," says Dr. Cohn.

An interim analysis conducted several months after the study began indicated that 43 percent of the patients on the 1000 mg dose of the drug had died, compared with 22 percent of the patients receiving the 500 mg dose. The researchers immediately discontinued the clarithromycin dose comparison and began giving all patients in the study the 500 mg, twice-daily dose.

"The data suggest that the higher dose is associated with higher mortality, but we can't explain why this happens," says Dr. Cohn.

"It is important to remember that clarithromycin remains the most potent drug for the treatment of disseminated MAC infection and that 500 mg, twice daily in combination with other antibiotics, is the standard of care," says Dr. Cohn. Treatment often results in improvement in symptoms and clearing of bacteria from the blood. However, relapse may occur several months after treatment.

All patients in the ongoing study, conducted through the NIAID's Terry Beirn Community Programs for Clinical Research on AIDS (CPCRA), receive a three-drug regimen that includes clarithromycin, ethambutol, and either rifabutin or clofazamine. The study will be completed later this year, and researchers hope to determine what combination of these drugs produces the fewest side effects in people with MAC.

The CPCRA is a network of primary care physicians and nurses who work with NIAID staff to design and conduct community-based clinical trials in patients with HIV disease and AIDS. NIAID currently funds 16 CPCRA units in 15 cities throughout the United States.

NIAID conducts and supports research—at NIH, throughout the United States, and worldwide—to study the causes of infectious and immune-mediated diseases, and to develop better means of preventing, diagnosing and treating these illnesses. News releases, fact sheets and other NIAID-related materials are available on the NIAID Web site at

About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit

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NIAID Archive

Important note: Information on this page was accurate at the time of publication. This page is no longer being updated.

Last Updated July 10, 1996