Clinical significance of drug resistance in human immunodeficiency virus.

Antiretroviral drugs exert only limited activity against viruses that replicate persistently to high levels. Thus, drug-resistant viruses readily emerge. It has been difficult to assess the contribution of such drug resistance to the failure of treatment with drugs that have only limited effectiveness in the first place. The emergence of zidovudine-resistant human immunodeficiency virus is predictive of clinical disease progression, although the relationship of this event to treatment failure is particularly complicated. The relationship between drug resistance and the loss of activity of non-nucleoside reverse transcriptase inhibitors and protease inhibitors appears to be more straightforward. The optimal use of antiretroviral drugs and combination regimens requires an appreciation of the impact of drug resistance.