GW433908/ritonavir once daily in antiretroviral therapy-naive HIV-infected patients: absence of protease resistance at 48 weeks

To investigate the emergence of resistance to GW433908 (908), a protease inhibitor (PI) with demonstrated antiviral efficacy, safety and tolerability, when administered once daily (q.d.) with low dose ritonavir (908/r). A 48-week Phase III open-label study (SOLO, APV30002) in which antiretroviral therapy-naive patients (n = 649) were treated with 908/r, (1400 mg/200 mg, q.d.) or nelfinavir [1250 mg, twice daily (b.i.d.)] with two nucleoside reverse transcriptase inhibitors (NRTI), abacavir (300 mg, b.i.d.) and lamivudine (150 mg, b.i.d.). Viral genotype and phenotype were analysed at baseline and on treatment up to 48 weeks and beyond. Emergence of genotypic resistance was significantly different between the 908/r q.d. and the nelfinavir b.i.d, treatment arms for both PIs (0 versus 50%; P < 0.001) and the NRTI (13% versus 69%; P < 0.001) received. In the nelfinavir arm the key protease mutations D30N and/or L90M were frequently observed. The absence of protease resistance mutations and reduced incidence of NRTI resistance mutations in the 908/r q.d. arm was confirmed by phenotyping, which showed a lack of PI cross-resistance. The absence of resistance to 908 or cross-resistance to other PIs, and reduced NRTI resistance, following a 908/r q.d. regimen supports the use of this boosted PI early in therapy.