Decrease in voriconazole concentration-to-dose ratio after letermovir initiation: a retrospective, observational study.

Letermovir is used to prevent cytomegalovirus infection in hematopoietic stem cell transplantation (HSCT) recipients. Although this agent decreases voriconazole exposure in healthy individuals, the effect of coadministration of letermovir and voriconazole in HSCT recipients is unknown. This retrospective, observational, single-center study was conducted between January 2016 and July 2019 to examine the voriconazole concentration-to-dose ratio over three periods: (A) (days -7 to -1 [day 0: day of HCST]), (B) (days 4-10), and (C) (days 11-17). Forty-two HSCT recipients administered voriconazole were divided into the following two groups based on letermovir coadministration: letermovir (n = 15) and control (n = 27). The percent change (-33.2%, p < 0.05) in the voriconazole concentration-to-dose ratio from periods A to C in the letermovir group was significantly lower than that in the control group. Therefore, frequent therapeutic drug monitoring of voriconazole concentrations and subsequent dose adjustments should be performed regularly in HSCT recipients.

Tacrolimus Concentration after Letermovir Initiation in Hematopoietic Stem Cell Transplantation Recipients Receiving Voriconazole: A Retrospective, Observational Study.

Letermovir (LMV) is a new antiviral drug used to prevent cytomegalovirus infection in hematopoietic stem cell transplantation (HSCT) recipients. It has been reported to increase tacrolimus (TAC) exposure and decrease voriconazole (VRCZ) exposure in healthy participants. However, VRCZ inhibits the metabolism of TAC. Thus, the effects of LMV on TAC exposure in patients receiving VRCZ are unknown. This retrospective, observational, single-center study was conducted between May 2018 and April 2019. The TAC concentration/dose (C/D) ratio, VRCZ concentration, and VRCZ C/D ratio for 7 days before and for the first and second 7-day periods after the initiation of LMV administration were evaluated. Fourteen HSCT recipients receiving VRCZ were enrolled. There was no significant difference in the TAC C/D ratio for 7 days before and for the first and second 7-day periods after initiating LMV administration (median: 866 [IQR: 653-953], 842 [IQR: 636-1031], and 906 [IQR: 824-1210] [ng/mL]/[mg/kg], respectively). In contrast, the VRCZ C/D ratio and concentration for the first and second 7-day periods after LMV initiation were significantly lower than those before initiating LMV administration (mean 1.11 ± 0.07, 0.12 ± 0.08, and 0.22 ± 0.12 [µg/mL]/[mg/kg] and 0.7 ± 0.5, 0.8 ± 0.5, and 1.3 ± 0.7 µg/mL, respectively; n = 12). This can be explained by the increase in TAC concentration caused by CYP3A4 inhibition due to LMV and by the decrease in TAC concentration ascribed to the decrease in VRCZ concentration by CYP2C19 induction due to LMV. These results suggest that it is unnecessary to adjust the dose of TAC based on LMV initiation; however, it is necessary to adjust the dose of TAC based on conventional TAC concentration measurements.