Hydroxy Itraconazole (Itraconazole metabolite Hydroxy Itraconazole; R-63373) is an active metabolite of Itraconazole (ITZ), which is a triazole antifungal agent. IC50 & Target: AntifungalIn Vitro: Hydroxy Itraconazole (Itraconazole metabolite Hydroxy Itraconazole; R-63373) is an active metabolite of Itraconazole (ITZ). Although Hydroxy Itraconazole is also reported to have antifungal activity in vitro, its pharmacokinetics in humans has been studied less than that of ITZ. ITZ and Hydroxy Itraconazole have a triazole ring and inhibit CYP3A. Their half-lives can be extended by 26-60% with repeated administration compared to single administration. In Vivo: The plasma concentration of Hydroxy Itraconazole is weakly dependent on the dose of ITZ, most likely because the process that forms Hydroxy Itraconazole is saturated. Serum albumin and GFR may alter the pharmacokinetics of ITZ and Hydroxy Itraconazole. Antifungal activity should be discussed while taking into account not only the plasma concentration of ITZ but also that of Hydroxy Itraconazole. However, the pharmacokinetics of Hydroxy Itraconazole is similar to that of ITZ in immunocompromised patients taking an oral solution of ITZ. Since the plasma concentrations of ITZ and Hydroxy Itraconazole are closely correlated, determining the plasma concentration of either should be sufficient from a clinical point of view.