Impact of cyp51A mutations on the pharmacokinetic and pharmacodynamic properties of voriconazole in a murine model of disseminated aspergillosis

Abstract

The in vivo efficacy of voriconazole against 4 clinical Aspergillus fumigatus isolates with MICs ranging from 0.125 to 2 mg/liter (CLSI document M38A) was assessed in a nonneutropenic murine model of disseminated aspergillosis. The study involved TR/L98H, M220I, and G54W mutants and a wild-type control isolate. Oral voriconazole therapy was started 24 h after intravenous infection of mice and was given once daily for 14 consecutive days, with doses ranging from 10 to 80 mg/kg of body weight, using survival as the endpoint. Survival for all isolates was dependent on the voriconazole dose level (R(2) value of 0.5 to 0.6), but a better relationship existed for the area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC/MIC ratio) or the AUC for the free, unbound fraction of the drug divided by the MIC (fAUC/MIC ratio) (R(2) value of 0.95 to 0.98). The 24-h fAUC/MIC ratio showed a clear relationship to effect, with an exposure index for amount of free drug required for 50% of maximum effectiveness (fEI(50)) of 11.17 at day 7. Maximum effect was reached at values of around 80 to 100, comparable to that observed for posaconazole and A. fumigatus. Mice infected with an isolate having a MIC of 2 mg/liter required an exposure that was inversely correlated with the increase in MIC compared to that of the wild-type control, but due to nonlinear pharmacokinetics, this required only doubling of the voriconazole dose. The efficacy of voriconazole for isolates with high MICs for other triazoles but voriconazole MICs within the wild-type population range was comparable to that for the wild-type control. Finally, we used a grapefruit juice-free murine model of aspergillosis and concluded that this model is appropriate to study pharmacokinetic/pharmacodynamic relationships of voriconazole.

FIG. 1.

Efficacy of voriconazole monotherapy at 10, 40 (all isolates), and 80 (TR/L98H isolate) mg/kg, depicted by strain. Placebo groups received saline. For all groups, n = 11.

FIG. 2.

Plasma voriconazole concentrations after administration of oral doses of 10, 40, and 80 mg/kg to immunocompetent infected mice. Each symbol corresponds to the geometric mean standard deviation of plasma levels for three mice.

FIG. 3.

Voriconazole dose-survival relationships for four A. fumigatus isolates. Voriconazole treatment improved the survival of the infected mice in a dose-dependent manner for all four isolates. The curves indicate fits with the Hill equation for each isolate.

FIG. 4.

Survival as a function of voriconazole dose/MIC ratio for mice infected with four A. fumigatus isolates at two different time points. In mice infected with the TR/L98H isolate (MIC of 2 mg/liter), doubling of the dose to 80 mg/kg was required in order to achieve a similar outcome (100%) to that for the groups infected with a wild-type isolate (MIC of 0.25 mg/liter). The curve is the model fit with the Hill equation for pooled data.

FIG. 5.

Statistical timed analysis of survival as a function of voriconazole AUC/MIC ratio for four A. fumigatus isolates. Increased voriconazole exposure was required to obtain maximum efficacy in mice infected by isolates with attenuated susceptibility. The curve is the model fit with the Hill equation for pooled data.

FIG. 6.

Survival as a function of fAUC/MIC ratio for four A. fumigatus isolates. Based on the voriconazole exposure data after oral administration of 10, 40, and 80 mg/kg, an fAUC/MIC ratio of 80 to 100 might protect against azole-resistant A. fumigatus species with MICs reaching 2 mg/liter. The curve is the model fit with the Hill equation for pooled data.

FIG. 7.

Channels 1 and 2 of the G54W and M220I α-demethylase mutants are accessible for voriconazole (B and C), whereas they are closed through a position change of Y107 by the L98H mutation (A). The two ligand access channels are indicated in green. The heme cofactor is indicated in black.