Prevalence of Drug Resistance High

The issue of drug resistance has been an important concern in the area of HIV/AIDS treatment for several years. Over time, HIV is able to alter its structure in a way that allows it to resist the effects of antiretroviral drugs. When resistance develops, the effect of these drugs becomes weaker and patients can experience surges in their viral load. One major cause of drug resistance is a patient's inability to follow his or her drug schedule as prescribed. When doses of HIV medications are missed, the virus has an opportunity to escape the drugs' control and to develop resistance. According to a study presented this week in Spain, drug resistance seems to be occurring at alarmingly high levels.

Dr. Brendan Larder and colleagues in Cambridge, England, presented results from a resistance study involving almost 12,000 HIV samples at the fourth International Workshop on HIV Drug Resistance and Treatment Strategies. After testing for genotypic resistance, the researchers found that only 21.8% of the samples were sensitive to all three classes of antiretroviral drugs. They also discovered that as many as one quarter of the samples contained virus that was resistant to all three drug classes.

The high prevalence of drug resistant strains of HIV in this large group of patients raises questions about the need for pretherapy resistance testing. Indeed, according to Dr Larder, these findings "make it compelling to know what the status of the virus is before a physician changes or adjusts therapy in patients."

Have No Doubt: Resistance Transmits

Disturbing numbers have also emerged from a study involving recently infected but untreated HIV-postive subjects. The study, which was published in the May 26 issue of AIDS, was conducted on 114 military personnel who had been infected with HIV for no more than three years and who had never received antiretroviral treatment.

Both genotypic and phenotypic resistance were assessed. The researchers reported a "higher than expected frequency" of drug resistance in these subjects. Resistance to non-nucleoside reverse transcriptase inhibitors (nevirapine, delavirdine, efavirenz) was most common, although resistance to both nucleoside analogues and protease inhibitors was also detected. In view of these results, the researchers suggest that "primary resistance to antiretroviral drugs could pose a substantial problem in the initial clinical management of HIV-1 infected patients." They also stress that the role and potential clinical benefit of pretherapy resistance testing needs to be determined.

AIDS 2000;14:1009-15.

From Canadian AIDS Treatment Information Exchange (CATIE). For more information visit CATIE's Information Network at http://www.catie.ca.