hiv treatment guidelines from the us department of health and human services ( dhhs ) have endorsed regimen simplification or switching in treatmentexperienced patients with suppressed viraemia . one simplification strategy is the discontinuation of lowdose ritonavir once viral suppression has been achieved , which has been shown in some studies to improve tolerability and reduce toxicities [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ] . depending on the other regimen components , ritonavir discontinuation may also eliminate concern about cytochrome p4503a ( cyp3a)mediated drug interactions with other drugs [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ] . while atazanavir is a generally welltolerated protease inhibitor ( pi ) whose plasma concentration and genetic barrier to resistance are improved by coadministration with ritonavir , the combination is also associated with an increased risk of indirect hyperbilirubinaemia [ 11 , 12 , 13 ] , which , when accompanied by scleral icterus , can prompt treatment discontinuation . this study , assure ( a 
 simplification study of unboosted reyataz with epzicom ) , investigated the efficacy and safety of discontinuing ritonavir in virologically suppressed participants receiving a regimen of tenofovir / emtricitabine  +  atazanavir / ritonavir ( tdf / ftc  +  atv / r ) , one of the recommended firstline regimens in the dhhs guidelines . as tdf / ftc is not recommended for use with unboosted atv because of a drug  drug interaction that results in decreased concentrations of atv , participants in this trial who were randomized to discontinue ritonavir simultaneously switched to a nucleoside reverse transcriptase inhibitor ( nrti ) backbone of abacavir / lamivudine ( abc/3tc ) . this paper presents the 48week results of this study , including virological efficacy , immunological response , safety , tolerability , and hiv1 genotypic and phenotypic resistance patterns in participants who experienced confirmed virological failure . changes from baseline in fasting lipids and in biomarkers associated with cardiovascular , bone and renal health were also evaluated . the prospective , randomized , multicentre , openlabel , phase iv assure study ( epz113734 ; nct01102972 ) enrolled hiv1infected , antiretroviral ( art)experienced adults ( 18 years of age ) who were receiving a oncedaily regimen of tdf / ftc ( 300 mg/200  mg )  +  atv / r ( 300  mg/100  mg ) for at least 6 months prior to the first day of screening . eligible participants were virologically suppressed ( defined as hiv1 rna    75 hiv1 rna copies / ml ) at two consecutive timepoints ( including the screening visit and one additional visit at least 28 days prior to screening ) . tdf / ftc  +  atv / r could be a participant 's initial regimen or first or second switch regimen ( defined as any change in art components ) as long as there was no documented history of virological failure . all previous art regimens consisted of two nrtis ( either tdf / ftc or zidovudine / lamivudine ) plus either a food and drug administration ( fda)licensed nonnucleoside reverse transcriptase inhibitor ( nnrti ) or a ritonavirboosted pi , although alternative prior regimens were allowed on a casebycase basis . participants were excluded if they were human leucocyte antigen ( hla)b*5701positive , or had prior abacavir exposure , active centers for disease control and prevention ( cdc ) clinical category c disease , ongoing clinically relevant hepatitis and/or chronic hepatitis b virus ( hbv ) infection [ hbv surface antigen positive ( hbsag+ ) ] or a creatinine clearanc  <  50  ml / min via the cockroft  gault method . while a baseline genotype was not required , participants were deemed ineligible if they had known hiv genotyping results that indicated the presence of any nrti or pi mutation associated with resistance to any study drug . women of childbearing potential were eligible if they had negative pregnancy tests at screening and baseline and agreed to use protocolprescribed contraception methods throughout the study . additional information on inclusion / exclusion criteria , including a link to the study protocol , is available in a previous publication . all participants provided written informed consent to participate in the study , and the protocol was approved by the institutional review board for each study site . after stratification by prior art experience ( tdf / ftc  +  atv / r as initial regimen or as first / second switch regimen ) , eligible participants were randomized 2:1 to simplify their regimen to oncedaily abc/3tc 600  mg/300  mg ( viiv healthcare , research triangle park , nc ) plus 400  mg atv once daily ( two 200 mg tablets ; bristolmyers squibb , princeton , nj ) or to remain on oncedaily tdf / ftc ( gilead sciences , foster city , ca ) plus one 300  mg atv tablet boosted with a 100  mg ritonavir tablet ( abbvie , chicago , il ) . randomization and study drug provisioning were performed by glaxosmithkline 's randomization and medication ordering system . participants were evaluated at screening , baseline , and weeks 2 , 4 , 12 , 24 , 36 and 48 ; visits included routine chemistry , haematology , hiv1 rna and immunology assessments . the concentrations of specific biomarkers [ bone alkaline phosphatase ( bap ) , parathyroid hormone ( pth ) , cterminal telopeptide ( ctelopeptide ) , osteocalcin , urine 2 microglobulin ( 2m):creatinine ratio , highsensitivity creactive protein ( hscrp ) , interleukin6 and ddimer ] were evaluated at baseline , week 24 and week 48 ( as were vitamin d levels ) . hiv1 rna concentrations were measured using the realtime hiv1 assay ( abbott molecular , inc . , des plaines , il ) . adverse events and laboratory toxicities were graded using the 2004 division of aids toxicity grading scale . glomerular filtration rates ( gfrs ) were estimated using the modification of diet in renal disease ( mdrd ) formula . smoking status and presence of diabetes were assessed at baseline , week 24 and week 48 for framingham risk score calculation ; treatmentemergent changes in fasting total , highdensity lipoprotein ( hdl ) and lowdensity lipoprotein ( ldl ) cholesterol and triglycerides were assessed using the division of aids lipid toxicity grading system . viral genotypes and phenotypes were determined by monogram biosciences ( south san francisco , ca ) ; mutations were defined according to international aids society  usa guidelines . all other laboratory tests were performed centrally by quest diagnostics ( van nuys , ca ) . the intenttotreat ( itt ) population consisted of all enrolled participants randomized in the study . the primary population for efficacy analyses included all participants in the itt population who received at least one dose of study drug [ ittexposed ( itte ) ] . the virological failure population included all participants who met the protocoldefined criteria for confirmed virological failure , defined as plasma hiv1 rna    400 copies / ml on two consecutive occasions . the observed data set contained all data collected while participants were in the study ; no missing values were imputed . the primary efficacy endpoint was the proportion of participants with hiv1 rna  <  50 copies / ml at week 24 by the time to loss of virological response ( tlovr ) algorithm . the proportion of participants with hiv1 rna  <  50 copies / ml at week 48 was a secondary endpoint . other secondary endpoints included the proportion of participants with hiv1 rna  <  400 copies / ml , the change from baseline in cd4 cell count , time to virological failure , detection of genotypic and phenotypic resistance at the time of virological failure , change from baseline in fasting lipid profiles ( total , ldl and hdl cholesterol and triglycerides ) , grade 24 aes and all saes . there were two exploratory endpoints : ( 1 ) change from baseline in neurocognition scores , to be reported in a separate paper ; and ( 2 ) change from baseline in eight cardiovascular / inflammation , bone and renal biomarkers , included in this publication . per protocol , virological response rates at week 48 were compared using a cochran   mantelhaenszel test stratified by initial art regimen ( tdf / ftc  +  atv / r as initial regimen or as first / second switch regimen ) . continuous variables were assessed using the wilcoxon ranksum test , and binary responses were compared using fisher 's exact test . biomarker data were logtransformed prior to analysis , and the change from baseline was assessed using geometric mean ratios with 95% confidence intervals . the statistical analyses were performed using sas version 9.1 ( sas institute inc . , cary , nc ) . after stratification by prior art experience ( tdf / ftc  +  atv / r as initial regimen or as first / second switch regimen ) , eligible participants were randomized 2:1 to simplify their regimen to oncedaily abc/3tc 600  mg/300  mg ( viiv healthcare , research triangle park , nc ) plus 400  mg atv once daily ( two 200 mg tablets ; bristolmyers squibb , princeton , nj ) or to remain on oncedaily tdf / ftc ( gilead sciences , foster city , ca ) plus one 300  mg atv tablet boosted with a 100  mg ritonavir tablet ( abbvie , chicago , il ) . randomization and study drug provisioning were performed by glaxosmithkline 's randomization and medication ordering system . participants were evaluated at screening , baseline , and weeks 2 , 4 , 12 , 24 , 36 and 48 ; visits included routine chemistry , haematology , hiv1 rna and immunology assessments . the concentrations of specific biomarkers [ bone alkaline phosphatase ( bap ) , parathyroid hormone ( pth ) , cterminal telopeptide ( ctelopeptide ) , osteocalcin , urine 2 microglobulin ( 2m):creatinine ratio , highsensitivity creactive protein ( hscrp ) , interleukin6 and ddimer ] were evaluated at baseline , week 24 and week 48 ( as were vitamin d levels ) . hiv1 rna concentrations were measured using the realtime hiv1 assay ( abbott molecular , inc . , des plaines , il ) . adverse events and laboratory toxicities were graded using the 2004 division of aids toxicity grading scale . glomerular filtration rates ( gfrs ) were estimated using the modification of diet in renal disease ( mdrd ) formula . smoking status and presence of diabetes were assessed at baseline , week 24 and week 48 for framingham risk score calculation ; treatmentemergent changes in fasting total , highdensity lipoprotein ( hdl ) and lowdensity lipoprotein ( ldl ) cholesterol and triglycerides were assessed using the division of aids lipid toxicity grading system . viral genotypes and phenotypes were determined by monogram biosciences ( south san francisco , ca ) ; mutations were defined according to international aids society  usa guidelines . all other laboratory tests were performed centrally by quest diagnostics ( van nuys , ca ) . the intenttotreat ( itt ) population consisted of all enrolled participants randomized in the study . the primary population for efficacy analyses included all participants in the itt population who received at least one dose of study drug [ ittexposed ( itte ) ] . the virological failure population included all participants who met the protocoldefined criteria for confirmed virological failure , defined as plasma hiv1 rna    400 copies / ml on two consecutive occasions . the observed data set contained all data collected while participants were in the study ; no missing values were imputed . the primary efficacy endpoint was the proportion of participants with hiv1 rna  <  50 copies / ml at week 24 by the time to loss of virological response ( tlovr ) algorithm . the proportion of participants with hiv1 rna  <  50 copies / ml at week 48 was a secondary endpoint . other secondary endpoints included the proportion of participants with hiv1 rna  <  400 copies / ml , the change from baseline in cd4 cell count , time to virological failure , detection of genotypic and phenotypic resistance at the time of virological failure , change from baseline in fasting lipid profiles ( total , ldl and hdl cholesterol and triglycerides ) , grade 24 aes and all saes . there were two exploratory endpoints : ( 1 ) change from baseline in neurocognition scores , to be reported in a separate paper ; and ( 2 ) change from baseline in eight cardiovascular / inflammation , bone and renal biomarkers , included in this publication . per protocol , virological response rates at week 48 were compared using a cochran   mantelhaenszel test stratified by initial art regimen ( tdf / ftc  +  atv / r as initial regimen or as first / second switch regimen ) . continuous variables were assessed using the wilcoxon ranksum test , and binary responses were compared using fisher 's exact test . biomarker data were logtransformed prior to analysis , and the change from baseline was assessed using geometric mean ratios with 95% confidence intervals . the statistical analyses were performed using sas version 9.1 ( sas institute inc . , cary , nc ) . this study enrolled 297 participants from 43 clinical sites in the usa and puerto rico . one participant randomized to tdf / ftc  +  atv / r was withdrawn because of a protocol violation prior to receiving any study medication , so the itte population included 199 participants simplifying to abc/3tc  +  atv and 97 continuing on tdf / ftc  +  atv / r . participants were recruited between april 2010 and december 2011 , and the last 48week analysis visit occurred in december 2012 . most participants ( 79% ) were male ( table  1 ) , 34% were of africanamerican / african heritage , and 26% selfidentified as hispanic / latino . median time on art prior to enrolment was 978 days for the abc/3tc  +  atv group and 1106 days for the tdf / ftc  +  atv / r group . baseline participant demographics and characteristics abc/3tc , abacavir / lamivudine ; art , antiretroviral therapy ; atv , atazanavir ; atv / r , atazanavir / ritonavir ; cdc , centers for disease control and prevention ; tdf / ftc , tenofovir / emtricitabine . eightyfive per cent ( 253 ) of participants in the itte population completed 48 weeks on study ( fig .  1 ) . the most common reasons for study withdrawal were lost to followup ( 5% ; 15 participants ) , consent withdrawn ( 4% ; 12 participants ) , and aes ( 3% ; 10 participants ) . all adverse events leading to study discontinuation were grade 1 or 2 , with the exception of a grade 3 lipase increase in one participant continuing on tenofovir / emtricitabine  +  atazanavir / ritonavir ( tdf / ftc  +  atv / r ) . abc/3tc , abacavir / lamivudine ; atv , atazanavir ; atv / r , atazanavir / ritonavir ; tdf / ftc , tenofovir / emtricitabine . as previously reported , 86.9% ( 173 of 199 ) of participants in the abc/3tc  +  atv treatment group successfully maintained hiv1 rna  <  50 copies / ml by the tlovr analysis at week 24 compared with 86.6% ( 84 of 97 ) in the tdf / ftc  +  atv / r group . the adjusted treatment difference was 0.33% , and the twosided 95% confidence interval ( ci ) ( 7.97 to 8.64% ) stratified by prior art regimen excluded the predefined noninferiority margin of 12% , demonstrating the noninferiority of the abc/3tc  +  atv simplification regimen to the tdf / ftc  +  atv / r continuation regimen . at week 48 , the efficacy results were also similar between treatment groups ( p  =  0.564 ) , with 76% ( 152 of 199 ) of participants taking abc/3tc  +  atv and 79% ( 77 of 97 ) taking tdf / ftc  +  atv / r having hiv1 rna  <  50 copies / ml by tlovr analysis . in the observed analysis , there was no significant difference ( p  =  0.134 ) in hiv1 rna  <  50 copies / ml at week 48 between treatment groups , with response rates of 91% ( 154 of 169 ) in the abc/3tc  +  atvtreated group versus 96% ( 79 of 82 ) in the tdf / ftc  +  atv / rtreated group . there was no significant difference between treatment groups by tlovr analysis in the hiv1 rna  <  50 copies / ml response rate when adjusted by gender ( p  =  0.672 ) , race ( p  =  0.645 ) or age ( p  =  0.652 ) . at week 48 , median cd4 cell counts were 603 and 590 cells/l for abc/3tc  +  atv and tdf / ftc  +  atv / r , respectively . however , the median increase in cd4 cell count from baseline to week 48 was significantly larger ( p  =  0.026 ) in the abc/3tc  +  atv group ( + 90 cells/l ) compared with the tdf / ftc  +  atv / r group ( + 47 cells/l ) . confirmed virological failure occurred in four of 199 ( 2% ) participants switched to abc/3tc  +  atv and one of 97 ( 1% ) participants continuing on tdf / ftc  +  atv / r . at virological failure , hiv1 from three participants ( two receiving abc/3tc  +  atv ; one receiving tdf / ftc  +  atv / r ) was fully susceptible to all drugs , with no reverse transcriptase ( rt ) mutations and a few minor pi mutations ( including l10i , g16g / e , d60e , i62v , v77i and i93l ) detected , and confirmed virological failure was associated with site reports of noncompliance and/or therapy interruption . one abc/3tc  +  atvreceiving participant experienced initial rebound at day 14 , concomitant with sitereported treatment compliance issues . no prior hiv1 genotypes or comprehensive treatment records were available , but the participant reported receiving nevirapine plus tdf / ftc for > 8 years before tdf / ftc  +  atv / r . numerous hiv1 rt mutations ( m41l , l74v , k103n , m184v , l210w and t215y ) were detected , including thymidine analogue mutations ( tams ) , despite no prior reported zidovudine or stavudinecontaining treatment . multiple pi mutations ( l10f , k20i , m46i , i54v , i62v , l63p , a71 t , g73 t , i84v and l90 m ) were detected . the participant 's hiv1 had reduced phenotypic susceptibility to multiple drugs , including abc , 3tc and atv . several years of prior treatment with tdf / ftc and efavirenz before switching to a tdf / ftc  +  atv / r regimen were reported . the m41l and t215y tams and the m184v mutation were detected at failure , despite no prior reported zidovudine or stavudine treatment , as were numerous pi mutations ( l10i , k20r , l24i , m36i , k43 t , m46l , i62v , v82a and l89 m ) ; the virus from this participant remained susceptible to both abc and tdf but had reduced susceptibility to atv and 3tc / ftc . rates of aes of moderate or greater severity ( grade 24 ) were similar between the two groups ( 45% for both groups ; table  2 ) . there were few grade 24 treatmentrelated aes in either group ( 9% for abc/3tc  +  atv and 6% for tdf / ftc  +  atv / r ) . five participants experienced grade 24 cardiac disorders during the course of the study ; none were considered to be drug related . in the tdf / ftc  +  atv / r group , one participant had grade 2 palpitations . in the abc/3tc  +  atv group , two participants were diagnosed with grade 2 cardiomyopathy ; the third had a prior history of congestive heart failure and developed grade 2 coronary artery disease , and the fourth participant , a former smoker with diabetes , hyperlipidaemia , and a family history of cardiovascular disease , had a grade 4 acute inferior myocardial infarction . adverse events and laboratory abnormalities listing includes all events occurring in more than one participant . abc/3tc , abacavir / lamivudine ; ae , adverse event ; atv , atazanavir ; atv / r , atazanavir / ritonavir ; ldl , lowdensity lipoprotein ; tdf / ftc , tenofovir / emtricitabine . adverse events leading to study withdrawal affected 4% of participants receiving abc/3tc  +  atv and 2% of participants continuing on tdf / ftc  +  atv / r ; of these , only nausea , vomiting and rash were reported in more than one participant . suspected abc hypersensitivity was reported for one participant during the course of the study ; the participant was not withdrawn but restarted his original tdf / ftc  +  atv / r regimen with resolution of signs and symptoms . the rate of treatmentemergent or worsening grade 24 ( p  =  0.0026 ) and grade 34 ( p  =  0.0014 ) laboratory abnormalities was significantly higher in the tdf / ftc  +  atv / r group compared with the abc/3tc  +  atv group . other treatmentemergent grade 34 laboratory abnormalities were infrequent and similar between groups ( table  2 ) . the fasting lipid levels for participants with paired baseline and week 48 results ( fig . 2 ) were similar between treatment groups and varied little between baseline and week 48 , except for a small but statistically significant increase in median hdl cholesterol levels ( 3.0  mg / dl ; p  =  0.013 ) for the abc/3tc  +  atv group . median fasting lipid parameters with guideline cutoffs from the national cholesterol education program ( ncep )   for participants with paired baseline and week 48 values . a significant increase ( p  <  0.0001 ) in median highdensity lipoprotein ( hdl ) cholesterol levels for the change from baseline ( cfb ) to week 48 was seen for the abacavir / lamivudine  +  atazanavir ( abc/3tc  +  atv ) group with no significant increase in the tenofovir / emtricitabine  +  atazanavir / ritonavir ( tdf / ftc  +  atv / r ) treatment group ( p  =  0.8994 ) ; a significant difference ( p  =  0.013 ) between treatment groups was also observed . abc/3tc , abacavir / lamivudine ; atv , atazanavir ; atv / r , atazanavir / ritonavir ; ldl , lowdensity lipoprotein ; tdf / ftc , tenofovir / emtricitabine . at baseline , the median estimated glomerular filtration rate by the mdrd equation was 93  ml / min/1.73  m for both treatment groups . at week 48 , there was a small median increase of 0.8  ml / min/1.73  m for the abc/3tc  +  atv group and a small median decrease of 1.3  ml / min/1.73  m in the tdf / ftc  +  atv / r group , but this effect was not statistically significant . the median 10year risk of coronary heart disease as measured by the framingham equation at baseline and week 48 was 2.0% and 2.0% , respectively , for the abc/3tc  +  atv group and 1.5% and 2.0% for the tdf / ftc  +  atv / r group , respectively . between baseline and week 48 , there was a significant ( p  <  0.001 ) decrease resulting in improvement for the measured bone biomarkers bap , pth , ctelopeptide and osteocalcin in the abc/3tc  +  atv group ( fig . 3a  d ) ; these biomarkers remained relatively unchanged in the tdf / ftc  +  atv / r group over the same time period . comparing the two treatment groups , the decrease from baseline to week 48 in all four of these bone biomarkers was significantly larger ( p  <  0.001 ) for the abc/3tc  +  atv group than for the tdf / ftc  +  atv / r group . serum calcium levels remained similar within and between groups , with baseline mean values of 9.33 and 9.35  mg / dl for the abc/3tc  +  atv and tdf / ftc  +  atv / r groups , respectively , and mean changes of 0.05 and 0.02  mg / dl , respectively , at week 48 . vitamin d ( 25 oh ) geometric mean values were in the low but normal range at baseline ( 28.3  ng / ml in the abc/3tc  +  atv group and 26.4  ng / ml in the tdf / ftc  +  atv / r group ) . at week 48 , these values were 24.6  ng / ml in the abc/3tc  +  atv group and 29.3  ng / ml in the tdf / ftc  +  atv / r group , representing a decline from baseline for the abc/3tc  +  atv group ( p  <  0.001 ) and an increase for the tdf / ftc  +  atv / r group ( p  =  0.005 ) . biomarkers . geometric means and 95% confidence intervals for the bone biomarkers ( a ) bone alkaline phosphatase , ( b ) parathyroid hormone , ( c ) cterminal telopeptide and ( d ) osteocalcin ; ( e ) the renal biomarker urine 2 microglobulin : creatinine ratio ; and the inflammatory biomarkers ( f ) highsensitivity creactive protein ( hscrp ) , ( g ) interleukin6 and ( h ) ddimer in participants from both treatment groups with data at baseline and week 48 . intraarm pvalues were calculated using a paired ttest on the ratio of the geometric mean concentration at baseline and the geometric mean concentration at week 48 . interarm pvalues were calculated using a twosample ttest on the ratio of the geometric mean change from baseline to week 48 in the abacavir / lamivudine  +  atazanavir ( abc/3tc  +  atv ) versus tenofovir / emtricitabine  +  atazanavir / ritonavir ( tdf / ftc  +  atv / r ) groups . abc/3tc , abacavir / lamivudine ; atv , atazanavir ; atv / r , atazanavir / ritonavir ; tdf / ftc , tenofovir / emtricitabine . the renal biomarker 2m : creatinine ratio declined by 56% in the abc/3tc  +  atv group ( p  <  0.001 ) but increased by 14% in the tdf / ftc  +  atv / r group ( fig . 3e ) ; the change from baseline to week 48 was significantly different ( p  < conversely , there were no significant changes from baseline to week 48 in any of the biomarkers associated with cardiovascular disease , inflammation or thrombogenesis that were evaluated ( hscrp , interleukin6 and ddimer ) either within or between treatment groups ( fig . this study enrolled 297 participants from 43 clinical sites in the usa and puerto rico . one participant randomized to tdf / ftc  +  atv / r was withdrawn because of a protocol violation prior to receiving any study medication , so the itte population included 199 participants simplifying to abc/3tc  +  atv and 97 continuing on tdf / ftc  +  atv / r . participants were recruited between april 2010 and december 2011 , and the last 48week analysis visit occurred in december 2012 . most participants ( 79% ) were male ( table  1 ) , 34% were of africanamerican / african heritage , and 26% selfidentified as hispanic / latino . median time on art prior to enrolment was 978 days for the abc/3tc  +  atv group and 1106 days for the tdf / ftc  +  atv / r group . baseline participant demographics and characteristics abc/3tc , abacavir / lamivudine ; art , antiretroviral therapy ; atv , atazanavir ; atv / r , atazanavir / ritonavir ; cdc , centers for disease control and prevention ; tdf / ftc , tenofovir / emtricitabine . eightyfive per cent ( 253 ) of participants in the itte population completed 48 weeks on study ( fig .  1 ) . the most common reasons for study withdrawal were lost to followup ( 5% ; 15 participants ) , consent withdrawn ( 4% ; 12 participants ) , and aes ( 3% ; 10 participants ) . all adverse events leading to study discontinuation were grade 1 or 2 , with the exception of a grade 3 lipase increase in one participant continuing on tenofovir / emtricitabine  +  atazanavir / ritonavir ( tdf / ftc  +  atv / r ) . abc/3tc , abacavir / lamivudine ; atv , atazanavir ; atv / r , atazanavir / ritonavir ; tdf / ftc , tenofovir / emtricitabine . as previously reported , 86.9% ( 173 of 199 ) of participants in the abc/3tc  +  atv treatment group successfully maintained hiv1 rna  <  50 copies / ml by the tlovr analysis at week 24 compared with 86.6% ( 84 of 97 ) in the tdf / ftc  +  atv / r group . the adjusted treatment difference was 0.33% , and the twosided 95% confidence interval ( ci ) ( 7.97 to 8.64% ) stratified by prior art regimen excluded the predefined noninferiority margin of 12% , demonstrating the noninferiority of the abc/3tc  +  atv simplification regimen to the tdf / ftc  +  atv / r continuation regimen . at week 48 , the efficacy results were also similar between treatment groups ( p  =  0.564 ) , with 76% ( 152 of 199 ) of participants taking abc/3tc  +  atv and 79% ( 77 of 97 ) taking tdf / ftc  +  atv / r having hiv1 rna  <  50 copies / ml by tlovr analysis . in the observed analysis , there was no significant difference ( p  =  0.134 ) in hiv1 rna  <  50 copies / ml at week 48 between treatment groups , with response rates of 91% ( 154 of 169 ) in the abc/3tc  +  atvtreated group versus 96% ( 79 of 82 ) in the tdf / ftc  +  atv / rtreated group . there was no significant difference between treatment groups by tlovr analysis in the hiv1 rna  <  50 copies / ml response rate when adjusted by gender ( p  =  0.672 ) , race ( p  =  0.645 ) or age ( p  =  0.652 ) . at week 48 , median cd4 cell counts were 603 and 590 cells/l for abc/3tc  +  atv and tdf / ftc  +  atv / r , respectively . however , the median increase in cd4 cell count from baseline to week 48 was significantly larger ( p  =  0.026 ) in the abc/3tc  +  atv group ( + 90 cells/l ) compared with the tdf / ftc  +  atv / r group ( + 47 cells/l ) . confirmed virological failure occurred in four of 199 ( 2% ) participants switched to abc/3tc  +  atv and one of 97 ( 1% ) participants continuing on tdf / ftc  +  atv / r . at virological failure , hiv1 from three participants ( two receiving abc/3tc  +  atv ; one receiving tdf / ftc  +  atv / r ) was fully susceptible to all drugs , with no reverse transcriptase ( rt ) mutations and a few minor pi mutations ( including l10i , g16g / e , d60e , i62v , v77i and i93l ) detected , and confirmed virological failure was associated with site reports of noncompliance and/or therapy interruption . one abc/3tc  +  atvreceiving participant experienced initial rebound at day 14 , concomitant with sitereported treatment compliance issues . no prior hiv1 genotypes or comprehensive treatment records were available , but the participant reported receiving nevirapine plus tdf / ftc for > 8 years before tdf / ftc  +  atv / r . numerous hiv1 rt mutations ( m41l , l74v , k103n , m184v , l210w and t215y ) were detected , including thymidine analogue mutations ( tams ) , despite no prior reported zidovudine or stavudinecontaining treatment . multiple pi mutations ( l10f , k20i , m46i , i54v , i62v , l63p , a71 t , g73 t , i84v and l90 m ) were detected . the participant 's hiv1 had reduced phenotypic susceptibility to multiple drugs , including abc , 3tc and atv . several years of prior treatment with tdf / ftc and efavirenz before switching to a tdf / ftc  +  atv / r regimen were reported . the m41l and t215y tams and the m184v mutation were detected at failure , despite no prior reported zidovudine or stavudine treatment , as were numerous pi mutations ( l10i , k20r , l24i , m36i , k43 t , m46l , i62v , v82a and l89 m ) ; the virus from this participant remained susceptible to both abc and tdf but had reduced susceptibility to atv and 3tc / ftc . rates of aes of moderate or greater severity ( grade 24 ) were similar between the two groups ( 45% for both groups ; table  2 ) . there were few grade 24 treatmentrelated aes in either group ( 9% for abc/3tc  +  atv and 6% for tdf / ftc  +  atv / r ) . five participants experienced grade 24 cardiac disorders during the course of the study ; none were considered to be drug related . in the tdf / ftc  +  atv / r group , one participant had grade 2 palpitations . in the abc/3tc  +  atv group , two participants were diagnosed with grade 2 cardiomyopathy ; the third had a prior history of congestive heart failure and developed grade 2 coronary artery disease , and the fourth participant , a former smoker with diabetes , hyperlipidaemia , and a family history of cardiovascular disease , had a grade 4 acute inferior myocardial infarction . adverse events and laboratory abnormalities listing includes all events occurring in more than one participant . abc/3tc , abacavir / lamivudine ; ae , adverse event ; atv , atazanavir ; atv / r , atazanavir / ritonavir ; ldl , lowdensity lipoprotein ; tdf / ftc , tenofovir / emtricitabine . adverse events leading to study withdrawal affected 4% of participants receiving abc/3tc  +  atv and 2% of participants continuing on tdf / ftc  +  atv / r ; of these , only nausea , vomiting and rash were reported in more than one participant . suspected abc hypersensitivity was reported for one participant during the course of the study ; the participant was not withdrawn but restarted his original tdf / ftc  +  atv / r regimen with resolution of signs and symptoms . the rate of treatmentemergent or worsening grade 24 ( p  =  0.0026 ) and grade 34 ( p =  0.0014 ) laboratory abnormalities was significantly higher in the tdf / ftc  +  atv / r group compared with the abc/3tc  +  atv group . other treatmentemergent grade 34 laboratory abnormalities were infrequent and similar between groups ( table  2 ) . the fasting lipid levels for participants with paired baseline and week 48 results ( fig . 2 ) were similar between treatment groups and varied little between baseline and week 48 , except for a small but statistically significant increase in median hdl cholesterol levels ( 3.0  mg / dl ; p  =  0.013 ) for the abc/3tc  +  atv group . median fasting lipid parameters with guideline cutoffs from the national cholesterol education program ( ncep )   for participants with paired baseline and week 48 values . a significant increase ( p  <  0.0001 ) in median highdensity lipoprotein ( hdl ) cholesterol levels for the change from baseline ( cfb ) to week 48 was seen for the abacavir / lamivudine  +  atazanavir ( abc/3tc  +  atv ) group with no significant increase in the tenofovir / emtricitabine  +  atazanavir / ritonavir ( tdf / ftc  +  atv / r ) treatment group ( p  =  0.8994 ) ; a significant difference ( p  =  0.013 ) between treatment groups was also observed . abc/3tc , abacavir / lamivudine ; atv , atazanavir ; atv / r , atazanavir / ritonavir ; ldl , lowdensity lipoprotein ; tdf / ftc , tenofovir / emtricitabine . at baseline , the median estimated glomerular filtration rate by the mdrd equation was 93  ml / min/1.73  m for both treatment groups . at week 48 , there was a small median increase of 0.8  ml / min/1.73  m for the abc/3tc  +  atv group and a small median decrease of 1.3  ml / min/1.73  m in the tdf / ftc  +  atv / r group , but this effect was not statistically significant . the median 10year risk of coronary heart disease as measured by the framingham equation at baseline and week 48 was 2.0% and 2.0% , respectively , for the abc/3tc  +  atv group and 1.5% and 2.0% for the tdf / ftc  +  atv / r group , respectively . between baseline and week 48 , there was a significant ( p  <  0.001 ) decrease resulting in improvement for the measured bone biomarkers bap , pth , ctelopeptide and osteocalcin in the abc/3tc  +  atv group ( fig . 3a  d ) ; these biomarkers remained relatively unchanged in the tdf / ftc  +  atv / r group over the same time period . comparing the two treatment groups , the decrease from baseline to week 48 in all four of these bone biomarkers was significantly larger ( p  <  0.001 ) for the abc/3tc  +  atv group than for the tdf / ftc  +  atv / r group . serum calcium levels remained similar within and between groups , with baseline mean values of 9.33 and 9.35  mg / dl for the abc/3tc  +  atv and tdf / ftc  +  atv / r groups , respectively , and mean changes of 0.05 and 0.02  mg / dl , respectively , at week 48 . vitamin d ( 25 oh ) geometric mean values were in the low but normal range at baseline ( 28.3  ng / ml in the abc/3tc  +  atv group and 26.4  ng / ml in the tdf / ftc  +  atv / r group ) . at week 48 , these values were 24.6  ng / ml in the abc/3tc  +  atv group and 29.3  ng / ml in the tdf / ftc  +  atv / r group , representing a decline from baseline for the abc/3tc  +  atv group ( p  <  0.001 ) and an increase for the tdf / ftc  +  atv / r group ( p  =  0.005 ) . biomarkers . geometric means and 95% confidence intervals for the bone biomarkers ( a ) bone alkaline phosphatase , ( b ) parathyroid hormone , ( c ) cterminal telopeptide and ( d ) osteocalcin ; ( e ) the renal biomarker urine 2 microglobulin : creatinine ratio ; and the inflammatory biomarkers ( f ) highsensitivity creactive protein ( hscrp ) , ( g ) interleukin6 and ( h ) ddimer in participants from both treatment groups with data at baseline and week 48 . intraarm pvalues were calculated using a paired ttest on the ratio of the geometric mean concentration at baseline and the geometric mean concentration at week 48 . interarm pvalues were calculated using a twosample ttest on the ratio of the geometric mean change from baseline to week 48 in the abacavir / lamivudine  +  atazanavir ( abc/3tc  +  atv ) versus tenofovir / emtricitabine  +  atazanavir / ritonavir ( tdf / ftc  +  atv / r ) groups . abc/3tc , abacavir / lamivudine ; atv , atazanavir ; atv / r , atazanavir / ritonavir ; tdf / ftc , tenofovir / emtricitabine . the renal biomarker 2m : creatinine ratio declined by 56% in the abc/3tc  +  atv group ( p  <  0.001 ) but increased by 14% in the tdf / ftc  +  atv / r group ( fig . 3e ) ; the change from baseline to week 48 was significantly different ( p  < conversely , there were no significant changes from baseline to week 48 in any of the biomarkers associated with cardiovascular disease , inflammation or thrombogenesis that were evaluated ( hscrp , interleukin6 and ddimer ) either within or between treatment groups ( fig . in this randomized , multicentre assure study , the proportion of participants maintaining suppression of hiv1 rna  <  50 copies / ml by tlovr at week 48 was similar between participants switching to abc/3tc  +  atv ( 76% ) and those maintaining on tdf / ftc  +  atv / r ( 79% ) . the efficacy and tolerability of abc/3tc  +  atv demonstrated in this study complement those observed in the aries trial , where artnave patients initiated treatment with abc/3  tc  +  atv / r , and after 36 weeks the virologically suppressed population was randomized to continue on the same regimen or switch to a regimen of abc/3tc  +  atv . viral suppression was maintained 48 weeks postrandomization in 86% of patients in the abc/3tc  +  atvtreated group and in 81% of those taking abc/3tc +  atv / r , accompanied by lower rates of treatmentrelated grade 2    4 aes and a decrease in hyperbilirubinaemia from 14% to 4% for the abc/3tc  +  atvtreated group . in assure , switching to abc/3tc  +  atv was also accompanied by fewer treatmentemergent or worsening aes , driven largely by a lower rate of moderate to severe hyperbilirubinaemia and by a modest but significant increase in median cd4 cell count . similarly , in the induma study , previously antiretroviralnave patients received two nrtis plus atv / r for 26 to 30 weeks , and virologically suppressed patients were randomized to unboosted atv or maintained atv / r . after 48 weeks there was no significant difference in virological suppression between the groups ( 78% for atv and 75% for atv / r ) , while hyperbilirubinaemia decreased by 50% ( from 32 to 16% ) in the unboosted atv group . in the assure study , significant improvements in the bone turnover markers pth , bap , ctelopeptide and osteocalcin were observed following the switch to abc/3tc  +  atv , with little change over time in the tdf / ftc  +  atv / r group . initiation of art is often associated with decreases in bone mineral density that slow or stabilize over 24 to 48 weeks of therapy ; these losses tend to be larger with tdfcontaining regimens compared with nontdfcontaining regimens [ 20 , 21 , 22 , 23 ] . bone biomarkers have been studied in treatmentnave patients initiating therapy [ 24 , 25 , 26 , 27 ] , but few randomized trials have included treatmentexperienced adults [ 28 , 29 , 30 ] ; results from these treatmentexperienced studies were generally consistent with our findings that bone biomarkers were more favourable in patients taking abc/3tc compared with tdf / ftc and probably reflect clinically relevant differences between these regimens in bone turnover . the improvement in bone markers observed after switching from tdf in our study was not explained by changes in levels of calcium or vitamin d. vitamin d levels at baseline and at week 48 remained within the lower end of the normal range for both treatment groups , and a small decline was noted for these levels in the abc/3tc  +  atv treatment group . switching to abc/3tc  +  atv also resulted in improvement in the 2m : creatinine ratio , a validated marker of combined glomerular and tubular health . while the association between tdf and renal impairment is well studied ( for example [ 31 , 32 , 33 , 34 ] , ) , only one randomized trial , assert , which compared abc/3tc with tdf / ftc both in combination with efavirenz in treatmentnave patients , has included the 2m : creatinine ratio . after 48 weeks on therapy , the 2m : creatinine ratio increased by 24% in the tdf / ftc group and decreased by 47% in the abc/3tc group ( p  <  0.0001 ) , a result consistent with the results observed in assure ( albeit in treatmentnave patients ) . in this study , switching to abc/3tc  +  atv was not associated with significant changes in the markers of inflammation and coagulation , interleukin6 , hscrp and ddimer . several studies found no increase in markers of cardiovascular disease with initiation of abc compared with other nrtis [ 28 , 29 , 34 , 35 , 36 , 37 , 38 , 39 ] , while study a5202 reported a significant increase from baseline in hscrp after 96 weeks in treatmentnave patients randomized to abc/3tc , with no significant change in patients randomized to tdf / ftc , although interleukin6 levels decreased significantly in both the abc/3tc and tdf / ftctreated groups . four other studies have examined cardiovascular markers in treatmentexperienced patients : steal , swap , bicombo , and swift . as in our study , none of these trials reported a difference between abc/3tc and tdf / ftc in hscrp , interleukin6 or ddimer over 48 weeks of postrandomization treatment . wildtype virus at virological failure was detected in three of five participants with confirmed viraemia  > two additional participants , both receiving abc/3tc  +  atv , experienced virological failure , one shortly after therapy switch ( day 14 ) and one at week 36 . multiple viral resistance mutations , including tams , were detected in virus from both participants , and the k103n nnrti mutation was detected in one participant . as tams are not selected by treatment with either tdf / ftc or abc/3tc , these results are suggestive of these participants having previously experienced treatment failure on either zidovudine or stavudinecontaining regimens , although no prior exposure was reported for either participant . there are several limitations of this trial that should be considered when interpreting results from this study . this simplification treatment strategy is restricted to certain nrti backbones such as abc/3tc that can be used in combination with unboosted atv . the study enrolled virologically suppressed , therapyexperienced patients and was designed to exclude those patients with prior virological failure that could have resulted in selection for drug resistanceassociated viral mutations affecting resistance to the investigational products . plasma concentrations of atv in the absence of ritonavir boosting are lower , and therefore this regimen may be more susceptible to patient adherence issues , especially if archived resistanceassociated mutations are present . while the markers of bone density examined are considered accepted markers of bone turnover , this study did not directly measure bone density . over 48 weeks , discontinuation of ritonavir after switching from a regimen of tdf / ftc  +  atv / r to abc/3tc  +  atv maintained viral suppression in study participants and led to improvements in cd4 cell count , the bone biomarkers pth , bap , ctelopeptide and osteocalcin , and the renal 2m : creatinine ratio . the abc/3tc  +  atv treatment group also had significantly fewer laboratory abnormalities than the tdf / ftc  +  atv / r treatment group without increasing other fasting lipid levels or cardiovascular biomarkers of inflammation and thrombogenesis . substantial contributions to study conception and design were made by daw , dam , hhz , llr and mss . substantial contributions to the analysis and interpretation of the data were made by hhz , daw , llr , dam and mss . substantial contributions to acquisition of patient clinical study data were made by daw , lb , cbs , he , ed and wgw . all authors ( daw , dam , hhz , llr , mss , lb , cbs , he , ed and wgw ) had full access to the data and vouch for the accuracy and completeness of the data and analyses . the manuscript was written and approved by all of the authors , each of whom contributed to the drafts and revisions .
objectives 
 hiv treatment guidelines endorse switching or simplification of antiretroviral therapy in therapyexperienced patients with suppressed viraemia ; ritonavir discontinuation may also enhance tolerability and reduce longterm adverse events ( aes ) . 
 this openlabel , multicentre , noninferiority study enrolled hiv1infected , treatmentexperienced adults with confirmed hiv1 rna    75 hiv1 rna copies / ml currently receiving tenofovir / emtricitabine  +  atazanavir / ritonavir ( tdf / ftc  +  atv / r ) for   6 months with no reported history of virological failure.methodsparticipants were randomized 1:2 to continue current treatment or switch to abacavir / lamivudine + atazanavir ( abc/3tc  +  atv ) . 
 endpoints included the proportion of participants with hiv1 rna  <  50 copies / ml by time to loss of virological response ( tlovr ) , aes , fasting lipids , and inflammatory , coagulation , bone and renal biomarkers.resultsafter 48 weeks , 76% ( 152 of 199 ) of abc/3tc  +  atvtreated and 79% ( 77 of 97 ) of tdf / ftc  +  atv / rtreated participants had hiv1 rna  <  50 copies / ml ( tlovr ; p  =  0.564 ) . 
 other efficacy analyses yielded similar results . 
 rates of new grade 24 aes were 45% in both groups , but an excess of hyperbilirubinaemia made the rate of treatmentemergent grade 34 laboratory abnormalities higher with tdf / ftc  +  atv / r ( 36% ) compared with abc/3tc  +  atv ( 19% ) . 
 most fasting lipid levels remained stable over time ; highdensity lipoprotein ( hdl ) cholesterol increased modestly in abc/3tc  +  atvtreated participants . 
 bone and renal biomarkers improved significantly between baseline and week 48 in participants taking abc/3tc  +  atv and were stable in participants taking tdf / ftc  +  atv / r . 
 no significant changes occurred in any inflammatory or coagulation biomarker within or between treatment groups.conclusionsthe abc/3tc  +  atv treatmentswitch group had similar viral suppression rates up to 48 weeks to the tdf / ftc  +  atv / r comparator group , with lower rates of moderate to highgrade hyperbilirubinaemia and improvements in bone and renal biomarkers .