Risk of selecting de novo drug-resistance mutations during structured treatment interruptions in patients with chronic HIV infection.

Background: Structured treatment interruption (STI) may allow viral replication in the presence of decreased plasma drug levels, with risk of selection of resistance mutations.

Methods: For patients recruited for an STI study, genotypic resistance testing was performed at baseline (before receipt of any treatment), immediately before the STI, and 2 weeks after each interuption of therapy.

Results: During 20 (18%) of 112 STI cycles (95% CI, 11%-26%), resistance mutations were selected; 6% of the mutations were de novo (i.