News Release

Many HIV+ urban indigents adhere well to strict anti-AIDS drug therapies; little drug resistance found among those who don't adhere

Peer-Reviewed Publication

University of California - San Francisco

Most HIV-positive people who are homeless or live in low-income hotels are able to stick to the demanding drug schedules required by combination anti-viral therapy, a preliminary study has found. The study, led by researchers at UC San Francisco and published in the March issue of the journal AIDS, focused on the "urban indigent" population, in which mental illness, alcoholism and drug addiction are common.

Thirty-eight percent of the people in the study - all on complex HIV therapy - took more than 90 percent of their medication, as measured by self-report, pill count and an electronic monitoring system -- an "impressive level of adherence for this population," the study's authors say. On average, the study subjects took 70 percent of their pills.

Contrary to expectations, the researchers also found that among those who failed to follow the drug regimen well, drug-resistance was rare. Many have argued that making the advanced AIDS therapies available to a wider population would lead to lower levels of adherence and a surge in drug-resistant virus as a result.

As expected, the study found a very close relationship between medication adherence and viral suppression. Levels of HIV found in the blood doubled with every 10 percent of pills the subjects missed - the equivalent of about two doses out of 21 a week.

"The finding that many homeless and marginally housed people adhere as well as others to the combination protease inhibitor therapy - and that very poor adherence may not generate drug-resistant virus - offers a new perspective for medical providers and public health officials concerned about prescribing to this high-risk population," said David R. Bangsberg, MD, MPH, assistant professor of medicine at UC San Francisco, director of the Epidemiology and Prevention Interventions (EPI) Center at San Francisco General Hospital Medical Center and lead author on the report in the journal AIDS.

"The common expectation has been that poor adherence would lead to drug resistance," said Andrew Moss, PhD, senior author of the study and professor of epidemiology and biostatistics at UCSF. "It may be that there is not enough circulating drug to select for resistance in poorly adherent people. Actually, the 'window of adherence' that selects for resistant virus may be much higher than many expect."

"We found that adherence predicted the level of virus suppression much better than tests for resistance did, and that near perfect adherence is essential to achieve undetectable levels of viral replication," Moss noted.

The scientists stressed that the findings of this small study -- 34 people followed for about two months - need to be confirmed in larger studies before firm conclusions can be drawn. The study drew participants from all homeless shelters and free meal programs in San Francisco, as well as from a random sample of low-cost, single-room occupancy hotels in the city. A total of 2,058 people were screened; 188 were identified as HIV positive from blood tests, and 36 of these people were found to be currently on protease inhibitor therapy. Of these, 34 agreed to participate in the study.

Participants were paid $10 for weekly visits where their drug adherence over the preceding three days was checked both by asking them to report their adherence, counting pills remaining from the previous supply, and by an electronically monitored pill container which allowed maximum reliability. People were followed for six to ten weeks.

In the AIDS paper, the researchers point out that the population of the "urban indigent" that they studied includes homeless, people with mental illness and those who inject illegal drugs. The researchers are now studying how these individual factors predict adherence to therapy.

"One of our goals now is to look specifically at these subgroups," Moss explains, "to determine if homelessness alone, or drug use, or mental illness predict particularly poor adherence to the drug regimen. Identifying the predictors of non-adherence will be essential to develop programs that improve adherence in this population."

The team acknowledges in the paper that the very act of studying adherence may well have increased it, and that the study looked at people for only a two-month period after they had been on therapy for about a year. Prospective studies will be necessary to confirm the findings, the scientists conclude.

Collaborators in the study with Moss and Bangsberg, and also co-authors on the AIDS paper, are Frederick M. Hecht, MD, assistant clinical professor of medicine, UCSF, AIDS program, San Francisco General Hospital Medical Center (SFGHMC); Edwin D. Charlebois, PhD, MPH, assistant professor of medicine, EPI Center, SFGMC, UCSF; Andrew Zolopa, MD, assistant professor of medicine, Stanford University School of Medicine; Mark Holodniy, MD, associate professor of medicine, also at Stanford and at AIDS Research Center, VA Palo Alto Health Care System; Lewis Sheiner, MD, professor of laboratory medicine, UCSF; Joshua D. Bamberger, MD, MPH, director of Urban Community Health, San Francisco Department of Public Health; and Margaret A. Chesney, PhD, professor of medicine and epidemiology and co-director of Center for AIDS Prevention Studies, UCSF.

The study was funded by the National Institute of Mental Health, the University Wide AIDS Research Program of the State of California, the AIDS Clinical Research Center of the University of California, the UCSF Gladstone Institute of Virology & Immunology Center for AIDS Research, and an unrestricted grant from Agouron.

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