***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
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    Input: CONTEXT Abacavir , a nucleoside analogue , has demonstrated suppression of human immunodeficiency virus ( HIV ) replication alone and in combination therapy . However , the role of abacavir in a triple nucleoside combination regimen has not been evaluated against a st and ard protease inhibitor-containing regimen for initial antiretroviral treatment . OBJECTIVE To evaluate antiretroviral equivalence and safety of an abacavir-lamivudine-zidovudine regimen compared with an indinavir-lamivudine-zidovudine regimen . DESIGN AND SETTING A multicenter , phase 3 , r and omized , double-blind trial with an enrollment period from August 1997 to June 1998 , with follow-up through 48 weeks at 73 clinical research units in the United States , Canada , Australia , and Europe . PATIENTS Five hundred sixty-two antiretroviral-naive , HIV-infected adults with a plasma HIV RNA level of at least 10 000 copies/mL and a CD4 cell count of at least 100 x 10(6)/L. INTERVENTIONS Patients were stratified by baseline HIV RNA level and r and omly assigned to receive a combination tablet containing 150 mg of lamivudine and 300 mg of zidovudine twice daily plus either 300 mg of abacavir twice daily and indinavir placebo or 800 mg of indinavir every 8 hours daily plus abacavir placebo . After 16 weeks , patients with confirmed HIV RNA levels greater than 400 copies/mL were eligible to continue receiving r and omized treatment or receive open-label therapy . MAIN OUTCOME MEASURE Virologic suppression , defined as HIV RNA concentration of 400 copies/mL or less at week 48 . RESULTS The proportion of patients who met the end point of having an HIV RNA level of 400 copies/mL or less at week 48 was equivalent in the abacavir group ( 51 % [ 133/262 ] ) and in the indinavir group ( 51 % [ 136/265 ] ) with a treatment difference of -0.6 % ( 95 % confidence interval [ CI ] , -9 % to 8 % ) . In patients with baseline HIV RNA levels greater than 100 000 copies/mL , the proportion of patients achieving less than 50 copies/mL was greater in the indinavir group than in the abacavir group with 45 % ( 45/100 ) vs 31 % ( 30/96 ) and a treatment diference of -14 % ( 95 % CI , -27 % to 0 % ) . The 2 treatments were comparable with respect to their effects on CD4 cell count . There was no difference between groups in the frequency of treatment-limiting adverse events or laboratory abnormalities . One death in the abacavir group was attributed to hypersensitivity reaction , which occurred following rechallenge with abacavir , approximately 3 weeks after initiating study treatment . CONCLUSIONS In this study of antiretroviral-naive HIV-infected adults , the triple nucleoside regimen of abacavir-lamivudine-zidovudine was equivalent to the regimen of indinavir-lamivudine-zidovudine in achieving a plasma HIV RNA level of less than 400 copies/mL at 48 weeks Patients with sustained virological suppression on protease inhibitor (PI)-based therapy were r and omly assigned to switch the PI to nevirapine ( n = 155 ) , efavirenz ( n = 156 ) , or abacavir ( n = 149 ) and were followed for at least 3 years regardless of the discontinuation of assigned therapy . There was a higher probability of maintaining virological suppression after 3 years of follow-up with nevirapine or efavirenz than with abacavir . In contrast , abacavir showed a lower incidence of adverse effects leading to drug discontinuation BACKGROUND Evidence from r and omized controlled trials supports the use of triple therapy . Research is required on the effectiveness of quadruple therapy in comparison to this and the relative effectiveness of specific highly active antiretroviral therapy ( HAART ) combinations . METHODS Antiretroviral-naive individuals ( n = 53 ) with an HIV-1 viral load > 100 000 copies/mL were r and omized to receive  three-drug HAART with zidovudine/lamivudine ( Combivir ) and efavirenz or quadruple therapy with zidovudine/lamivudine/abacavir ( Trizivir ) and efavirenz ( quad regimen ) . Patients continued on HAART for 48 weeks with regular clinical and immunological assessment . St and ard and ultrasensitive ( < 5 copies/mL ) viral load testing was carried out . RESULTS A DAVG ( difference in averages ) analysis of the fall in viral load and increase in CD4 count showed no significant differences between regimens . Triple therapy result ed in a -4.17 log change ( 95 % CI , -4.48 to -3.85 ) and quadruple therapy in a -4.36 log change ( 95 % CI , -4.68 to -4.03 ) in viral load . For CD4 counts , the triple therapy arm increased by 164 cells/mm(3 ) ( 95 % CI 112 - 217 ) and the quadruple arm by 185 ( 95 % CI , 133 - 237 ) . In an intent-to-treat analysis , 77 % of patients in the triple therapy group reached an undetectable viral load ( < 50 copies/mL ) compared with 84.2 % of the quadruple therapy group . For ultrasensitive viral load testing , 23 % and 18 % of each group , respectively , reached undetectable viral loads . The hazard ratio for attaining a viral load of < 5 copies/mL was 0.59 ( 95 % CI , 0.26 - 1.33 ) for quadruple versus triple therapy . Three individuals in the triple therapy arm and nine in the quadruple therapy arm discontinued treatment . CONCLUSIONS No differences in any analyses were observed between a st and ard of care regimen ( zidovudine/lamivudine and efavirenz ) and the quad regimen ( zidovudine/lamivudine/abacavir and efavirenz ) BACKGROUND The use of fixed-dose combination nucleoside reverse-transcriptase inhibitors ( NRTIs ) with a nonnucleoside reverse-transcriptase inhibitor or a ritonavir-boosted protease inhibitor is recommended as initial therapy in patients with human immunodeficiency virus type 1 ( HIV-1 ) infection , but which NRTI combination has greater efficacy and safety is not known . METHODS In a r and omized , blinded equivalence study involving 1858 eligible patients , we compared four once-daily antiretroviral regimens as initial therapy for HIV-1 infection : abacavir-lamivudine or tenofovir disoproxil fumarate (DF)-emtricitabine plus efavirenz or ritonavir-boosted atazanavir . The primary efficacy end point was the time from r and omization to virologic failure ( defined as a confirmed HIV-1 RNA level > or = 1000 copies per milliliter at or after 16 weeks and before 24 weeks , or > or = 200 copies per milliliter at or after 24 weeks ) . RESULTS A scheduled interim review by an independent data and safety monitoring board showed significant differences in virologic efficacy , according to the NRTI combination , among patients with screening HIV-1 RNA levels of 100,000 copies per milliliter or more . At a median follow-up of 60 weeks , among the 797 patients with screening HIV-1 RNA levels of 100,000 copies per milliliter or more , the time to virologic failure was significantly shorter in the abacavir-lamivudine group than in the tenofovir DF-emtricitabine group ( hazard ratio , 2.33 ; 95 % confidence interval , 1.46 to 3.72 ; P<0.001 ) , with 57 virologic failures ( 14 % ) in the abacavir-lamivudine group versus 26 ( 7 % ) in the tenofovir DF-emtricitabine group . The time to the first adverse event was also shorter in the abacavir-lamivudine group ( P<0.001 ) . There was no significant difference between the study groups in the change from the baseline CD4 cell count at week 48 . CONCLUSIONS In patients with screening HIV-1 RNA levels of 100,000 copies per milliliter or more , the times to virologic failure and the first adverse event were both significantly shorter in patients r and omly assigned to abacavir-lamivudine than in those assigned to tenofovir DF-emtricitabine . ( Clinical Trials.gov number , NCT00118898 . OBJECTIVE To compare the efficacy and safety of fixed-dose abacavir/lamivudine ( ABC/3TC ) and tenofovir/emtricitabine ( TDF/FTC ) with ritonavir-boosted atazanavir ( ATV/r ) in treatment-naïve Japanese patients with HIV-1 infection . METHODS A 96-week multicenter , r and omized , open-label , parallel group pilot study was conducted . The endpoints were times to virologic failure , safety event and regimen modification . RESULTS 109 patients were enrolled and r and omly allocated ( 54 patients received ABC/3TC and 55 patients received TDF/FTC ) . All r and omized subjects were analyzed . The time to virologic failure was not significantly different between the two arms by 96 weeks ( HR , 2.09 ; 95 % CI , 0.72 - 6.13 ; p=0.178 ) . Both regimens showed favorable viral efficacy , as in the intention-to-treat population , 72.2 % ( ABC/3TC ) and 78.2 % ( TDF/FTC ) of the patients had an HIV-1 viral load < 50 copies/mL at 96 weeks . The time to the first grade 3 or 4 adverse event and the time to the first regimen modification were not significantly different between the two arms ( adverse event : HR 0.66 ; 95 % CI , 0.25 - 1.75 , p=0.407 ) ( regimen modification : HR 1.03 ; 95 % CI , 0.33 - 3.19 , p=0.964 ) . Both regimens were also well-tolerated , as only 11.1 % ( ABC/3TC ) and 10.9 % ( TDF/FTC ) of the patients discontinued the allocated regimen by 96 weeks . Clinical ly suspected abacavir-associated hypersensitivity reactions occurred in only one ( 1.9 % ) patient in the ABC/3TC arm . CONCLUSION Although insufficiently powered to show non-inferiority of viral efficacy of ABC/3TC relative to TDF/FTC , this pilot trial suggested that ABC/3TC with ATV/r is a safe and efficacious initial regimen for HLA-B*5701-negative patients , such as the Japanese population Background : Long-term antiretroviral therapy , while dramatically reducing HIV-related morbidity and mortality , is associated with metabolic and morphological changes . Peripheral fat loss , lipoatrophy , appears most associated with prolonged therapy with thymidine nucleoside analogues . Methods : A r and omized , open-label , comparative study of switching from a thymidine nucleoside analogue to either tenofovir disoproxil fumarate ( DF ) or abacavir in 105 individuals on successful antiretroviral therapy with clinical ly evident moderate to severe lipoatrophy . Results : Individuals were r and omized to  tenofovir DF ( 52 ) or abacavir ( 53 ) . The switch was well tolerated and the majority of patients completed 48 weeks of study . One individual in the tenofovir DF group and three in the abacavir group discontinued due to drug-related adverse events . Both groups similarly maintained virological control . Limb fat mass increased similarly in both groups : mean increases by week 48 of 329 and 483 g in tenofovir DF and abacavir groups , respectively [ mean 95 % confidence interval for difference , −154.3 ( range −492.8 to 184.3 ) ] . This change from baseline was statistically significant in both groups ( tenofovir DF , P = 0.01 ; abacavir , P = 0.0001 ) . Mean total cholesterol , low density lipoprotein cholesterol and triglycerides improved modestly with switching to tenofovir DF but were unchanged with abacavir . The changes in these parameters were significantly greater in the tenofovir DF arm relative to abacavir . Conclusions : Switching from a thymidine nucleoside analogue to either tenofovir DF or abacavir leads to significant improvement in limb fat mass over 48 weeks . Tenofovir DF may have modest advantages over abacavir for changes in lipids . Peripher 
    Output:
    
Our cumulative , cross-sectional data suggest a similar virological efficacy of abacavir/lamivudine and tenofovir/emtricitabine regardless of the baseline VL