Atazanavir: The Advent of a New Generation of More Convenient Protease Inhibitors

[Viral resistance and genetic barrier of atazanavir]

Resistance to protease inhibitors (PI) is generally due to a mutation in the protease gene. Different changes have been described for each PI. The I 50L mutation is characteristic of resistance to atazanavir (ATV). It does not produce cross resistance to other PI; but it does increase susceptibility to all of them (hypersusceptibility). When PI are given concomitantly with low doses of ritonavir, the exposure to higher levels of PI requires that multiple resistance mutations have to be selected in the protease so that there is a significant loss of susceptibility. For the majority of PI/r, including ATV/r, >or=5 mutations in the protease are required to produce a compromise in the virological response. Despite having a moderate genetic barrier when not boosted with ritonavir, the prolonged half life of ATV minimises the risk of resistance in clinical practice.

Plasma levels of atazanavir and the risk of hyperbilirubinemia are predicted by the 3435C-->T polymorphism at the multidrug resistance gene 1

The 3435C-->T polymorphism at the multidrug resistance gene 1 (MDR1) was examined in 74 patients with human immunodeficiency virus who initiated atazanavir therapy. The MDR1 genotype distribution at position 3435 was 28% CC, 45% CT, and 27% TT. Plasma levels of atazanavir were significantly higher in patients with genotype CC than in those with CT or TT, and bilirubin levels correlated with atazanavir concentrations.