Lisa K. Naeger

Boceprevir- and telaprevir-based treatments for chronic hepatitis C virus (HCV) infection use specific response-guided therapy (RGT) guidelines. Eligibility for shortened treatment duration is based on achieving undetectable HCV RNA early during treatment. It is unclear whether a detected HCV RNA level that is below the assay lower limit of quantitation (detectable/BLOQ) is comparable to an undetectable HCV RNA level for RGT decision making. We analyzed data from boceprevir and telaprevir clinical trials to obtain a comprehensive understanding of the frequency and clinical relevance of detectable/BLOQ HCV RNA measurements. In Phase 3 trials P05216 (boceprevir), C216 (telaprevir), and 108 (telaprevir), detectable/BLOQ levels were reported for approximately 10%-20% of all on-treatment HCV RNA measurements. In P05216 and C216, subjects with detectable/BLOQ HCV RNA, on average, had a reduced sustained virologic response (SVR) rate compared with subjects with undetectable HCV RNA at the same on-treatment timepoint. At key RGT timepoints (week 8 for boceprevir, week 4 for telaprevir), subjects with detectable/BLOQ HCV RNA had an approximately 20% lower SVR rate compared with subjects with undetectable HCV RNA, and this difference widened for later on-treatment timepoints. A similar trend was observed for Study 108, but the differences in SVR rates were modest, potentially explained by a higher frequency of reported detectable/BLOQ results. Analyses of Phase 2 boceprevir and telaprevir trials indicated subjects with detectable/BLOQ HCV RNA at RGT timepoints benefited from extended treatment duration. Conclusion: During boceprevir- and telaprevir-based treatment, subjects with detectable/BLOQ HCV RNA had a reduced virologic response compared with subjects with undetectable HCV RNA. Eligibility for shortened treatment duration should be based on achieving undetectable HCV RNA (i.e., HCV RNA not detected) at RGT decision timepoints. (Hepatology 2012)

To assess the resistance profile of tipranavir. Resistance analyses were performed on Boëhringer Ingelheim-sponsored studies examining the safety and efficacy of tipranavir in highly treatment-experienced individuals at 24 weeks. Virologic response rates based on the presence of baseline primary protease inhibitor mutations and based on baseline tipranavir susceptibility were evaluated, and the development of protease mutations during treatment with tipranavir was analyzed. Virologic response rates in tipranavir-treated individuals were reduced when isolates with substitutions at amino acid positions I13, V32, M36, I47, Q58, D60 V82 or I84 were present at baseline. In addition, virologic response rates to tipranavir decreased when the number of baseline protease inhibitor (PI) mutations was five or more. Individuals who received tipranavir without concomitant enfurvitide and had five or more baseline PI mutations group began to lose antiviral response between weeks 4 and 8. However, individuals taking enfuvirtide with tipranavir were able to achieve greater than 1.5 log10 reductions in viral load from baseline out to 24 weeks even if they had five or more baseline PI mutations. Virologic response rates to tipranavir decreased when the baseline phenotype for tipranavir had a greater than three-fold shift in the 50% effective concentration (EC50) from reference. The most common protease mutations that developed in tipranavir-treated individuals who experienced virologic failure were L10I/V/S, I13V, L33V/I/F, M36V/I/L V82T, V82L, and I84V. The resistance profile in treatment-naive individuals was not characterized. Baseline genotypic and phenotypic data provide valuable information on the likelihood of a virologic response to tipranavir.

To assess the virologic response rates of atazanavir/ritonavir and lopinavir/ritonavir based on baseline genotype and phenotype. Resistance analyses were performed on a Bristol-Myers Squibb-sponsored study comparing the safety and efficacy of atazanavir/ritonavir to lopinavir/ritonavir in treatment-experienced subjects at 48 weeks. Analyses evaluated virologic response based on the presence of baseline primary protease inhibitor mutations and baseline susceptibility. Less than 30% of atazanavir/ritonavir-treated patients were responders if substitutions at positions M46, G73, I84 or L90 were present in their HIV at baseline. In comparison, lopinavir/ritonavir response rates were less than 30% when protease substitutions at M46, I54, or I84 were present at baseline. The response rates were similar between atazanavir/ritonavir and lopinavir/ritonavir-treated subjects with zero to four baseline protease inhibitor mutations, but response rates were reduced if five or more baseline mutations were present: 0% for atazanavir/ritonavir compared with 28% for lopinavir/ritonavir. Baseline phenotype results showed that response rates were similar between atazanavir/ritonavir and lopinavir/ritonavir if shifts in susceptibility were zero to five, but response rates were lower if shifts were greater than five; 11% for atazanavir/ritonavir compared with 27% for lopinavir/ritonavir. Both type and number of baseline protease inhibitor mutations affected virologic response to atazanavir/ritonavir and lopinavir/ritonavir in treatment-experienced subjects. In addition, baseline phenotypic susceptibility could differentiate virologic response rates to the two drugs. These resistance analyses provide information on the likelihood of a virologic response to antiretroviral drugs based on baseline genotypic and phenotypic data, which is valuable to physicians and patients when choosing antiretroviral regimens.