09 Jan 2007

Picking the right Aids drug

Researchers report that they've developed a test that could give doctors a much clearer idea about which drugs to prescribe for patients infected with HIV.

Doctors already use a variety of tests to gauge whether the strains of HIV within a patient are immune to different types of Aids medications. But the developers of this new test say their version is much more sensitive and can detect smaller levels of resistance to drugs in the bloodstream.

While more research is needed and it will take at least two years for a new test to become widely available, the development will hopefully allow doctors "to make an informed selection of an HIV drug and delay resistance," said study author Dr Feng Gao, an associate professor at Duke University. "Patients can stay healthier for a longer time."

Over the past several years, drug resistance has become a larger problem for HIV patients. That's because, as time passes, the different strains of the Aids virus inside a person evolve into new forms and learn how to become immune to the effects of certain drugs.

Different in every person
"HIV is a different creature in every person," explained Rowena Johnston, vice president for research with the American Foundation for Aids Research. "Even within one individual body, there are many different types of HIV running around."

Drug resistance can even begin at the moment of infection if the person transmitting the virus is already immune to certain drugs as a result of treatment.

Enter the drug-resistance tests, which are designed to tell doctors which kinds of medications won't work in individual patients.

No magic bullet
"There's no magic bullet; there's no one-size-fits-all," Johnston said. "When you're going to treat HIV, you should start with three or more drugs. The question is, when you're picking from more than 20 drugs that are available, which are the good ones for this particular person?"

The problem is that the current tests aren't sensitive enough to catch all drug-resistant strains, meaning that even the best-designed drug regimen might not be as effective as it could be.

Researchers at Duke University tried out the new test on Aids patients and found that it detected drug resistance in strains that make up as little as .1 to .01 percent of virus in a person. According to the researchers, that's 1 000 times more sensitive than any existing test.

The researchers report their findings about the test in the February issue of Nature Methods, which was published online on Sunday.

According to a statement from Duke, the test's developers want to patent the technology and either create a company to develop it or license the test to another company.

Test may be expensive
There are some caveats. The test may be expensive, although Gao doesn't expect it to cost more than $1 000. Currently, according to Johnston, many patients don't get the best tests that are available, so there's a question about how many would get the new test.

Meanwhile, there's debate about how valuable it is to know that, for instance, 10 percent of a person's HIV strains are resistant to particular types of drugs.

"There's one school of people who says that if 10 percent of your virus population is resistant, that might not be that clinically important in the end," Johnston said. "Another school says that it might almost make the difference between life and death." – (HealthDayNews)