The importance of CYP2C19 genotype in tacrolimus dose optimization when concomitant with voriconazole in heart transplant recipients

Aims Voriconazole remains the mainstay for the treatment of invasive fungal infections in heart transplant patients and can significantly increase tacrolimus exposure because of drug‐drug interaction (DDI). However, the magnitude of this DDI is highly variable and difficult to predict. The purpose of this study was to present the characteristics of the DDI between tacrolimus and voriconazole, and further identify the various predictors of tacrolimus dose modification. Methods We retrospectively enrolled 69 heart transplant recipients who did not use voriconazole as the control and 68 patients received voriconazole treatment in voriconazole group. CYP3A4*1G , CYP3A5 *3 and CYP2C19*2 or *3 were thereafter genotyped by Sanger sequencing. The dose of tacrolimus required to achieve the therapeutic concentrations and tacrolimus dose‐corrected trough concentration ( C 0 / D ) before and after VRC administration was evaluated. Results The DDI between tacrolimus and voriconazole displayed a large interindividual variability with more than 10‐fold changes in tacrolimus dose (range 1.28‐13.00) and C 0 /D (range 1.43‐13.75). In addition, the fold changes for the tacrolimus dose were associated with CYP2C19 genotype, which was found to be significantly lower in CYP2C19 extensive metabolizers than in CYP2C19 intermediate metabolizers or poor metabolizers (4.06 ± 1.85 vs 5.49 ± 2.47, P = .0031). However, no significant difference was found in both CYP3A4 and CYP3A5 genotypes. Moreover, CYP2C19 genotype and hematocrit acted as independent predicting factors for tacrolimus dose modification after voriconazole co‐therapy. Conclusions The findings of this study have identified the various important factors to adjust tacrolimus dosage when co‐administrated with voriconazole in individual patients. CYP2C19 genotype and haematocrit should be considered when tailoring tacrolimus dose.