Given the limited treatment options for patients with high-level resistance, antiretroviral (ARV) regimens based on concomitant use of 2 ritonavir (RTV)-boosted protease inhibitors (PIs) were considered a therapeutic option. Boehringer Ingelheim (BI) study 1182.51 examined the pharmacokinetic profile, safety, and efficacy of RTV-boosted tipranavir (TPV/r), alone and in combination with comparator PIs (CPIs) in 315 triple-class-experienced, HIV-infected patients. Two weeks after single PI therapy, the addition of TPV/r reduced plasma trough levels 52%, 80%, and 56% for lopinavir (LPV), saquinavir (SQV), and amprenavir (APV) recipients, respectively. After 2 weeks, a TPV/r-only regimen reduced HIV viral load (VL) by a median of 1.06 log(10) copies/mL. VL reductions at 2 weeks between single-boosted CPIs were difficult to compare, because the numbers of patients maintaining their previous failing PI after randomization were different. At week 4, patients initiating treatment with TPV-containing regimens sustained VL reduction (median decrease of 1.27 log(10) copies/mL). Patients adding TPV to regimens at week 2 achieved median reductions from a baseline of 1.19 log(10), 0.96 log(10), and 1.12 log(10) copies/mL at week 4 in dual-boosted LPV, SQV, and APV groups, respectively. At 24 weeks, VL reductions (median: -0.24 to -0.47 log(10) copies/mL) were comparable between treatment groups. The efficacy of a dual PI regimen depended on the presence of TPV, with additional recycled CPIs having limited activity, even in drug-resistant patient populations with plasma trough concentrations regarded as likely to be adequate in this study. No clear guidelines exist about ARV plasma trough concentrations in treatment-experienced patients, however.

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