Simplification to atazanavir/ritonavir monotherapy
POSTSCRIPT NOTE: Please note that subsequent studies have raised serious cautions against the strategy of boosted atazanavir monotherapy and that this is no longer recommended even within a study setting. 
Simon Collins, HIV i-Base
Susan Swindells and colleagues from University of Nebraska presented results from a study that switched 36 patients who had suppressed viral load <50 copies/mL for at least one year on their first PI-based triple therapy (with 2 RTIs), to atazanavir/ritonavir maintenance therapy. 
The primary endpoint of the study was viral suppression <200 copies/mL at 24 weeks after stopping the RTIs.
The median follow-up was 194 days (range 84 to 345). Two patients discontinued the study before switching (one withdrew consent and one had viral rebound >50 copies/mL. Of the 34 remaining patients, three experienced viral rebound at 12, 14 and 24 weeks to 1285, 4730, and 28,397 copies/mL respectively. Two of these patients had no detectable levels of atazanavir at failure, the third resuppressed to <50 copies/mL while on ATZ/r alone. PI resistance was not detected at failure in these three patients. There were no treatment discontinuations for adverse events after simplification.
The observed virologic success 24 weeks after simplification was 91% (lower 90% CI limit = 85%).
Please note that subsequent studies have raised serious cautions against the strategy of boosted atazanavir monotherapy and that this is no longer recommended even within a study setting. 
- Swindells S, Wilkin T, DiRienzo G et al. A prospective, open-label, pilot trial of regimen simplification to atazanavir/ritonavir alone as maintenance antiretroviral therapy after sustained virologic suppression (ACTG 5201). 13th Conference on Retroviruses and Opportunistic Infections, 5- February 2006, Denver. Oral late breaker abstract 108LB.
- Karlstrom et al. Early virologic rebound in a pilot trial of ritonavir-boosted atazanavir as maintenance monotherapy. J Acquir Immune Defic Syndr. 2007 Apr 1;44(4):417-22.
http://www.ncbi.nlm.nih.gov/pubmed/17159658 Full text on Medscape.