Sequencing of therapy to avoid resistance and the need for new antiretroviral drugs in the treatment of HIV disease.

HIV-1 drug regimens now offer more potent, less toxic and more durable choices. However, strategies addressing convenient sequential use of active antiretroviral combinations are rarely presented in the literature. Studies have seldom directly addressed this issue, despite it being a matter of daily use in clinical practice. This is, in part, because of the complexity of HIV-1 resistance information. Nevertheless, several principles can effectively assist the planning of antiretroviral drug sequencing. The introduction of tenofovir, abacavir and emtricitabine into current nucleoside backbone options, with each of them selecting for an individual pattern of resistance mutations, now permits sequencing in the context of previously popular thymidine analogs (zidovudine and stavudine). Similarly, newer ritonavir-boosted protease inhibitors could be potentially sequenced in a manner that uses the least cross-resistance prone PI at the start of therapy while leaving the most cross-resistance prone drugs for later, as long as there is rationale to employ such a compound because of its utility against commonly observed drug-resistant forms of the virus. The ability to sequence new therapies will be enhanced by availability of new antiretroviral drugs.