Atazanavir–bilirubin interaction: a pharmacokinetic–pharmacodynamic model

Abstract

Purpose: The aim of this work was to analyze the atazanavir–bilirubin relationship, using a new mathematical approach to pharmacokinetic–pharmacodynamic models, for competitive drug interactions based on Michaelis–Menten equations.

Patients and methods: Because atazanavir induces an increase of plasma bilirubin levels, in a concentration-dependent manner, we developed a mathematical model, based on increments of atazanavir and bilirubin concentrations at steady state, in HIV infected (HIV⁺) patients, and plotted the corresponding nomogram for detecting suboptimal atazanavir exposure.

Results: By applying the obtained model, the results indicate that an absolute value or an increment of bilirubin at steady state below 3.8 µmol/L, are predictive of suboptimal atazanavir exposure and therapeutic failure.

Conclusion: We have successfully implemented a new mathematical approach to pharmacokinetic–pharmacodynamic model for atazanavir–bilirubin interaction. As a result, we found that bilirubin plasma levels constitute a good marker of exposure to atazanavir and of viral suppression.