Drug adherence among homeless may be good
Drug adherence among homeless may be good
Research finds low resistance rate in non-compliers
Researchers in San Francisco who studied HIV-positive people who were homeless or lived in marginal housing found that more than one-third of them were doing a very good job of complying with their drug regimens.
"Many people who are homeless or marginally housed are able to adhere quite well," says David Bangsberg, MD, MPH, assistant professor of medicine at the University of California in San Francisco and at San Francisco General Hospital. Bangsberg was a key investigator in the study.
"Thirty-eight percent of the people in the study were taking more than 90% of the medications by our unannounced poll count measure, which is a conservative measure of adherence," Bangsberg says. "This is a population where drug use and mental illness are common, in addition to the simple stresses of living on the street."
Investigators spent two months measuring adherence among 34 HIV-positive people. The methods they used were:
• finding the participants on a random day during daylight hours and counting their pills;
• using pill bottles with an electronic microchip that records each time the pill bottle is opened and closed;
• asking participants about their medication use.
Adherence and viral load matched
Researchers found that each of the independent measures of adherence was very closely associated with patients’ viral load at the time the adherence measures were obtained, Bangsberg adds.
The study looked at adherence as a continuous variable between 0% and 100% and compared this with a viral load between 0% and a maximum number that was assigned 100%. "We found that our measures of adherence explained up to 67% of the variation in viral load between individuals, and that’s highly significant," Bangsberg explains.
Another key finding in the study was that genotypic resistance testing did not independently explain the participants’ variation in viral load, once it was controlled for adherence, Bangsberg says. While the viral load would go down when adherence increased, this did not result in a similar decrease in viral resistance.
"Adherence was a much better explanation for virologic failure than genotypic resistance," Bangsberg says. "Even people with resistant virus had low levels of viral replication with resistance if they were taking their medications."
Bangsberg says one of the more interesting research findings was that HIV-infected people who had very poor adherence, taking less than 50% of their prescribed medications in a year’s time, had no resistance to protease inhibitors. Resistance developed among the people who were adhering better to their medication regimens, even if their viral loads were decreasing.
These types of findings have important public policy implications, Bangsberg says.
"Many people withhold antiretroviral therapy from an indigent population because of the expectation of very poor adherence and the belief that less than 50% adherence will likely lead to drug resistance," Bangsberg says. "Our data didn’t support that expectation, and we believe there probably is not enough drug pressure with less than 50% adherence to select resistance."
The non-adhering HIV-infected people had high viral loads with a wild-type virus, but no protease inhibitor resistance.
While giving the antiretrovirals to a homeless population does not help those people who do not adhere to their medications, it also does not create a public health threat, and more than one-third of those individuals may adhere very well and be helped by the drugs, Bangsberg says.
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