Development of antiretroviral drug resistance.

fers among HIV variants. Indeed, we have limited knowledge of resistance muta tions in non-B subtypes of HIV type 1 (HIV-1) and their clinical relevance, despite the fact that more than 90% of patients with HIV-1 infection worldwide have non– subtype B variants of HIV-1. Most reports on drug resistance deal with subtype B infections in developed countries. Both enzymatic and virologic data indicate that naturally occurring polymorphisms among different HIV subtypes can influence HIV-1 susceptibility to individual antiretroviral drugs and the propensity of HIV to acquire certain resistance mutations. Furthermore, resistance pathways in different subtypes may affect drug cross-resistance and the potential use of specific secondline regimens. This concern may be increased in developing countries. Substantial natural genetic variation has led to the subclassification of HIV-1 group M (major) into nine subtypes (A through D, F through H, and J and K) and nu