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Background:  CPCRA 064 is a randomized, prospective, clinical endpoint trial (n = 274) for patients with multi-drug resistant virus. Reported previously, the study was closed to enrollment early (June 2002) due to safety concerns in the structured treatment interruption arm. Follow-up of all patients continues. We report changes in resistance patterns during the structured treatment interruption for 137 patients.

Methods:  Patients were randomized to a 4-month structured treatment interruption. Resistance assays include phenotype (PART) and genotype (GART) at screening, month 2 (GART only), month 4, and structured treatment interruption discontinuation. Patients are grouped by actual structured treatment interruption duration:  group A (at least 4 months, n = 97), group B (>2 but <4 months, mean = 2.9, n = 29), and group C (<2 months, mean = 1.4, n = 11). We report the number of mutations, number of sensitive drugs by GART (GSS) and PART (PSS), and changes in CD4⁺ count and HIV RNA.

Results:  For each group, the mean number of mutations decreased during the structured treatment interruption in each class. For groups A, B, and C, the GSS increased at DC by 8.1, 6.1, and 3.1, respectively. For group C, who reinitiated therapy prior to month 2, the mean number of mutations at month 4 was greater than at screening. Also, the GSS at discontinuation is smaller and the percentage decline in CD4⁺ count and increase in HIV RNA at month 1 is greater for group C.