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Background:
Study M98-863 is a randomized, double-blind Phase III study of 653 ARV-naïve
subjects treated with either Kaletra or nelfinavir (NFV), in combination with
d4T/3TC. In an on treatment analysis at Week 48, 93% of subjects in the Kaletra
group vs. 82% in the NFV group had HIV RNA < 400 copies/ml (p< 0.001). 58
Kaletra treated and 102 NFV treated subjects had HIV RNA >400 copies/mL at
Week 24, 32, 40 or 48.
Methods:
Resistance testing results were available for 37/58 Kaletra and 76/102
NFV-treated subjects. Resistance to Kaletra was defined as the appearance of any
primary or active site mutation in protease, and was confirmed by phenotypic
analysis. Resistance to NFV was defined as the appearance of the D30N and/or
L90M mutations. 3TC resistance was defined as the presence of the M184V or I
mutation in RT,
Results:
No evidence (0/37) of genotypic resistance to Kaletra was observed in any of
these isolates from Kaletra-treated subjects through Week 48. In contrast, 25/76
(33%) of isolates from NFV-treated subjects displayed evidence of genotypic
resistance to NFV (p<0.001 for the comparison
between treatment arms). Subsequent to genotypic analysis, 26
Kaletra-treated subjects and 53 NFV-treated subjects had an HIV RNA
determination. 22/26 (86%) Kaletra-treated subjects experienced resuppression
(or initial suppression) to <400 copies/mL compared to only 17/53 (32%)
NFV-treated subjects (p<0.001). 3TC
resistance was noted in 15/37(41%) of Kaletra-treated subjects and 62/76 (82%)
NFV-treated subjects (p<0.001).
Conclusions: There were no significant differences in the duration or level of detectable viremia, or in adherence (as measured by pill counts), between treatment arms in the subjects with available genotype. These results suggest that the genetic barrier to resistance to Kaletra in treatment-naïve subjects is higher than the barrier to NFV resistance. Data through Week 60 will be presented.
