12 CLINICAL PHARMACOLOGY

12.1 Mechanism of Action

PREVYMIS is an antiviral drug against CMV [see Microbiology (12.4)].

12.2 Pharmacodynamics

Cardiac Electrophysiology

In a thorough QT trial in healthy adult subjects, letermovir at the therapeutic IV dose or at a dose of 2 times the approved IV dose did not prolong QTc to any clinically relevant extent.

12.3 Pharmacokinetics

The pharmacokinetic properties of letermovir are displayed in Table 12.

Table 12: Absorption, Distribution, Metabolism, Elimination (ADME), and Pharmacokinetic Properties of PREVYMIS*
* Values were obtained in studies of healthy adult subjects unless otherwise indicated. † Based on geometric mean data. ‡ 95% CI (46%, 65%) § Values refer to geometric mean ratio [fed/fasted] percentage and 90% confidence interval back transformed from linear mixed-effects model performed on natural log-transformed values. The meal administered was a standard high fat and high calorie meal (33 grams protein, 65 grams carbohydrates, 58 grams fat; 920 total calories). ¶ Single oral administration of radiolabeled letermovir in mass balance study.
Pharmacokinetics in Adult HSCT Recipients
Treatment Regimen	Steady-state median (90% prediction interval) AUC (ng∙hr/mL) of PREVYMIS
480 mg oral once daily, no cyclosporine	34,400 (16,900, 73,700)
480 mg IV once daily, no cyclosporine	100,000 (65,300, 148,000)
240 mg oral once daily, with cyclosporine	60,800 (28,700, 122,000)
240 mg IV once daily, with cyclosporine	70,300 (46,200, 106,000)
Pharmacokinetics in Adult Kidney Transplant Recipients
Treatment Regimen	Steady-state median (90% prediction interval) AUC (ng∙hr/mL) of PREVYMIS
480 mg oral once daily, no cyclosporine	62,700 (17,500, 139,000)
240 mg oral once daily, with cyclosporine	71,900 (42,400, 125,000)
Pharmacokinetics in Adult Healthy Subjects
Treatment Regimen	Steady-state geometric mean AUC and Cmax of PREVYMIS
480 mg oral once daily	Cmax: 13,000 ng/mL
	AUC: 71,500 ng•hr/mL
Dose proportionality	Greater than proportional following single and multiple oral or IV doses of PREVYMIS 240 mg and 480 mg
Accumulation ratio†	Cmax: 1.03 AUC: 1.22
Time to steady-state	9-10 days
Absorption
Bioavailability	Healthy adult subjects administered PREVYMIS without cyclosporine: 94% at an oral dose range of 240 mg to 480 mg Adult HSCT recipients administered PREVYMIS without cyclosporine: 35% with 480 mg oral once daily Adult HSCT recipients administered PREVYMIS with cyclosporine: 85% with 240 mg oral once daily Adult kidney transplant recipients administered PREVYMIS without cyclosporine: 56%‡ with 480 mg oral once daily
Median Tmax (hr)	1.5 to 3.0 hr
Effect of food (relative to fasting)§	AUC: 99.63% [84.27% - 117.80%] Cmax: 129.82% [104.35% -161.50%]
Oral pellets versus tablet (fasting)	AUC and Cmax values were comparable when comparing PREVYMIS tablet (240 mg) and PREVYMIS oral pellets (2 X 120 mg)
Distribution
Mean steady-state volume of distribution	45.5 L following IV administration in adult HSCT recipients
% In vitro bound to human plasma proteins	99% across the concentration range of 0.2 to 50 mg/L
In vitro blood-to plasma ratio	0.56 across the concentration range of 0.1 to 10 mg/L
Metabolism
In vitro metabolism	UGT1A1/1A3 (minor)
Drug-related component in plasma	97% unchanged parent No major metabolites detected in plasma
Elimination
Route of elimination	Hepatic uptake (OATP1B1/3)
Mean terminal t1/2 (hr)	12 hrs after dosing of PREVYMIS 480 mg IV once daily
% of dose excreted in feces¶	93%
% of dose excreted in urine¶	<2%
% of unchanged drug excreted in feces¶	70%

Specific Populations

Pediatric Patients

Letermovir AUC in pediatric HSCT recipients was estimated using population pharmacokinetic analysis using Trial P030 data (see Table 13 and Table 14). Exposures for pediatric HSCT recipients for body weight bands 6 kg and above are within the range of exposures observed at the recommended doses of PREVYMIS in adults (see Table 12).

Table 13: PREVYMIS AUC (ng•hr/mL) Values Following Once Daily Oral Administration in Pediatric HSCT Recipients
Body Weight	Oral Dose, No Cyclosporine	Steady-state Median (90% Prediction Interval)*	Oral Dose, With Cyclosporine	Steady-state Median (90% Prediction Interval)*
* Medians and 90% prediction intervals are based on simulations using the pediatric HSCT population PK model with inter-individual variability. † Includes pediatric patients 12 years of age and older or weighing ≥ 30 kg. ‡ Includes pediatric patients 6 months of age and older and weighing 6 kg to < 7.5 kg.
30 kg and above†	480 mg	38,500 (18,100, 78,100)	240 mg	50,200 (24,100, 102,000)
15 kg to less than 30 kg	240 mg	39,600 (21,300, 71,800)	120 mg	53,200 (27,800, 102,000)
7.5 kg to less than 15 kg	120 mg	32,900 (16,800, 61,200)	60 mg	42,300 (22,300, 81,500)
6 kg to less than 7.5 kg‡	80 mg	29,400 (16,600, 54,100)	40 mg	39,200 (20,900, 71,800)

Table 14: PREVYMIS AUC (ng•hr/mL) Values Following Once Daily IV Administration in Pediatric HSCT Recipients
Body Weight	IV Dose, No Cyclosporine	Steady-state Median (90% Prediction Interval)*	IV Dose, With Cyclosporine	Steady-state Median (90% Prediction Interval)*
* Medians and 90% prediction intervals are based on simulations using the pediatric HSCT population PK model with inter-individual variability. † Includes pediatric patients 12 years of age and older or weighing ≥ 30 kg. ‡ Includes pediatric patients 6 months of age and older and weighing 6 kg to < 7.5 kg.
30 kg and above†	480 mg	114,000 (53,900, 230,000)	240 mg	61,400 (29,300, 128,000)
15 kg to less than 30 kg	120 mg	56,400 (29,100, 110,000)	120 mg	62,300 (32,100, 114,000)
7.5 kg to less than 15 kg	60 mg	45,900 (24,500, 86,400)	60 mg	49,900 (26,300, 96,300)
6 kg to less than 7.5 kg‡	40 mg	42,800 (23,800, 79,200)	40 mg	46,400 (26,300, 86,500)

Age, Gender, Race, and Weight

Age (18 to 82 years), gender, race, and body weight (up to 100 kg) did not have a clinically significant effect on the pharmacokinetics of letermovir in adult subjects.

Renal Impairment

Clinical Study in a Renally Impaired Population

Letermovir AUC was approximately 1.9- and 1.4-fold higher in adult subjects with moderate (eGFR greater than or equal to 30 to 59 mL/min/1.73m2) and severe (eGFR less than 30 mL/min/1.73m2) renal impairment, respectively, compared to healthy adult subjects.

Post-kidney Transplant

Based on population pharmacokinetic analysis, letermovir AUC was approximately 1.1-, 1.3- and 1.4-fold higher in adult subjects with mild (CLcr greater than or equal to 60 to less than 90 mL/min), moderate (CLcr greater than or equal to 30 to less than 60 mL/min) and severe (CLcr greater than or equal to 15 to less than 30 mL/min) renal impairment, respectively, compared to adult subjects with CLcr greater than or equal to 90 mL/min.

Intravenous Formulation

Hydroxypropyl betadex present in the intravenous letermovir formulation is mainly eliminated by glomerular filtration. Decreased elimination of hydroxypropyl betadex has been reported in the literature in patients with severe renal impairment.

Hepatic Impairment

Letermovir AUC was approximately 1.6- and 3.8-fold higher in adult subjects with moderate (Child-Pugh Class B [CP-B], score of 7-9) and severe (Child-Pugh Class C [CP-C], score of 10-15) hepatic impairment, respectively, compared to healthy adult subjects.

Drug Interaction Studies

Drug interaction studies were performed in healthy adult subjects with PREVYMIS and drugs likely to be co-administered or drugs commonly used as probes for pharmacokinetic interactions (see Table 15 and Table 16).

In vitro results indicate that letermovir is a substrate of drug metabolizing enzymes CYP3A, CYP2D6, UGT1A1, and UGT1A3, and transporters OATP1B1/3 and P-gp. Oxidative metabolism is considered to be a minor elimination pathway based on in vivo human data. Inhibitors of OATP1B1/3 may result in increases in letermovir plasma concentrations. Changes in letermovir plasma concentrations due to inhibition of P-gp/BCRP by itraconazole were not clinically relevant. Changes in letermovir plasma concentrations due to inhibition of UGTs are not anticipated to be clinically relevant.

Based on in vitro studies, the metabolism of letermovir is not mediated by CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2E1, CYP4A11, UGT1A4, UGT1A6, UGT1A7, UGT1A8, UGT1A9, UGT1A10, UGT2B4, UGT2B7, UGT2B15, or UGT2B17. The transport of letermovir is not mediated by OATP2B1, OCT1, OAT1, BCRP, or MRP2 in vitro.

Letermovir is a time-dependent inhibitor and inducer of CYP3A in vitro. Co-administration of PREVYMIS with midazolam resulted in increased exposure of midazolam, indicating that the net effect of letermovir on CYP3A is moderate inhibition (see Table 16). Based on these results, co-administration of PREVYMIS with CYP3A substrates may increase the plasma concentrations of the CYP3A substrates [see Contraindications (4), Warnings and Precautions (5.1), Drug Interactions (7.2, 7.3), and Table 11]. Letermovir is a reversible inhibitor of CYP2C8 in vitro. When co-administered with PREVYMIS, plasma concentrations of CYP2C8 substrates are predicted to be increased [see Table 11 in Drug Interactions (7.3)]. Co-administration of PREVYMIS reduced the exposure of voriconazole, most likely due to the induction of voriconazole elimination pathways, CYP2C9 and CYP2C19. Co-administration of PREVYMIS with CYP2C9 and CYP2C19 substrates may decrease the plasma concentrations of the CYP2C9 and CYP2C19 substrates [see Table 11 in Drug Interactions (7.3)]. Letermovir is an inducer of CYP2B6 in vitro; the clinical relevance is unknown.

Letermovir inhibited efflux transporters P-gp, breast cancer resistance protein (BCRP), bile salt export pump (BSEP), multidrug resistance-associated protein 2 (MRP2), OAT3, and hepatic uptake transporter OATP1B1/3 in vitro. Co-administration of PREVYMIS with substrates of OATP1B1/3 transporters (e.g., atorvastatin, a known substrate of CYP3A, OATP1B1/3, and potentially BCRP) may result in a clinically relevant increase in plasma concentrations of OATP1B1/3 substrates [see Table 11 in Drug Interactions (7.3)]. There were no clinically relevant changes in plasma concentrations of digoxin, a P-gp substrate, or acyclovir, an OAT3 substrate, following co-administration with PREVYMIS in clinical studies (see Table 16). The effect of letermovir on BCRP, BSEP, and MRP2 substrates was not evaluated in clinical studies; the clinical relevance is unknown.

Based on in vitro results letermovir is not an inhibitor of CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, UGT1A4, UGT1A6, UGT1A9, or UGT2B7 and is not an inducer of CYP1A2. Letermovir is not an inhibitor of OATP2B1, OCT1, OCT2, or OAT1 in vitro.

Table 15: Drug Interactions: Changes in Pharmacokinetics of Letermovir in the Presence of Co-administered Drug
Co-administered Drug	Regimen of Co-administered Drug	Letermovir Regimen	Geometric Mean Ratio [90% CI] of Letermovir PK with/without Co-administered Drug (No Effect=1.00)
Co-administered Drug	Regimen of Co-administered Drug	Letermovir Regimen	AUC	Cmax	C24hr*
Abbreviations: PO= oral
* C12hr for tacrolimus † These data are the effect of rifampin on letermovir 24 hours after final rifampin dose.
Antifungals
fluconazole	400 mg single dose PO	480 mg single dose PO	1.11 (1.01, 1.23)	1.06 (0.93, 1.21)	1.28 (1.15, 1.43)
itraconazole	200 mg once daily PO	480 mg once daily PO	1.33 (1.17, 1.51)	1.21 (1.05, 1.39)	1.90 (1.58, 2.28)
Antimycobacterials
rifampin	600 mg single dose PO	480 mg single dose PO	2.03 (1.84, 2.26)	1.59 (1.46, 1.74)	2.01 (1.59, 2.54)
	600 mg single dose IV	480 mg single dose PO	1.58 (1.38, 1.81)	1.37 (1.16, 1.61)	0.78 (0.65, 0.93)
	600 mg once daily PO	480 mg once daily PO	0.81 (0.67, 0.98)	1.01 (0.79, 1.28)	0.14 (0.11, 0.19)
	600 mg once daily PO (24 hours after rifampin)†	480 mg once daily PO	0.15 (0.13, 0.17)	0.27 (0.22, 0.31)	0.09 (0.06, 0.12)
Immunosuppressants
cyclosporine	200 mg single dose PO	240 mg once daily PO	2.11 (1.97, 2.26)	1.48 (1.33, 1.65)	2.06 (1.81, 2.35)
mycophenolate mofetil	1 g single dose PO	480 mg once daily PO	1.18 (1.04, 1.32)	1.11 (0.92, 1.34)	1.39 (1.12, 1.74)
tacrolimus	5 mg single dose PO	80 mg twice daily PO	1.02 (0.97, 1.07)	0.92 (0.84, 1.00)	1.02 (0.93, 1.12)

Table 16: Drug Interactions: Changes in Pharmacokinetics for Co-administered Drug in the Presence of Letermovir
Co-administered Drug	Regimen of Co-administered Drug	Letermovir Regimen	Geometric Mean Ratio [90% CI] of Co-administered Drug PK with/without Letermovir (No Effect=1.00)
Co-administered Drug	Regimen of Co-administered Drug	Letermovir Regimen	AUC	Cmax	C24hr*
Abbreviations: PO=oral
* C12hr reported for voriconazole.
CYP3A Substrates
midazolam	1 mg single dose IV	240 mg once daily PO	1.47 (1.37, 1.58)	1.05 (0.94, 1.17)	2.74 (2.16, 3.49)
midazolam	2 mg single dose PO	240 mg once daily PO	2.25 (2.04, 2.48)	1.72 (1.55, 1.92)	Not available
P-gp Substrates
digoxin	0.5 mg single dose PO	240 mg twice daily PO	0.88 (0.80, 0.96)	0.75 (0.63, 0.89)	0.90 (0.84, 0.96)
Immunosuppressants
cyclosporine	50 mg single dose PO	240 mg once daily PO	1.66 (1.51, 1.82)	1.08 (0.97, 1.19)	2.19 (1.80, 2.66)
mycophenolate mofetil	1 g single dose PO	480 mg once daily PO	1.08 (0.97, 1.20)	0.96 (0.82, 1.12)	1.04 (0.86, 1.27)
tacrolimus	5 mg single dose PO	480 mg once daily PO	2.42 (2.04, 2.88)	1.57 (1.32, 1.86)	2.53 (2.12, 3.03)
sirolimus	2 mg single dose PO	480 mg once daily PO	3.40 (3.01, 3.85)	2.76 (2.48, 3.06)	3.15 (2.80, 3.55)
Antifungals and Antivirals
acyclovir	400 mg single dose PO	480 mg once daily PO	1.02 (0.87, 1.2)	0.82 (0.71, 0.93)	1.13 (0.94, 1.36)
fluconazole	400 mg single dose PO	480 mg single dose PO	1.03 (0.99, 1.08)	0.95 (0.92, 0.99)	1.04 (1.00, 1.08)
itraconazole	200 mg once daily PO	480 mg once daily PO	0.76 (0.71, 0.81)	0.84 (0.76, 0.92)	0.67 (0.61, 0.73)
posaconazole	300 mg single dose PO	480 mg once daily PO	0.98 (0.82, 1.17)	1.11 (0.95, 1.29)	1.10 (0.94, 1.30)
voriconazole	200 mg twice daily PO	480 mg once daily PO	0.56 (0.51, 0.62)	0.61 (0.53, 0.71)	0.49 (0.42, 0.57)
HMG-CoA Reductase Inhibitors
atorvastatin	20 mg single dose PO	480 mg once daily PO	3.29 (2.84, 3.82)	2.17 (1.76, 2.67)	3.62 (2.87, 4.55)
Oral Contraceptives
ethinyl estradiol (EE) /levonorgestrel (LNG)	0.03 mg EE single dose PO	480 mg once daily PO	1.42 (1.32, 1.52)	0.89 (0.83, 0.96)	1.57 (1.45, 1.70)
ethinyl estradiol (EE) /levonorgestrel (LNG)	0.15 mg LNG single dose PO	480 mg once daily PO	1.36 (1.30, 1.43)	0.95 (0.86, 1.04)	1.38 (1.32, 1.46)

12.4 Microbiology

Mechanism of Action

Letermovir inhibits the CMV DNA terminase complex (pUL51, pUL56, and pUL89) which is required for viral DNA processing and packaging. Biochemical characterization and electron microscopy demonstrated that letermovir affects the production of proper unit length genomes and interferes with virion maturation. Genotypic characterization of virus resistant to letermovir confirmed that letermovir targets the terminase complex.

Antiviral Activity

The median EC50 value of letermovir against a collection of clinical CMV isolates in a cell-culture model of infection was 2.1 nM (range = 0.7 nM to 6.1 nM, n = 74). There was no significant difference in EC50 value by CMV gB genotype (gB1=29; gB2=27; gB3=11; and gB4=3).

Combination Antiviral Activity

No antagonism of the antiviral activity was seen when letermovir was combined with CMV DNA polymerase inhibitors (cidofovir, foscarnet, or ganciclovir).

Viral Resistance

In Cell Culture

CMV mutants with reduced susceptibility to letermovir have been selected in cell culture and the resistance mutations map to UL51, UL56, and UL89. Resistance-associated substitutions were found in pUL51 (P91S, A95V), pUL56 (C25F, S229F, V231A/L, N232Y, V236A/L/M, E237D, L241P, T244K/R, L254F, L257F/I, K258E, F261C/L/S, Y321C, C325F/R/W/Y, L328V, M329T, A365S, N368D, R369G/M/S), and pUL89 (N320H, D344E). EC50 values for recombinant CMV mutants expressing these substitutions are 1.6- to 9,300-fold higher than those for the wild-type reference virus.

In Clinical Studies

In a Phase 2b trial evaluating letermovir or placebo in 131 adult HSCT recipients, DNA sequence analysis of a select region of UL56 (amino acids 231 to 369) was performed on samples obtained from 12 letermovir-treated subjects who experienced prophylaxis failure and for whom on-treatment samples were available for analysis. One subject had a letermovir resistance substitution, pUL56 V236M (19-50-fold reduction in susceptibility).

In a Phase 3 trial (P001), DNA sequence analysis of the entire coding regions of UL56 and UL89 was performed on samples obtained from 50 letermovir-treated adult subjects who had received at least one dose of study drug and experienced prophylaxis failure and for whom samples were available for analysis. The pUL56 substitutions V236M (19-50-fold reduction), E237G (13-fold reduction), C325W (9300-fold reduction), and R369T (52-fold reduction) were detected in 3 subjects; however, no 2 subjects had substitutions at the same positions.

In a Phase 3 trial (P040), DNA sequence analysis of the entire coding regions of UL51, UL56 and UL89 was performed on samples obtained from 32 adult subjects (regardless of treatment group) who experienced prophylaxis failure or who discontinued early with CMV viremia. No letermovir resistance-associated substitutions were detected above the validated assay limit.

In a Phase 3 trial (P002), DNA sequence analysis of the entire coding regions of UL51, UL56 and UL89 was performed on samples obtained from 52 letermovir-treated adult subjects who experienced CMV disease or who discontinued early with CMV viremia. No previously characterized resistance-associated substitutions were identified. Novel substitutions were detected in letermovir-treated subjects at resistance-associated positions (pUL56 S229Y [2-fold reduction; n=1] and pUL56 M329I [0.77-fold reduction; n=9]) at low frequencies, ranging between 0.05 to 0.07.

In a Phase 2b trial (P030), DNA sequence analysis of the entire coding regions of UL51, UL56 and UL89 was performed on samples obtained from 10 letermovir-treated pediatric subjects at a visit for evaluation of CMV infection. A total of 2 letermovir resistance-associated substitutions both mapping to pUL56 were detected in 2 subjects. One subject had the substitution C325W (9300-fold reduction), and the other had R369S (38-fold reduction).

Cross Resistance

Cross resistance is not likely with drugs outside of this class. Letermovir is fully active against viral populations with substitutions conferring resistance to CMV DNA polymerase inhibitors (cidofovir, foscarnet, and ganciclovir). These DNA polymerase inhibitors are expected to be fully active against viral populations with substitutions conferring resistance to letermovir.