Drug resistance in HIV-1

Purpose of the review Changing antiretroviral regimens and the introduction of new antiretroviral drugs have altered drug resistance patterns in human immunodeficiency virus type 1 (HIV-1). This review summarizes recent information on antiretroviral drug resistance. Recent findings As tenofovir and abacavir have replaced zidovudine and stavudine in antiretroviral regimens, thymidine analog resistance mutations have become less common in patients failing antiretroviral therapy in developed countries. Similarly, the near universal use of ritonavir-boosted protease inhibitors (PI) in place of unboosted Pis has made the selection of PI resistance mutations uncommon in patients failing a first-line or second-line PI regimen. The challenge of treating patients with multidrug-resistant HIV-1 has largely been addressed by the advent of newer Pis, second-generation non-nucleoside reverse transcriptase inhibitors and drugs in novel classes, including integrase inhibitors and CCR5 antagonists. Resistance to these newer agents can emerge, however, resulting in the appearance of novel drug resistance mutations in the HIV-1 polymerase, integrase and envelope genes. Summary New drugs make possible the effective treatment of multidrug-resistant HIV-1, but the activity of these drugs may be limited by the appearance of novel drug resistance mutations.