Comparison of genotypic and phenotypic resistance patterns of human immunodeficiency virus type 1 isolates from patients treated with stavudine and didanosine or zidovudine and lamivudine

Sequencing of reverse-transcriptase genes and recombinant virus assays were performed on paired isolates from antiretroviral drug-naive patients rando mized to stavudine and didanosine (group 1; n = 21) or zidovudine and lamiv udine (group 2; n = 21) at baseline and after greater than or equal to 12 m onths of follow-up. The T215Y mutation emerged in 13 (61.9%) and 2 (9.5%) i solates in groups 1 and 2, respectively (P < .0001). Furthermore, in group 1, mutations associated with multi-dideoxynucleoside resistance were select ed in 3 isolates. In group 2, all isolates carried the M184V mutation. The median fold changes in susceptibilities to zidovudine, stavudine, and lamiv udine were 16.4 and 1, 2.2 and 0.6, and 4.5 and >38 in groups 1 and 2, resp ectively (P < .0001, all comparisons). These results suggest that the combi nation of stavudine and didanosine is associated more frequently with the e mergence of zidovudine resistance and a decrease in susceptibility to stavu dine than the combination of zidovudine and lamivudine.