INTRODUCTION: The phase III TITAN trial evaluated the use of darunavir with low-dose ritonavir (DRV/r) 600/100 mg twice daily (bid) compared with lopinavir with low-dose ritonavir (LPV/r) in treatment-experienced, lopinavir-naive patients. This study estimates the cost effectiveness of DRV/r from a US societal perspective when compared with LPV/r in treatment-experienced patients with a profile similar to those TITAN patients who had one or more International AIDS Society - USA (IAS-USA) primary protease inhibitor (PI) resistance-associated mutations (RAMs) at baseline. This population had less advanced HIV disease and a broader range of previous PI exposure/failure (0 - ≥ 2 PIs) at enrollment than those in the darunavir phase IIb POWER trials.
METHODS: An existing Markov model containing six health states defined by CD4 cell count range (>500, 351-500, 201-350, 101-200, 51-100 and 0-50 cells/mm³) and an absorbing state of death was adapted. Baseline demographics, CD4 cell count distribution and antiretroviral drug usage, virological response (at week 24), and immunological response estimates and matching transition probabilities were based on data collected directly from the one or more IAS-USA PI mutation subpopulation during the first 48 weeks of the TITAN trial, as well as from published literature. Patients were assumed to switch to a regimen containing tipranavir plus an optimized background regimen after treatment failure. For each CD4 cell count range or health state, the utility values, HIV and non-HIV-related mortality rates, and non-antiretroviral-related cost of HIV care estimates were derived from published literature. Unit costs were derived from official local sources. A lifetime horizon was taken in the base-case analysis.
RESULTS: The base-case analysis predicted discounted quality-adjusted survival gains of 0.493 quality-adjusted life-years (QALYs) for DRV/r compared with LPV/r, resulting in an incremental cost-effectiveness ratio (ICER) of US$23,057 per QALY gained over a lifetime horizon. Probabilistic sensitivity analysis indicated a 0.754 probability of an ICER below the threshold of US$50,000 per QALY gained. DRV/r remained cost effective over all parameter ranges tested in extensive one-way sensitivity analyses and variability analyses, which examined the impact of input parameter uncertainty and changes in model assumptions and treatment patterns, respectively. Shortening the model time horizon had the largest impact on the ICER, reducing it most notably to US$4919 with a 10-year time horizon.
CONCLUSION: From a US societal perspective and based on an analysis of the patients with primary IAS-USA PI RAMs enrolled in the darunavir phase III TITAN trial, a highly active antiretroviral therapy (HAART) regimen containing DRV/r 600/100 mg bid is estimated to be a cost-effective therapy when compared with a HAART regimen containing LPV/r, for the management of treatment-experienced, PI-resistant, HIV-infected adults with a broad range of previous PI use/failure.
