Much of the conference in Glasgow has concentrated on new antiretroviral agents that have activity against multidrug-resistant (MDR) virus. It is clear that the prevalence of MDR HIV has increased as patients have gained more exposure to multiple classes of drug. However, one can get a better picture of MDR virus trends over time by examining the incidence, or new occurrence, of MDR HIV on a year-by-year basis.

A study presented by Belgian researchers, led by Jurgen Vercauteren of the Rega Institute, was designed to examine trends in the incidence of MDR HIV based on data from 2,373 Portuguese patients.¹ The resistance database used in the analysis covers 22 hospitals in Portugal and contains 3,039 viral isolates that were examined for resistance between July 2001 and June 2006. One genotypic resistance test per patient per year was included in the analysis, and MDR HIV was defined as virus that remained susceptible to at most one active drug. Results were examined using a Poisson regression model that was corrected for confounding by multivariate regression. The drugs enfuvirtide (T-20, Fuzeon), tipranavir (TPV, Aptivus) and TMC114 (darunavir, Prezista) were not considered as potentially active drugs for this analysis, as these drugs were not available at all time points of the study.

The results showed a striking reduction in the incidence of MDR HIV over time, with an odds ratio of 0.80. In essence, this means that the odds of the presence of new drug resistance are reduced by 20% each year.

The authors of this study concluded that the reduction in MDR HIV incidence reflects increasing highly active antiretroviral therapy (HAART) efficacy. In other words, as the drugs for HIV have improved, the chance that patients will experience treatment failure due to the emergence of new resistance has decreased. They also concluded that the development of new drugs with activity against resistant virus may become less important as the incidence of MDR HIV wanes. Instead, the emphasis may shift toward developing drugs with improved tolerability, ease of use and reduced toxicity.

So what does this study add to our understanding? It is good to see that the MDR HIV incidence is decreasing, although it would be useful to compare the Portuguese data with data from other cohorts. MDR HIV remains an important clinical problem, and there are a significant number of individuals who need, and who will continue to need, new drugs. It is reassuring to know that as HIV drugs have continued to improve, patients who are currently entering into HIV treatment may be less likely to develop MDR virus in the future.

Footnote

1. Vercauteren J, Theys K, Debruyne M, Carvalho AP, Vandamme AM, Camacho R. Declining incidence of multidrug-resistant HIV-1 over time (2001-2006): which new drugs do we really need? In: Program and abstracts of the 8th International Congress on Drug Therapy in HIV Infection; November 12-16, 2006; Glasgow, United Kingdom. Abstract PL5.5.