Resistance-related mutations in the HIV-1 protease gene of patients treated for 1 year with the protease inhibitor ritonavir (ABT-538)

Long-term treatment with ritonavir is associated with the emergence of multiple mutations in the HIV-1 protease gene. The mutations L10I, I54V, L63P, A71V, V82A/F and I84V correspond to known drug-resistance mutations for ritonavir and other protease inhibitors. Phenotypic resistance to ritonavir was detected in a majority of ritonavir-treated patients at 1 year of treatment. In addition, long-term ritonavir treatment selects for cross-resistance to the protease inhibitors indinavir and saquinavir. This argues against sequential therapy with several protease inhibitors. Delayed resistance in one patient was accompanied with a prolonged increase in CD4 cell count and decrease in viral load suggesting a temporary benefit of treatment.