Darunavir: a review of its use in the management of HIV infection in adults.

UNLABELLED

Darunavir is an oral nonpeptidic HIV-1 protease inhibitor (PI) that is used, together with a low boosting dose of ritonavir, as part of an antiretroviral therapy (ART) regimen in treatment-experienced and -naive patients with HIV-1 infection. Compared with early-generation PIs, boosted darunavir has a high genetic barrier to resistance and is active against multidrug-resistant HIV isolates. In clinical trials in treatment-experienced patients with HIV-1 infection receiving an optimized background regimen (OBR), twice-daily boosted darunavir was more effective than investigator-selected ritonavir-boosted control PIs (CPIs) or ritonavir-boosted lopinavir. In clinical trials in treatment-naive patients with HIV-1 infection receiving a fixed background regimen, once-daily boosted darunavir was noninferior to boosted lopinavir at 48 weeks and more effective than boosted lopinavir at 96weeks. Boosted darunavir was generally well tolerated in patients with HIV-1 infection in clinical trials. It was associated with a lower incidence of diarrhoea than CPIs or lopinavir in treatment-experienced or -naive patients, and fewer lipid abnormalities than lopinavir in treatment-naive patients. Thus, for the management of treatment-experienced or -naive patients with HIV-1 infection, a ritonavir-boosted darunavir-based ART regimen is a valuable treatment option. PHARMACOLOGICAL PROPERTIES: Darunavir is an oral nonpeptidic HIV-1 PI that selectively inhibits the cleavage of HIV gag and gag-pol polyproteins, thereby preventing viral maturation. Darunavir is highly potent against laboratory strains and clinical isolates of wild-type and multidrug-resistant HIV and has limited cytotoxicity. In an in vitro study in MT-2 cells, the potency of darunavir was greater than that of saquinavir, amprenavir, nelfinavir, indinavir, lopinavir and ritonavir. Darunavir binds with high affinity to HIV-1 protease, including multidrug-resistant proteases, and retains potency against multidrug-resistant HIV-1 strains. Although some potential may exist for cross-resistance with amprenavir, darunavir did not display cross-resistance with other PIs in vitro. In a 24-week analysis of pooled data from the POWER 1 and 2 studies in treatment-experienced patients, 11 protease mutations associated with a reduced response to boosted darunavir were identified (V11I, V32I, L33F, I47V, I50V, I54L/M, G73S, L76V, I84V and L89V). The presence of at least three darunavir resistance-associated mutations (prevalent in approximately 7-9% of treatment-experienced patients) together with a high number of protease resistance-associated mutations were required to confer darunavir resistance. In the 48-week analysis of treatment-experienced patients with virological failure in the the TITAN study, fewer in the boosted darunavir group than in the boosted lopinavir group developed additional mutations or lost susceptibility to PIs compared with baseline. In treatment-naive patients, no primary PI-resistance-associated mutations developed in patients with an available genotype at baseline and endpoint during 96 weeks of treatment with boosted darunavir or boosted lopinavir. Oral darunavir, boosted with low-dose ritonavir, is rapidly absorbed, generally reaching peak plasma concentrations within 2.5-4 hours. The bioavailability of oral darunavir is increased by about 30% when taken with food. Darunavir is primarily metabolized by the hepatic cytochrome P450 (CYP) enzymes, primarily CYP3A. The 'boosting' dose of ritonavir acts an an inhibitor of CYP3A, thereby increasing darunavir bioavailability. Drug interactions can result when darunavir is coadministered with other drugs that are inducers or inhibitors of, or act as substrates for, CYP3A. The mean elimination half-life of boosted darunavir is approximately 15 hours. THERAPEUTIC EFFICACY: In treatment-experienced patients with HIV-1 infection, the therapeutic efficacy of oral twice-daily darunavir 600 mg, boosted with ritonavir 100 mg, versus that of investigator selected boosted CPIs (POWER studies) or versus twice-daily boosted lopinavir (administered as a fixed dose combination of lopinavir/ritonavir 400/100 mg) [TITAN study] has been evaluated in phase IIb and III studies. All patients received concurrent treatment with an OBR. Significantly more patients receiving boosted darunavir achieved a viral load reduction from baseline of >or=1 log(10) copies/mL (primary endpoint) than boosted CPI recipients at all timepoints, up to and including the final efficacy analysis at 144 weeks, in the combined analyses of POWER 1 and 2. The efficacy of boosted darunavir was noninferior to that of boosted lopinavir at 48 weeks, and was significantly better than boosted lopinavir at 48 and 96 weeks in the TITAN study, as determined by significantly more patients in the darunavir group than in the lopinavir group achieving a viral load of <400 copies/mL (primary endpoint). In the ARTEMIS study in treatment-naive patients with HIV-1 infection receiving a fixed background regimen of tenofovir and emtricitabine, once-daily boosted darunavir 800 mg was noninferior to boosted lopinavir 800 mg/day at 48 weeks. At 96 weeks, boosted darunavir was found to be more effective than boosted lopinavir, as determined by significantly more patients in the darunavir group than in the lopinavir group achieving a confirmed plasma viral load of <50 copies/mL (primary endpoint).

TOLERABILITY

Boosted darunavir was generally well tolerated in patients with HIV-1 infection in clinical trials, with most events being mild to moderate in severity. At 48-week analyses, the most common adverse events associated with once- or twice-daily boosted darunavir in treatment-experienced or -naive patients were diarrhoea, nausea, headache, upper respiratory tract infection and nasopharyngitis. The most common boosted darunavir-related grade 2-4 laboratory abnormalities in treatment-experienced patients included increased triglycerides and increased total cholesterol. Overall, boosted darunavir was associated with less diarrhoea than CPIs or boosted lopinavir in treatment-experienced and -naive patients, and a lower incidence of grade 2-4 elevations in triglycerides and total cholesterol than boosted lopinavir in treatment-naive patients. Treatment discontinuation because of adverse events occurred in 3% of boosted darunavir recipients and 7% of boosted lopinavir recipients during 48 weeks of therapy in treatment-naive patients. PHARMACOECONOMIC CONSIDERATIONS: Healthcare costs in the UK and US were estimated to be lower with boosted darunavir than with investigator-selected CPIs in treatment-experienced patients with HIV-1 infection in two 1-year cost analyses conducted from the perspective of a healthcare provider and using predicted costs based on CD4+ cell counts and clinical data from the POWER studies. The higher acquisition cost of boosted darunavir compared with CPIs was more than offset by the better efficacy of darunavir. In modelled cost-effectiveness analyses, boosted darunavir was predicted to be cost effective compared with other boosted CPIs in heavily pretreated adults from a healthcare payer perspective in Europe and from a societal perspective in the US. In a further model of a subgroup of patients with at least one primary International AIDS Society-USA PI mutation, boosted darunavir was predicted to be cost effective compared with boosted lopinavir from a healthcare payer perspective in Europe. The incremental costs per quality-adjusted life-year gained were within commonly accepted thresholds in all cost-effectiveness analyses.