The incidence of multidrug and full class resistance in HIV-1 infected patients is decreasing over time (2001–2006) in Portugal

In the last 2 decades, the management of HIV therapies has changed from the administration of one drug (monotherapy) to a combination of three or more antiretroviral drugs (HAART or Highly Active Anti-Retroviral Therapy). Currently, there are 24 single anti-HIV drugs approved by the FDA and new drugs are still getting developed. The potency of the current regimens is increasing and the drugs are getting better tolerated and easier to take. The mortality and morbidity of HIV infection has decreased in countries where therapy is available [1,2]. Changes in virologic response to initial combination antiretroviral therapy over calendar time indicate improvements in therapy [3], though it is too early to claim control of the infection on the long term. Therapy failure is due to such factors as lack of potency of the combination, insufficient drug adherence, and transmission of drug resistant virus [4], resulting in incomplete suppression of virus replication. Virus replication under drug selective pressure will invariably lead to increased drug resistance and cross-resistance, limiting further treatment options. Consequently, it is anticipated that drug resistance is and will continue to be a major issue in the effective treatment of HIV infection [5]. Especially, when HIV replication is not suppressed after exposure to several drug classes, multidrug resistance makes it difficult to optimize therapy and there is a higher incidence of AIDS and death [6,7]. Moreover, transmission of such multidrug resistant HIV is well documented [8], and is associated with suboptimal response to therapy [9], and (transmitted) resistance can persist over time [10,11].Therefore, there exists an eagerness to identify new anti-HIV drugs active against resistant viruses, though data that quantify the problem of multidrug resistance (MDR) are rather confusing. The results seem even contradictory due to different settings of the studies performed and the way of defining MDR. Literature about th