Variability of voriconazole plasma levels measured by new high-performance liquid chromatography and bioassay methods

Abstract

Voriconazole (VRC) is a broad-spectrum antifungal triazole with nonlinear pharmacokinetics. The utility of measurement of voriconazole blood levels for optimizing therapy is a matter of debate. Available high-performance liquid chromatography (HPLC) and bioassay methods are technically complex, time-consuming, or have a narrow analytical range. Objectives of the present study were to develop new, simple analytical methods and to assess variability of voriconazole blood levels in patients with invasive mycoses. Acetonitrile precipitation, reverse-phase separation, and UV detection were used for HPLC. A voriconazole-hypersusceptible Candida albicans mutant lacking multidrug efflux transporters (cdr1Delta/cdr1Delta, cdr2Delta/cdr2Delta, flu1Delta/flu1Delta, and mdr1Delta/mdr1Delta) and calcineurin subunit A (cnaDelta/cnaDelta) was used for bioassay. Mean intra-/interrun accuracies over the VRC concentration range from 0.25 to 16 mg/liter were 93.7% +/- 5.0%/96.5% +/- 2.4% (HPLC) and 94.9% +/- 6.1%/94.7% +/- 3.3% (bioassay). Mean intra-/interrun coefficients of variation were 5.2% +/- 1.5%/5.4% +/- 0.9% and 6.5% +/- 2.5%/4.0% +/- 1.6% for HPLC and bioassay, respectively. The coefficient of concordance between HPLC and bioassay was 0.96. Sequential measurements in 10 patients with invasive mycoses showed important inter- and intraindividual variations of estimated voriconazole area under the concentration-time curve (AUC): median, 43.9 mg x h/liter (range, 12.9 to 71.1) on the first and 27.4 mg x h/liter (range, 2.9 to 93.1) on the last day of therapy. During therapy, AUC decreased in five patients, increased in three, and remained unchanged in two. A toxic encephalopathy probably related to the increase of the VRC AUC (from 71.1 to 93.1 mg x h/liter) was observed. The VRC AUC decreased (from 12.9 to 2.9 mg x h/liter) in a patient with persistent signs of invasive aspergillosis. These preliminary observations suggest that voriconazole over- or underexposure resulting from variability of blood levels might have clinical implications. Simple HPLC and bioassay methods offer new tools for monitoring voriconazole therapy.

FIG. 1.

Scatter plot of plasma VRC levels measured by HPLC and bioassay using the C. albicans mutant (cdr1Δ/cdr1Δ, cdr2Δ/cdr2Δ, flu1Δ/flu1Δ, mdr1Δ/mdr1Δ, and cnaΔ/cnaΔ). The line of congruence does not deviate from 1. The coefficient of concordance is 0.96.

FIG. 2.

(A) Courses of estimated VRC AUC in 10 patients. (B to D) Individual VRC concentration-time curves. (B) Patient with proven pulmonary aspergillosis, toxic encephalopathy, and mild cholestasis. Increasing VRC blood levels were observed (ΔAUC + 30.9%) despite an unchanged VRC dose (200 mg orally twice daily; a switch from i.v. to oral treatment had occurred). During the entire study period, the patient received esomeprazole. This serious neurological adverse event was probably related to VRC overdosing and completely resolved after stop of VRC therapy. Rechallenge with lower VRC doses (150 mg orally twice daily) was well tolerated. (C) Patient with persistent signs of probable pulmonary aspergillosis. Decreasing VRC exposure was documented (ΔAUC − 77.5%) despite an unchanged VRC dose (200 mg orally twice daily) and absence of comedication interacting with VRC metabolism. The infection responded after increase of the VRC dose to 300 mg orally twice daily. (D) Patient with probable pulmonary aspergillosis and an uneventful clinical course. VRC concentrations were stable (ΔAUC − 9.9%). The VRC dose was 300 mg twice daily, the route was i.v. on days 2 and 7, and there was no comedication interacting with VRC metabolism.