An important
element in antimicrobial stewardship programmes is early switch from intravenous (i.v.) to oral antimicrobial treatment, especially for highly bioavailable drugs. The
antifungal agent voriconazole is available both in i.v. and oral formulations and bioavailability is estimated to be >90% in healthy volunteers, making this drug a suitable candidate for such a transition. Recently, two studies have shown that the bioavailability of
voriconazole is substantially lower in patients. However, for both studies various factors that could influence the
voriconazole serum concentration, such as
inflammation, concomitant intake of food with oral
voriconazole, and gastrointestinal complications, were not included in the evaluation. Therefore, in this study a retrospective chart review was performed in adult patients treated with both oral and i.v.
voriconazole at the same dose and within a limited (≤5 days) time interval in order to evaluate the effect of switching the route of administration on
voriconazole serum concentrations. A total of 13 patients were included. The mean
voriconazole trough concentration was 2.28 mg/L [95% confidence interval (CI) 1.29-3.26 mg/L] for i.v.
voriconazole administration and 2.04 mg/L (95% CI 0.78-3.30 mg/L) for
oral administration. No significant difference was found in the mean oral and i.v. trough concentrations of
voriconazole (P = 0.390). The mean bioavailability was 83.0% (95% CI 59.0-107.0%). These findings suggest that factors other than bioavailability may cause the observed difference in
voriconazole trough concentrations between oral and i.v. administration in the earlier studies and stress the need for an antimicrobial stewardship team to guide
voriconazole dosing.