To determine the effect of omeprazole on peak serum concentrations (C(max)) of itraconazole oral solution (IOS), we carried out a randomized, open-label, prospective, crossover study. Fifteen healthy, non-pregnant adults received a single dose of IOS 400 mg on two occasions, at least 7 days apart, with omeprazole 40 mg nightly for 7 days before either IOS dose 1 or 2. C(max), time to C(max) (T(max)) and AUC(0-8) were determined for itraconazole and its active metabolite, hydroxyitraconazole, for each dose and compared. Omeprazole did not significantly affect the C(max), T(max) or AUC(0-8) of itraconazole or hydroxyitraconazole when administered as IOS.