Letermovir (AIC246, MK‐8228) is a human cytomegalovirus terminase inhibitor indicated for the prophylaxis of cytomegalovirus infection and disease in allogeneic hematopoietic stem cell transplant recipients that is also being investigated for use in other transplant settings. Many transplant patients receive immunosuppressant drugs, of which several have narrow therapeutic ranges. There is a potential for the coadministration of letermovir with these agents, and any potential effect on their pharmacokinetics (PK) must be understood. Five phase 1 trials were conducted in 73 healthy female participants to evaluate the effect of letermovir on the PK of cyclosporine, tacrolimus, sirolimus, and mycophenolic acid (active metabolite of mycophenolate mofetil [MMF]), as well as the effect of cyclosporine and MMF on letermovir PK. Safety and tolerability were also assessed. Coadministration of letermovir with cyclosporine, tacrolimus, and sirolimus resulted in 1.7‐, 2.4‐, and 3.4‐fold increases in area under the plasma concentration–time curve and 1.1‐, 1.6‐, and 2.8‐fold increases in maximum plasma concentration, respectively, of the immunosuppressants. Coadministration of letermovir and MMF had no meaningful effect on the PK of mycophenolic acid. Coadministration with cyclosporine increased letermovir area under the plasma concentration–time curve by 2.1‐fold and maximum plasma concentration by 1.5‐fold, while coadministration with MMF did not meaningfully affect the PK of letermovir. Given the increased exposures of cyclosporine, tacrolimus, and sirolimus, frequent monitoring of concentrations should be performed during administration and at discontinuation of letermovir, with dose adjustment as needed. These data support the reduction in clinical dosage of letermovir (to 240 mg) upon coadministration with cyclosporine.
Background:
Letermovir is approved for prophylaxis of cytomegalovirus infection and disease in cytomegalovirus-seropositive hematopoietic stem-cell transplant (HSCT) recipients.
Objective:
HSCT recipients are required to take many drugs concomitantly. The pharmacokinetics, absorption, distribution, metabolism, and excretion of letermovir and its potential to inhibit metabolizing enzymes and transporters In vitro were investigated to inform on the potential for drug‒drug interactions (DDIs).
Methods:
A combination of in vitro and in vivo studies described the absorption, distribution, metabolism, and routes of elimination of letermovir, as well as the enzymes and transporters involved in these processes. The effect of letermovir to inhibit and induce metabolizing enzymes and transporters were evaluated In vitro and its victim and perpetrator DDI potentials were predicted by applying the regulatory guidance for DDI assessment.
Results:
Letermovir was a substrate of CYP3A4/5 and UGT1A1/3 in vitro. Letermovir showed concentration-dependent uptake into organic anionic transporting polypeptide (OATP)1B1/3-transfected cells and was a substrate of P-glycoprotein (P-gp). In a human ADME study, letermovir was primarily recovered as unchanged drug and minor amounts of a direct glucuronide in feces. Based on the metabolic pathway profiling of letermovir, there were few oxidative metabolites in human matrix. Letermovir inhibited CYP2B6, CYP2C8, CYP3A, and UGT1A1 in vitro, and induced CYP3A4 and CYP2B6 in hepatocytes. Letermovir also inhibited OATP1B1/3, OATP2B1, OAT3, OCT2, BCRP, BSEP, and P-gp.
Conclusion:
The body of work presented in this manuscript informed on the potential for DDIs when letermovir is administered both intravenously and orally in HSCT recipients.
As rifampicin can cause the induction and inhibition of multiple metabolizing enzymes and transporters, it has been challenging to accurately predict the complex drug–drug interactions (DDIs). We previously constructed a physiologically‐based pharmacokinetic (PBPK) model of rifampicin accounting for the components for the induction of cytochrome P450 (CYP) 3A/CYP2C9 and the inhibition of organic anion transporting polypeptide 1B (OATP1B). This study aimed to expand and verify the PBPK model for rifampicin by incorporating additional components for the induction of OATP1B and CYP2C8 and the inhibition of multidrug resistance protein 2. The established PBPK model was capable of accurately predicting complex rifampicin‐induced alterations in the profiles of glibenclamide, repaglinide, and coproporphyrin I (an endogenous biomarker of OATP1B activities) with various dosing regimens. Our comprehensive rifampicin PBPK model may enable quantitative prediction of DDIs across diverse potential victim drugs and endogenous biomarkers handled by multiple metabolizing enzymes and transporters.
This communication describes a significant expansion in the scope of Stille reactions of Csp3-X electrophiles, specifically, that Pd/P(t-Bu)2Me catalyzes the room-temperature cross-coupling of a variety of functionalized, beta-hydrogen-containing alkyl bromides with an array of alkenyltin reagents. The structure of the phosphine (P(t-Bu)2Me) is well suited for facilitating oxidative addition and avoiding beta-hydride elimination, while the fluoride serves to activate the tin reagent for efficient transmetalation.
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