Influence of a Combined Pharmacogenetic Score on Through Plasma Voriconazole Concentrations in Haematological Patients

Voriconazole (VRC), the gold-standard treatment of invasive aspergillosis is characterized by variables and nonlinear pharmacokinetics, causing many under- or over-dosing. A link exist between trough plasma concentrations (Cmin) of VRC and effectiveness but also its toxicity. Thus the longitudinal therapeutic drug monitoring of VRC is now recommended with a therapeutic range between 1 and 5 mg/L. The pharmacokinetic variability of VRC is in part explained by its metabolism, mainly dependent on cytochrome P 450 (CYP), particularly CYP2C19, 3A4, 3A5; all these CYP exhibiting genetic polymorphisms. The authors, recently shown, and for the first time , in a retrospective study conducted in 29 patients allogeneic hematopoietic stem cell that initial VRC Cmin adjusted the dose was not only influenced by the route of administration but also by a pharmacogenetics score whose determination is to assign each genotype CYP2C19 and CYP3A a score expressed in a arbitrary units.

The combined pharmacogenetic score was strongly correlated with the original Cmin (r= -0.748; p = 0.002) and was the only independent predictor of initial Cmin (after adjusting the dose and the route of administration). In addition, none of the patients having a genetic score <2 (ie metabolizing capacity of reduced VRC) did not show an initial Cmin below 1 mg/L, while the initial Cmin was below this threshold efficiency in 47% of patients with a genetic score >2. The aim of this new study is to confirm the impact of the pharmacogenetic score on the initial VRC Cmin over a larger prospective cohort of 60 adult patients with onco-hematological diseases.