Important note: Information in this article was accurate in 1996. The state of the art may have changed since the publication date.

Reuters NewMedia, Inc. - Friday, 25 October 1996
David Morgan

The U.S. Centers for Disease Control and Prevention (CDC), seeking to lead doctors through the wilderness of new AIDS therapies, issued its first set of guidelines for treating AIDS patients who suffer from TB with protease inhibitors.

"It's a very new thing," said Dr. Jonathan Kaplan, a CDC expert on opportunistic infections. "These are quite serious drug interactions and you really have to think about what you're going to do."

The drug "cocktail" recently has proved effective in suppressing the HIV virus that causes AIDS. But because they have been on the market for less than a year, scientists are only now coming to grips with the drugs' curative potentials as well as their limitations.

The new class of drugs includes Abbott Laboratories' Novir (ritonavir), Hoffman La Roche's Invirase (saquinavir) and Merck's Crixivan (indinavir). A fourth, Agouron Pharmaceuticals' Viracept (nelfinavir) is expected to be available soon.

The CDC described all four drugs as "the most potent antiretroviral agents available to treat patients with HIV disease."

But when protease inhibitors are used alongside rifamycin derivatives, which combat mycobacterial infections including TB, problems quickly develop in both treatment regimens.

"Rifamycins accelerate the metabolism of protease inhibitors, resulting in subtherapeutic levels of the protease inhibitors," the federal agency said in its weekly report on health issues.

"In addition, protease inhibitors retard the metabolism of rifamycins, resulting in increased serum levels of rifamycins and the likelhood of drug toxicity."

Rifamycins include the anti-bacterial drugs rifabutin and rifampin, the latter being viewed as an essential component in combatting TB.

There are no accurate figures on TB incidence among AIDS sufferers. Federal government data show that about 3 percent of new AIDS cases reported in 1995 involved TB infection. But that does not include patients who went on to contract TB after being diagnosed with AIDS.

Kaplan said the problems of mixing the two classes of drugs can be especially difficult because the onset of TB and perceived need for treatment with protease inhibitors often occur near the same advanced stages of AIDS.

The CDC recommends that protease inhibitors be withheld from patients receiving treatment for TB, because TB can more quickly become life-threatening. But the agency suggests it would be possible to use both the protease inhibitors and anti-TB rifamycins if doses can be modified to compensate for drug interaction.
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