How Common Is Drug Resistance?
The prevalence of ART drug resistance has changed over time. Early in the epidemic, patients treated with zidovudine (AZT) or stavudine (d4T) mono-therapy quickly developed resistance to these drugs. Likewise, dual nucleoside reverse transcriptase inhibitor (NRTI) regimens used in the early 1990s also led to NRTI drug resistance, albeit at a slightly slower rate compared with mono-therapy. With the advent of protease inhibitors and use of triple combination therapy, profound reductions in HIV viremia were achieved. However, treatment failure rates, typically a consequence of suboptimal adherence to regimens requiring three times a day administration and/or large numbers of pills, were common. In a study from the Johns Hopkins HIV clinic in Baltimore, only 37% of their patients starting their first protease inhibitor (PI) based regimen between 1996 and 1998 had HIV viral load levels below the limit of detection (500 copies/mL).2 An analysis of drug resistance from this early era of pote
