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Excerpt
[Little SJ et al. N Engl J Med 2002;347:385]
This is a multicenter study of resistance test results in HIV strains from untreated patients with acute HIV infection or seroconversion within the previous 6 months from May 1995 through June 2000 in 10 cities in the U.S. and Canada. Results were analyzed separately for 264 patients studied from 1995–98 and 113 patients studied from 1999–2000. Phenotypic resistance was examined in all patients, and genotypic resistance was studied in most. High-level phenotypic resistance was defined as a 50% inhibitory concentration (IC50) value exceeding 10-fold higher for the test strain compared to a drug-sensitive reference strain. Results showed that high-level resistance increased from 3.4% in the early period of study to 12.4% in the 1999–2000 period (p = 0.002). The frequency of resistance mutation by genotypic resistance testing increased from 8% in the early period to 22.7% in the more recent period. Data for the outcome of treatment was available in 74% of the 377 participants. This showed that the median time to viral suppression was 56 days in patients with a susceptible virus compared to 88 days for those with a IC50 > 10. Those with a susceptible virus also had a longer period preceding relapse following viral suppression. The results of the resistance assays are summarized in Table 5.
