Measuring levels of anti-HIV drugs in hair samples rather than in the blood can better predict whether they will be effective or not, U.S. investigators report in the journal AIDS.

Blood levels of these antiretroviral drugs “have such a dismal record in terms of predicting HIV treatment outcomes,” lead author Dr. Monica Gandhi at the University of California, San Francisco, told Reuters Health. Blood levels may not reflect how well the patient is adhering to treatment, she explained, and factors such as diet and interacting medications can cause variability.

Hair samples, on the other hand, reflect drug exposure over time, she continued. “Therefore, we started collecting hair specimens from the patients in our cohort almost 4 years ago in anticipation of developing methods to analyze antiretrovirals in hair and examining the association of these levels with treatment outcomes.”

In the current study, the researchers measured drug levels in hair from 224 women who were starting a new antiretroviral regimen. Sampling required 10-20 hair strands, clipped close to the scalp.

As hair levels of the drugs increased, so did the likelihood that HIV levels were successfully reduced, the report indicates.

If hair drug levels are high, but HIV levels continue to rise, it suggests that the virus may have become resistant to the antiretroviral agents being used, Gandhi said. If hair drug levels fall and HIV levels increase, it suggests that either the patient is not adhering with treatment or is using a new drug that is reducing the absorption of the antiretroviral drug.

Gandhi’s group now plans to examine the relationship between drug levels in hair and side effects on the antiretroviral drugs.

The purpose would be to see if some patients can lower their dose of antiretroviral drugs to reduce rate of side effects, while still having a treatment response, the investigator explained.

“We also plan to test this method in resource-limited settings, such as in India or Africa, where blood collection and (HIV) monitoring may be expensive and difficult.”

SOURCE: AIDS, February 20, 2009.