Trial participants received either once-daily elvitegravir (150 mg or 85 mg) or twice-daily raltegravir (400 mg). Patients’ background regimens were based on the results of resistance testing and included a fully-active ritonavir-boosted protease inhibitor, and a second agent that was permitted to be a nucleoside or nucleotide reverse transcriptase inhibitor, etravirine, maraviroc or enfuvirtide. Due to known pharmacokinetic interactions, patients randomized to elvitegravir whose background protease inhibitor was either atazanavir or lopinavir received an 85 mg dose of elvitegravir.In January 2011, Gilead announced that it would extend the blinded, randomized period of Study 145 from the originally planned 48 weeks to 96 weeks in order to obtain longer-term safety and efficacy data. Based on the achievement of the non-inferiority endpoint at 48 weeks, patients continued to receive the regimen to which they were originally randomized in a blinded fashion through 96 weeks. Secondary endpoints included additional measures of the efficacy, safety and tolerability of the two treatment regimens. At baseline, the median HIV RNA in the elvitegravir and raltegravir arms, respectively, was 4.35 log 10 copies/mL and 4.42 log 10 copies/mL. Median CD4 cell counts were 227 cells/mm 3 and 215 cells/mm 3 for the elvitegravir and raltegravir arms, respectively. Mean increases in CD4 cell counts at Week 96 were 205 cells/mm 3 for elvitegravir patients and 198 cells/mm 3 for raltegravir patients. Virologic failure rates were similar in both arms: 26 percent for elvitegravir patients and 29 percent for raltegravir patients. Of those patients randomized, 7 percent of patients in each arm developed an integrase resistance mutation. The most common Grade 2-4 adverse events occurring in greater than or equal to 5 percent of patients in either treatment arm were diarrhea, back pain, depression, bronchitis, upper respiratory tract infection, sinusitis, arthralgia and urinary tract infection. The incidence of these adverse events was similar in both treatment arms with the exception of diarrhea, which was more common in the elvitegravir arm (p=0.02).