CYP3A4 and immunodeficiency disease: In other words, antifungal therapy with posaconazole, the second generation of triazole antifungal agent, significantly reduced clearance of sirolimus in children with PIK3CD mutation-related immunodeficiency disease, because posaconazole is an inhibitor of the cytochrome P450 (CYP) isoenzyme CYP3A4, and sirolimus is a substrate of the enzyme (Moton et al., 2009).