United Press International
Ed Susman

Sally Blower, associate professor of medicine, microbiology and immunology at the University of California, San Francisco, said that as more people are treated with drugs such as protease inhibitors, the greater the likelihood that drug resistance will occur. She said drug resistance will lead to treatment failures, and that would eventually translate into a 20 percent increase in new HIV infections after 10 years.

Blower said her mathematical model of how HIV-infection would affect the San Francisco gay population shows that if patients could be treated optimally with the drug combinations, there could be a 20 percent decrease in infections.

But she said, a more likely prediction is that the drug usage will fail patients for a number of reasons. Blower said the more pessimistic outcome -- known in mathematical lingo as "amplified perversity" -- can develop due to several factors:

--Patients will fail to comply with complicated regimens. In some cases patients have to take handfuls of pills at various times of the day. Blower said, "Pharmaceutical companies are trying to develop combinations of pills to reduce the numbers that one has to take a day to reduce problems of compliance."

--Some patients will be biologically incompatible with the regimens.

"There are going to be some people in which the therapy just won't work," said Blower, cautioning that failure of the medicine shouldn't be blamed on the patient.

--Doctors will prescribe inappropriate or wrong dosages.

--Treatment interruptions can be caused by communication lapses among various segments of the health care system.

In highly-active anti-retroviral therapy (HAART), which is the current mainstay of anti-HIV treatment, the ability of the virus to mutate into a resistant form is inhibited by drugs. If that drug treatment is interrupted or fails to suppress the mutation process, the virus can rebound rapidly and can be far more difficult to treat. And that new, resistant mutation can be transmitted to others.

"This type of transmission has already occurred," said David Baltimore, an AIDS vaccine specialist and president of the California Institute of Technology.

"The problems Dr. Blower cites are reasons why we have to keep trying to develop new drugs, ," Baltimore said today at a press briefing at the annual meeting of the American Association for the Advancement of Science in Anaheim, Calif. "Most of the drugs we use now, the virus can mutate around," he said.

Blower said the answer is not to withhold treatment, but to emphasize compliance and to encourage patients to change risky sexual practices. "A 50 percent reduction in risky sexual practices," she said, "will reduce new HIV infections by as much as 40 percent over 10 years."

Blower's model suggests that as treatment of HIV infection increases from its present 10 percent of affected persons to 90 percent, the level of new infections will rise or fall depending upon how strictly patients can be kept on treatment regimens.
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