Lower dose of Norvir is more effective

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This is guaranteed to mess with some people's minds.

Once-Daily Fosamprenavir With 100 vs 200 mg of Ritonavir8th International Congress on Drug Therapy in HIV InfectionNovember 12-16, 2006Glasgow, ScotlandMark Mascolini (via NATAP)Once-daily fosamprenavir with a 100-mg ritonavir boost improved virologic responses after 24 weeks compared with the standard 200-mg boost [1]. But Duke University's Hicks and coworkers from other US sites warned these preliminary results must be weighed cautiously because people randomized to 200 mg of ritonavir started treatment with more advanced HIV infection.The ongoing trial involves 115 antiretroviral-naive people who began 1400 mg of fosamprenavir with either 100 or 200 mg of ritonavir plus once-daily fixed-dose 3TC/abacavir. While 53% in both groups were African American, 81% were men. Median age stood at about 40 years when the trial began. The 57 people who got a 200-mg ritonavir boost had more advanced disease than those who started with a 100-mg boost (Table).Pretreatment HIV disease status in a trial of once-daily fosamprenavirSix people quit the 200-mg ritonavir arm before week 24, 1 because of virologic failure, 3 because of side effects, 6 who stopped coming back for visits, and 1 who broke trial rules. Five people dropped out of the 100-mg arm, none because of virologic failure, 1 because of side effects, 3 who stopped coming back for visits, and 1 for breaking study rules.After 24 weeks an intent-to-treat (missing-data-equal-failure) analysis determined that 90% in the 100-mg ritonavir group and 75% in the 200-mg group had a viral load under 400 copies/mL, virtually a significant difference (P = 0.051). Respective percentages for a 400-copy on-treatment analysis were 98% and 86%, a significant difference (P = 0.027). Twenty-four week results significantly favored the 100-mg group in analyses of 50-copy response rates (86% versus 67% intent to treat, P = 0.009; 96% versus 76% on treatment, P = 0.004). Average CD4 gains were equivalent in the two study arms, rising from 242 to 368 with a 100-mg boost and from 211 to 353 with the 200-mg boost.Besides the convenience of swallowing 100 versus 200 mg of ritonavir, the lower dose may also be assumed to ease side-effect and lipid rates. But that did not happen through 24 weeks of follow-up. Whereas 21 people (36%) had a grade 2 to 4 side effect in the 100-mg group, 23 (40%) did in the 200-mg arm. Diarrhea may have been slightly more common with 200 mg of ritonavir (10 versus 6 people, 18% versus 10%). But abdominal pain bothered 3 people taking the 100-mg dose (5%) and none taking 200 mg. Pretreatment and 24-week cholesterol and triglyceride readings did not differ much between the two study groups. Hicks and colleagues noted that an earlier comparison of 100 versus 200 mg of ritonavir to boost fosamprenavir found 38% lower amprenavir trough concentrations with the smaller boost. But in that study trough levels with 100 mg of ritonavir stayed above the average amprenavir 50% inhibitory concentration for fosamprenavir-susceptible virus.Reference1. Hicks C, DeJesus E, Sloan L, et al. Efficacy and safety of once-daily boosted fosamprenavir/ritonavir with abacavir/lamivudine (3TC) fixed dose combination in antiretroviral naive HIV-1 infected patients: 24-week results from COL100758. 8th International Congress on Drug Therapy in HIV Infection, November 12-16, 2006, Glasgow. Abstract 2.5.