What is multi-class drug resistance (MDR)?
Multi-class drug resistance (MDR) is defined as high level drug resistance in more than one antiretroviral drug class. The three classes which are routinely evaluated for resistance are protease inhibitors (PI), nucleoside reverse transcriptase inhibitors (NRTI) and non-nucleoside reverse transcriptase inhibitors (NNRTI). MDR does not necessarily accelerate disease progression, but high level resistance to more than one drug class may lead to reduced treatment options that can be expensive and difficult to maintain.