Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1    Pharmacodynamic properties

Pharmacotherapeutic group: Antivirals for systemic use; Direct acting antiviral, ATC code: J05AP55 
Mechanism of action

Sofosbuvir is a pan-genotypic inhibitor of the HCV NS5B RNA-dependent RNA polymerase, which is essential for viral replication. Sofosbuvir is a nucleotide prodrug that undergoes intracellular metabolism to form the pharmacologically active uridine analogue triphosphate (GS-461203), which can be incorporated into HCV RNA by the NS5B polymerase and acts as a chain terminator.
GS-461203 (the active metabolite of sofosbuvir) is neither an inhibitor of human DNA and RNA polymerases nor an inhibitor of mitochondrial RNA polymerase.

Velpatasvir is a HCV inhibitor targeting the HCV NS5A protein, which is essential for both RNA replication and the assembly of HCV virions. In vitro resistance selection and cross-resistance studies indicate velpatasvir targets NS5A as its mode of action.

Antiviral activity

The 50% effective concentration (EC50) values of sofosbuvir and velpatasvir against full-length or chimeric replicons encoding NS5B and NS5A sequences from the laboratory strains are presented in Table 5. The EC50 values of sofosbuvir and velpatasvir against clinical isolates are presented in Table 6.

Table 5: Activity of sofosbuvir and velpatasvir against full-length or chimeric laboratory replicons
Replicon genotype         Sofosbuvir EC50, nMa         Velpatasvir EC50, nMa 1a                        40                           0.014
1b                        110                          0.016
2a                        50                           0.005-0.016c
2b                        15b                          0.002-0.006c
3a                        50                           0.004
4a                        40                           0.009
4d                        NA                           0.004
5a                        15b                          0.021-0.054d
6a                        14b                          0.006-0.009
6e                        NA                           0.130d
NA = Not available a Mean value from multiple experiments of same laboratory replicon.
b Stable chimeric 1b replicons carrying NS5B genes from genotype 2b, 5a or 6a were used for testing.
c Data from various strains of full length NS5A replicons or chimeric NS5A replicons carrying full-length NS5A genes that contain L31 or M31 polymorphisms.
d Data from a chimeric NS5A replicon carrying NS5A amino acids 9-184.

Table 6: Activity of sofosbuvir and velpatasvir against transient replicons containing NS5A or NS5B from clinical isolates
Replicon        Replicons containing NS5B from clinical              Replicons containing NS5A from clinical genotype        isolates                                             isolates Number of clinical    Median sofosbuvir              Number of clinical Median velpatasvir isolates              EC50, nM (range)               isolates             EC50, nM (range) 1a              67                    62 (29-128)                    23                   0.019 (0.011-0.078) 1b              29                    102 (45-170)                   34                   0.012 (0.005-0.500) 2a              15                    29 (14-81)                     8                    0.011 (0.006-0.364)
2b              NA                    NA                             16                   0.002 (0.0003-0.007)
3a              106                   81 (24-181)                    38                   0.005 (0.002-1.871) 4a              NA                    NA                             5                    0.002 (0.001-0.004)
4d              NA                    NA                             10                   0.007 (0.004-0.011)
4r              NA                    NA                             7                    0.003 (0.002-0.006)
5a              NA                    NA                             42                   0.005 (0.001-0.019) 6a              NA                    NA                             26                   0.007 (0.0005-0.113) 6e              NA                    NA                             15                   0.024 (0.005-0.433) NA = Not available

The presence of 40% human serum had no effect on the anti-HCV activity of sofosbuvir but reduced the anti-HCV activity of velpatasvir by 13-fold against genotype 1a HCV replicons.

Evaluation of sofosbuvir in combination with velpatasvir showed no antagonistic effect in reducing HCV RNA levels in replicon cells.
Resistance

In cell culture
HCV replicons with reduced susceptibility to sofosbuvir have been selected in cell culture for multiple genotypes including 1b, 2a, 2b, 3a, 4a, 5a and 6a. Reduced susceptibility to sofosbuvir was associated with the primary NS5B substitution S282T in all replicon genotypes examined. Site-directed mutagenesis of the S282T substitution in replicons of genotype 1 to 6 conferred 2- to 18-fold reduced susceptibility to sofosbuvir and reduced the replication viral capacity by 89% to 99% compared to the corresponding wild-type. In biochemical assays, the ability of the active triphosphate of sofosbuvir (GS-461203) to inhibit recombinant NS5B polymerase from genotypes 1b, 2a, 3a and 4a expressing the S282T substitution was reduced compared to its ability to inhibit wild-type recombinant NS5B polymerase, as indicated by a 8.5- to 24-fold increase in the 50% inhibitory concentration (IC50).

In vitro selection of HCV replicons with reduced susceptibility to velpatasvir was performed in cell culture for multiple genotypes including 1a, 1b, 2a, 3a, 4a, 5a and 6a. Variants were selected at NS5A resistance associated positions 24, 28, 30, 31, 32, 58, 92 and 93. The resistance associated variants (RAVs) selected in 2 or more genotypes were F28S, L31I/V and Y93H. Site-directed mutagenesis of known NS5A RAVs showed that substitutions conferring a > 100-fold reduction in velpatasvir susceptibility are M28G, A92K and Y93H/N/R/W in genotype 1a, A92K in genotype 1b, C92T and Y93H/N in genotype 2b, Y93H in genotype 3, and L31V and P32A/L/Q/R in genotype 6. No individual substitutions tested in genotypes 2a, 4a, or 5a conferred a > 100-fold reduction in velpatasvir susceptibility. Combinations of these variants often showed greater reductions in susceptibility to velpatasvir than single RAVs alone.

In clinical studies
Studies in patients without cirrhosis and patients with compensated cirrhosis In a pooled analysis of patients without cirrhosis or with compensated cirrhosis who received Epclusa for 12 weeks in three Phase 3 studies, 12 patients (2 with genotype 1 and 10 with genotype 3) qualified for resistance analysis due to virologic failure. One additional patient with genotype 3 HCV infection at baseline was reinfected with genotype 1a HCV at virologic failure and was excluded from the virological analysis. No patients with genotype 2, 4, 5, or 6 HCV infection experienced virologic failure.

Of the 2 genotype 1 virologic failure patients, one patient had virus with emergent NS5A RAV Y93N and the other patient had virus with emergent NS5A RAVs L31I/V and Y93H at virologic failure.
Both patients had virus at baseline harbouring NS5A RAVs. No NS5B nucleoside inhibitor (NI) RAVs were observed at failure in the 2 patients.

Of the 10 genotype 3 virologic failure patients, Y93H was observed in all 10 patients at failure (6 had Y93H emerge post-treatment and 4 patients had Y93H at baseline and post-treatment). No NS5B NI RAVs were observed at failure in the 10 patients.

Studies in patients with decompensated cirrhosis
In one Phase 3 study in patients with decompensated cirrhosis who received Epclusa + RBV for 12 weeks, 3 patients (1 with genotype 1 and 2 with genotype 3) qualified for resistance analysis due to virologic failure. No patients with genotype 2 or 4 HCV infection in the Epclusa + RBV 12 weeks group experienced virologic failure.

The 1 virologic failure patient with genotype 1 HCV had no NS5A or NS5B RAVs at failure.

Of the 2 genotype 3 virologic failure patients, one had NS5A RAV Y93H emerge at failure. Another patient had virus with Y93H at baseline and virologic failure and also developed low levels (< 5%) of NS5B NI RAVs N142T and E237G at failure. Pharmacokinetic data from this patient was consistent with non-adherence to treatment.


In this study, 2 patients treated with Epclusa for 12 or 24 weeks without ribavirin had emergent NS5B S282T at low levels (< 5%) along with L159F.

Effect of baseline HCV resistance-associated variants on treatment outcome 
Studies in patients without cirrhosis and patients with compensated cirrhosis Analyses were conducted to explore the association between pre-existing baseline NS5A RAVs and treatment outcome for patients without cirrhosis or with compensated cirrhosis in three Phase 3 clinical studies (ASTRAL-1, ASTRAL-2 and ASTRAL-3). Of the 1,035 patients treated with sofosbuvir/velpatasvir in the three Phase 3 clinical studies, 1,023 patients were included in the analysis of NS5A RAVs; 7 patients were excluded as they neither achieved sustained virologic response (SVR12) nor had virologic failure and 5 additional patients were excluded as NS5A gene sequencing failed. In the pooled analysis of the Phase 3 studies, 380/1,023 (37%) patients’ virus had baseline NS5A RAVs. Genotype 2, 4, and 6 HCV-infected patients had a higher prevalence of NS5A RAVs (70%, 63% and 52%, respectively) compared to genotype 1 (23%), genotype 3 (16%), and genotype 5 (18%) HCV-infected patients.

Baseline RAVs had no relevant impact on SVR12 rates in patients infected with genotype 1, 2, 4, 5 and 6 HCV, as summarised in Table 7. Genotype 3 infected patients with the NS5A RAV Y93H at baseline had a lower SVR12 rate than patients without Y93H after treatment with Epclusa for 12 weeks, as summarised in Table 8. In the ASTRAL-3 study, the Y93H RAV was detected at baseline in 9% of patients treated with Epclusa.

Table 7: SVR12 in patients with or without baseline NS5A RAVs by HCV genotype (studies ASTRAL-1, ASTRAL-2 and ASTRAL-3)
Epclusa 12 weeks
Genotype 1         Genotype 3     Genotypes 2, 4, 5 or     Total
6
With any baseline                                                                         98% 97% (73/75)        88% (38/43)     100% (262/262)
NS5A RAVs                                                                                 (373/380) 99%
Without baseline NS5A RAVs     100% (251/251)     97% (225/231)   100% (161/161) (637/643)

Table 8: SVR12 in patients with and without baseline Y93H, 1% Cut-off (Resistance Analysis Population Set) ASTRAL 3
Epclusa 12 Weeks
All Subjects            Cirrhotic                Non-Cirrhotic
(n = 274)               (n = 80)                 (n = 197)
Overall                          95.3% (263/274)         91.3% (73/80)            97.9% (190/194) 95% CI                           92.9% to 98.0%          82.8% to 96.4%           92.8% to 98.6% SVR with Y93H                    84.0% (21/25)           50.0% (2/4)              90.5% (19/21) 95% CI                           63.9% to 95.5%          6.8% to 93.2%            69.6% to 98.8% SVR without Y93H                 96.4% (242/249)         93.4% (71/76)            98.8% (171/173) 95% CI                           94.3% to 98.9%          85.3% to 97.8%           95.9% to 99.9% 
The NS5B NI RAV S282T was not detected in the baseline NS5B sequence of any patient in Phase 3 studies. SVR12 was achieved in all 77 patients who had baseline NS5B NI RAVs including N142T, L159F, E/N237G, C/M289L/I, L320F/I/V, V321A/I, and S282G+V321I.

Studies in patients with decompensated cirrhosis (CPT Class B)
Analyses were conducted to explore the association between pre-existing baseline NS5A RAVs and treatment outcome for patients with decompensated cirrhosis in one Phase 3 study (ASTRAL-4). Of the 87 patients treated with Epclusa + RBV, 85 patients were included in the analysis of NS5A RAVs; 2 patients were excluded as they neither achieved SVR12 nor had virologic failure. Among the patients who received treatment with Epclusa + RBV for 12 weeks, 29% (25/85) of patients had baseline virus with NS5A RAVs: 29% (19/66), 75% (3/4), 15% (2/13), and 50% (1/2) for patients with genotype 1, 2, 3 and 4 HCV, respectively.

SVR12 in patients with or without baseline NS5A RAVs in the Epclusa + RBV 12 week group for this study is shown in Table 9.

Table 9: SVR12 in patients with or without baseline NS5A RAVs by HCV genotype (study ASTRAL-4)
Epclusa + RBV 12 weeks
Genotype 1         Genotype 3      Genotypes 2 or 4      Total
With any baseline
100% (19/19)       50% (1/2)         100% (4/4)          96% (24/25)
NS5A RAVs
Without baseline NS5A RAVs     98% (46/47)        91% (10/11)       100% (2/2)          98% (58/60) 
The single genotype 3 patient who had baseline NS5A RAVs and failed to achieve SVR12 had NS5A substitution Y93H at baseline; pharmacokinetic data from this patient was consistent with non-adherence to treatment.

Three patients in the Epclusa + RBV 12 week group had baseline NS5B NI RAVs (N142T and L159F) and all three patients achieved SVR12.

Paediatric population

The presence of NS5A and NS5B RAVs did not impact treatment outcome in Study 1143; all patients with baseline NS5A (n=16) or NS5B NI (n=5) RAVs achieved SVR following 12 weeks treatment with Epclusa.

Cross-resistance

In vitro data suggests that the majority of NS5A RAVs that confer resistance to ledipasvir and daclatasvir remained susceptible to velpatasvir. Velpatasvir was fully active against the sofosbuvir resistance-associated substitution S282T in NS5B while all velpatasvir resistance-associated substitutions in NS5A were fully susceptible to sofosbuvir. Both sofosbuvir and velpatasvir were fully active against substitutions associated with resistance to other classes of direct-acting antivirals with different mechanisms of actions, such as NS5B non-nucleoside inhibitors and NS3 protease inhibitors.
The efficacy of Epclusa has not been assessed in patients who have previously failed treatment with other regimens that include an NS5A inhibitor.

Clinical efficacy and safety

Adults
The efficacy of Epclusa was evaluated in three Phase 3 studies in patients with genotype 1 to 6 HCV infection with or without compensated cirrhosis, one Phase 3 study in patients with genotype 1 to 6 HCV infection with decompensated cirrhosis, one Phase 3 study in HCV/HIV-1 co-infected patients with genotype 1 to 6 HCV infection and one Phase 2 study in patients with HCV infection and ESRD requiring dialysis, as summarised in Table 10.


Table 10: Studies conducted with Epclusa in adult patients with genotype 1, 2, 3, 4, 5 or 6 HCV infection
Study                 Population                                                Study arms (Number of patients treated)
Genotype 1, 2, 4, 5 and 6
Epclusa 12 weeks (624)
ASTRAL-1              TN and TE, without cirrhosis or with
Placebo 12 weeks (116) compensated cirrhosis
Genotype 2
Epclusa 12 weeks (134)
ASTRAL-2              TN and TE, without cirrhosis or with
SOF+RBV 12 weeks (132) compensated cirrhosis
Genotype 3
Epclusa 12 weeks (277)
ASTRAL-3              TN and TE, without cirrhosis or with
SOF+RBV 24 weeks (275) compensated cirrhosis
Genotype 1, 2, 3, 4, 5 and 6                              Epclusa 12 weeks (90) ASTRAL-4              TN and TE, with CPT Class B decompensated                 Epclusa + RBV 12 weeks (87) cirrhosis                                                 Epclusa 24 weeks (90) Genotype 1, 2, 3, 4, 5 and 6
TN and TE, without cirrhosis or with
ASTRAL-5                                                                        Epclusa 12 weeks (106) compensated cirrhosis, with HCV/HIV-1 co- infection
TN and TE with or without cirrhosis, with ESRD            Epclusa 12 weeks (59) GS-US-342-4062 requiring dialysis
TN = treatment-naïve patients; TE = treatment-experienced patients (including those who have failed a peginterferon alfa + ribavirin based regimen with or without an HCV protease inhibitor)

The ribavirin dose was weight-based (1,000 mg daily administered in two divided doses for patients < 75 kg and 1,200 mg for those ≥ 75 kg) and administered in two divided doses when used in combination with sofosbuvir in the ASTRAL-2 and ASTRAL-3 studies or in combination with Epclusa in the ASTRAL-4 study. Ribavirin dose adjustments were performed according to the ribavirin Prescribing Information. Serum HCV RNA values were measured during the clinical studies using the COBAS AmpliPrep/COBAS Taqman HCV test (version 2.0) with a lower limit of quantification (LLOQ) of 15 IU/mL. Sustained virologic response (SVR12), defined as HCV RNA less than LLOQ at 12 weeks after the cessation of treatment, was the primary endpoint to determine the HCV cure rate.

Clinical studies in patients without cirrhosis and patients with compensated cirrhosis Genotype 1, 2, 4, 5 and 6 HCV-infected adults – ASTRAL-1 (study 1138) ASTRAL-1 was a randomised, double-blind, placebo-controlled study that evaluated 12 weeks of treatment with Epclusa compared with 12 weeks of placebo in patients with genotype 1, 2, 4, 5, or 6 HCV infection. Patients with genotype 1, 2, 4 or 6 HCV infection were randomised in a 5:1 ratio to treatment with Epclusa for 12 weeks or placebo for 12 weeks. Patients with genotype 5 HCV infection were enrolled to the Epclusa group. Randomisation was stratified by HCV genotype (1, 2, 4, 6, and indeterminate) and the presence or absence of cirrhosis.

Demographics and baseline characteristics were balanced between the Epclusa and placebo group. Of the 740 treated patients, the median age was 56 years (range: 18 to 82); 60% of the patients were male; 79% were White, 9% were Black; 21% had a baseline body mass index of at least 30 kg/m2; the proportions of patients with genotype 1, 2, 4, 5, or 6 HCV infection were 53%, 17%, 19%, 5% and 7%, respectively; 69% had non-CC IL28B alleles (CT or TT); 74% had baseline HCV RNA levels of at least 800,000 IU/mL; 19% had compensated cirrhosis; and 32% were treatment-experienced.

Table 11 presents the SVR12 for the ASTRAL-1 study by HCV genotypes. No patients in the placebo group achieved SVR12.


Table 11: SVR12 in study ASTRAL-1 by HCV genotype
Epclusa 12 weeks
(n = 624)
Total                         GT-1                     GT-2           GT-4          GT-5         GT-6 (all GTs) GT-1a             GT-1b         Total        (n = 104)      (n = 116)     (n = 35)     (n = 41) (n = 624) (n = 210)         (n = 118)     (n = 328)
99%          98%            99%           98%          100%           100%          97%          100% SVR12
(618/624) (206/210)         (117/118)     (323/328) (104/104)         (116/116)     (34/35)      (41/41) Outcome for patients without SVR12
On- treatment
0/624        0/210          0/118         0/328         0/104         0/116         0/35         0/41 virologic failure
< 1%         < 1%           1%            1%
Relapsea                                                            0/104         0/116         0/35         0/41 (2/623)      (1/209)        (1/118)       (2/327)
1%           1%                           1%                                        3% Otherb                                  0/118                       0/104         0/116                      0/41 (4/624)      (3/210)                      (3/328)                                   (1/35) GT = genotype a The denominator for relapse is the number of patients with HCV RNA < LLOQ at their last on-treatment assessment.
b Other includes patients who did not achieve SVR12 and did not meet virologic failure criteria.

Genotype 2 HCV-infected adults – ASTRAL-2 (study 1139)
ASTRAL-2 was a randomised, open-label study that evaluated 12 weeks of treatment with Epclusa compared with 12 weeks of treatment with SOF+RBV in patients with genotype 2 HCV infection.
Patients were randomised in a 1:1 ratio to treatment with Epclusa for 12 weeks or SOF+RBV for 12 weeks. Randomisation was stratified by the presence or absence of cirrhosis and prior treatment experience (treatment-naïve versus treatment-experienced).

Demographics and baseline characteristics were balanced across the two treatment groups. Of the 266 treated patients, the median age was 58 years (range: 23 to 81); 59% of the patients were male; 88% were White, 7% were Black; 33% had a baseline body mass index of at least 30 kg/m2; 62% had non-CC IL28B alleles (CT or TT); 80% had baseline HCV RNA levels of at least 800,000 IU/mL; 14% had compensated cirrhosis and 15% were treatment-experienced.

Table 12 presents the SVR12 for the ASTRAL-2 study.

Table 12: SVR12 in study ASTRAL-2 (HCV genotype 2)
Epclusa                                 SOF+RBV
12 weeks                                12 weeks
(n = 134)                               (n = 132)
SVR12                                 99% (133/134)                           94% (124/132) Outcome for patients without SVR12
On-treatment virologic failure     0/134                                      0/132 Relapsea                           0/133                                      5% (6/132) Otherb                             1% (1/134)                                 2% (2/132) a    The denominator for relapse is the number of patients with HCV RNA < LLOQ at their last on-treatment assessment.
b    Other includes patients who did not achieve SVR12 and did not meet virologic failure criteria.

Treatment with Epclusa for 12 weeks demonstrated the statistical superiority (p = 0.018) over treatment with SOF+RBV for 12 weeks (treatment difference +5.2%; 95% confidence interval: +0.2% to +10.3%).

Genotype 3 HCV-infected adults – ASTRAL-3 (study 1140)
ASTRAL-3 was a randomised, open-label study that evaluated 12 weeks of treatment with Epclusa compared with 24 weeks of treatment with SOF+RBV in patients with genotype 3 HCV infection.
Patients were randomised in a 1:1 ratio to treatment with Epclusa for 12 weeks or SOF+RBV for 24 weeks. Randomisation was stratified by the presence or absence of cirrhosis and prior treatment experience (treatment-naïve versus treatment-experienced).


Demographics and baseline characteristics were balanced across the two treatment groups. Of the 552 treated patients, the median age was 52 years (range: 19 to 76); 62% of the patients were male; 89% were White, 9% were Asian; 1% were Black; 20% had a baseline body mass index of at least 30 kg/m2; 61% had non-CC IL28B alleles (CT or TT); 70% had baseline HCV RNA levels of at least 800,000 IU/mL, 30% had compensated cirrhosis and 26% were treatment-experienced.

Table 13 presents the SVR12 for the ASTRAL-3 study.

Table 13: SVR12 in study ASTRAL-3 (HCV genotype 3)
Epclusa                                 SOF+RBV
12 weeks                                24 weeks
(n = 277)                               (n = 275)
SVR12                                   95% (264/277)                           80% (221/275) Outcome for patients without SVR12
On-treatment virologic failure     0/277                                        < 1% (1/275) Relapsea                           4% (11/276)                                  14% (38/272) Otherb                             1% (2/277)                                   5% (15/275) a     The denominator for relapse is the number of patients with HCV RNA < LLOQ at their last on-treatment assessment.
b     Other includes patients who did not achieve SVR12 and did not meet virologic failure criteria.

Treatment with Epclusa for 12 weeks demonstrated the statistical superiority (p < 0.001) compared to treatment with SOF+RBV for 24 weeks (treatment difference +14.8%; 95% confidence interval: +9.6% to +20.0%).

SVR12 for selected subgroups are presented in Table 14.

Table 14: SVR12 for selected subgroups in study ASTRAL-3 (HCV genotype 3) Epclusa                                          SOF+RBV
12 weeks                                         24 weeksa
SVR12                  Treatment-naïve          Treatment-              Treatment-naïve         Treatment- (n = 206)                experienced             (n = 201)               experienced (n = 71)                                        (n = 69)
Without cirrhosis      98% (160/163)            91% (31/34)             90% (141/156)           71% (22/31) With cirrhosis         93% (40/43)              89% (33/37)             73% (33/45)             58% (22/38) a     Five patients with missing cirrhosis status in the SOF+RBV 24 week group were excluded from this subgroup analysis.

Clinical studies in patients with decompensated cirrhosis – ASTRAL-4 (study 1137) ASTRAL-4 was a randomised, open-label study in patients with genotype 1, 2, 3, 4, 5 or 6 HCV infection and CPT Class B cirrhosis. Patients were randomised in a 1:1:1 ratio to treatment with Epclusa for 12 weeks, Epclusa + RBV for 12 weeks or Epclusa for 24 weeks. Randomisation was stratified by HCV genotype (1, 2, 3, 4, 5, 6 and indeterminate).

Demographics and baseline characteristics were balanced across the treatment groups. Of the 267 treated patients, the median age was 59 years (range: 40 to 73); 70% of the patients were male; 90% were White, 6% were Black; 42% had a baseline body mass index of at least 30 kg/m2. The proportions of patients with genotype 1, 2, 3, 4 or 6 HCV were 78%, 4%, 15%, 3%, and < 1% (1 patient), respectively. No patients with genotype 5 HCV infection were enrolled. 76% of the patients had non-CC IL28B alleles (CT or TT); 56% had baseline HCV RNA levels of at least 800,000 IU/mL, 55% were treatment-experienced; 90% and 95% of patients had CPT Class B cirrhosis and Model for End Stage Liver Disease (MELD) score ≤ 15 at baseline, respectively.

Table 15 presents the SVR12 for the ASTRAL-4 study by HCV genotype.


Table 15: SVR12 in study ASTRAL-4 by HCV genotype
Epclusa                             Epclusa + RBV                 Epclusa 12 weeks                            12 weeks                      24 weeks (n = 90)                            (n = 87)                      (n = 90) Overall SVR12               83% (75/90)                         94% (82/87)                   86% (77/90) Genotype 1                  88% (60/68)                         96% (65/68)                   92% (65/71) Genotype 1a               88% (44/50)                         94% (51/54)                   93% (51/55) Genotype 1b               89% (16/18)                         100% (14/14)                  88% (14/16) Genotype 3                  50% (7/14)                          85% (11/13)                   50% (6/12) Genotype 2, 4 and 6         100% (8/8)a                         100% (6/6)b                   86% (6/7)c a     n = 4 for genotype 2 and n = 4 for genotype 4.
b     n = 4 for genotype 2 and n = 2 for genotype 4.
c     n = 4 for genotype 2, n = 2 for genotype 4 and n = 1 for genotype 6.

Table 16 presents the virologic outcome for patients with genotype 1 or 3 HCV infection in the ASTRAL-4 study.

No patients with genotype 2, 4 or 6 HCV infection experienced virologic failure.

Table 16: Virologic outcome for patients with genotype 1 and 3 HCV infection in study ASTRAL-4
Epclusa 12 weeks                    Epclusa + RBV 12 weeks          Epclusa 24 weeks Virologic failure (relapse and on-treatment failure)
Genotype 1a              7% (5/68)                           1% (1/68)                       4% (3/71) Genotype 1a           6% (3/50)                           2% (1/54)                       4% (2/55) Genotype 1b           11% (2/18)                          0% (0/14)                       6% (1/16) Genotype 3               43% (6/14)                          15% (2b/13)                     42% (5c/12) Otherd                   5% (4/82)                           2% (2/81)                       5% (4/83) a     No patients with genotype 1 HCV had on-treatment virologic failure.
b     One patient had on-treatment virologic failure; pharmacokinetic data from this patient was consistent with non-adherence to treatment.
c     One patient had on-treatment virologic failure.
d     Other includes patients who did not achieve SVR12 and did not meet virologic failure criteria.

Changes in the parameters found in the CPT score system in patients achieving SVR12 in ASTRAL-4 (all 3 regimens) are shown in Table 17.

Table 17: Changes in CPT score parameters from baseline to week 12 and 24 post-treatment in patients achieving SVR12, ASTRAL-4
Albumin        Bilirubin                   INR               Ascites        Encephalopathy Post-treatment Week 12 (N = 236), % (n/N)
Decreased score              34.5%           17.9%                                        7.9% 2.2% (5/229)                      5.2% (12/229)
(Improvement)               (79/229)        (41/229)                                    (18/229) No change                    60.3%           76.4%                         96.5%          89.1% 91.3% (209/229)
(138/229)       (175/229)                     (221/229)     (204/229) Increased score               5.2%            5.7%                                         3.1% 1.3% (3/229)                       3.5% (8/229)
(Worsening)                 (12/229)        (13/229)                                     (7/229) No assessment                   7               7                           7                7                7 Post-treatment Week 24 (N = 236), % (n/N)
Decreased score              39.4%           16.4%                                        15.0% 2.3% (5/213)                      9.4% (20/213)
(Improvement)               (84/213)        (35/213)                                    (32/213) No change                    54.0%           80.8%                         94.8%          81.2% 88.3% (188/213)
(115/213)       (172/213)                     (202/213)     (173/213) Increased score               6.6%                                                         3.8% 2.8% (6/213)                2.8% (6/213)                       2.3% (5/213) (Worsening)                 (14/213)                                                     (8/213) No assessment                  23              23                           23              23                23 Note: Baseline frequency of ascites was: 20% none, 77% mild/moderate, 3% severe Baseline frequency of encephalopathy was: 38% none, 62% grade 1-2.


Clinical studies in patients with HCV/HIV-1 Co-infection – ASTRAL-5 (study 1202) ASTRAL-5 evaluated 12 weeks of treatment with Epclusa in patients with genotype 1, 2, 3, or 4 HCV infection who were co-infected with HIV-1 (HCV genotype 5 and 6 allowed, but no such patients were included). Patients were on a stable HIV-1 antiretroviral therapy that included emtricitabine/tenofovir disoproxil fumarate or abacavir/lamivudine administered with a ritonavir boosted protease inhibitor (atazanavir, darunavir, or lopinavir), rilpivirine, raltegravir or emtricitabine/tenofovir disoproxil fumarate /elvitegravir/cobicistat.

Of the 106 treated patients, the median age was 57 years (range: 25 to 72); 86% of the patients were male; 51% were White; 45% were Black; 22% had a baseline body mass index ≥ 30 kg/m2; 19 patients (18%) had compensated cirrhosis; and 29% were treatment experienced. The overall mean CD4+ count was 598 cells/µL (range: 183−1513 cells/µL).

Table 18 presents the SVR12 for the ASTRAL-5 study by HCV genotype.

Table 18: SVR12 in study ASTRAL-5 by HCV genotype
Epclusa 12 weeks
(n = 106)
Total                                   GT-1                         GT-2           GT-3           GT-4 (all GTs)         GT-1a              GT-1b          Total            (n = 11)       (n = 12)       (n = 5) (n = 106)         (n = 66)           (n = 12)       (n = 78)
95%               95%                92%            95%              100%           92%            100% SVR12
(101/106)         (63/66)            (11/12)        (74/78)          (11/11)        (11/12)        (5/5) Outcome for patients without SVR
On- treatment
0/106             0/66               0/12             0/78           0/11           0/12           0/5 virologic failure
2%                3%                                  3%
Relapsea                                         0/11                            0/11           0/11           0/5 (2/103)           (2/65)                              (2/76) b     3%                2%                 8%               3%                            8% Other                                                                            0/11                          0/5 (3/106)           (1/66)             (1/12)           (2/78)                        (1/12) GT = genotype a The denominator for relapse is the number of patients with HCV RNA < LLOQ at their last on-treatment assessment.
b Other includes patients who did not achieve SVR12 and did not meet virologic failure criteria.

SVR12 was achieved by 19/19 patients with cirrhosis. No patient had HIV-1 rebound during the study, and CD4+ counts were stable during treatment.

Clinical studies in patients with Renal Impairment – study 4062
Study 4062 was an open-label clinical study that evaluated 12 weeks of treatment with Epclusa in 59 HCV-infected patients with ESRD requiring dialysis. The proportions of patients with genotype 1, 2, 3, 4, 6 or indeterminate HCV infection were 42%, 12%, 27%, 7% , 3%, and 9%, respectively. At baseline, 29% of patients had cirrhosis, 22% were treatment experienced, 32% had received a kidney transplant, 92% were on haemodialysis, and 8% were on peritoneal dialysis; mean duration on dialysis was 7.3 years (range: 0 to 40 years). The overall SVR rate was 95% (56/59); of the three patients that did not achieve SVR12, one had completed Epclusa treatment and relapsed and two did not meet virologic failure criteria.

Paediatric population
The efficacy of 12 weeks of treatment with sofosbuvir/velpatasvir in HCV-infected paediatric patients aged 12 years and older with genotype 1,2,3,4 or 6 HCV infection was evaluated in a Phase 2, open- label clinical study in 102 patients with HCV infection.
A total of 80 patients (78%) were treatment-naïve and 22 patients (22%) were treatment-experienced.
The median age was 15 years (range: 12 to 17); 51% of the patients were female; 73% were White, 9% were Black, and 11% were Asian; 14% were Hispanic/Latino; mean body mass index was 22.7 kg/m2 (range: 12.9 to 48.9 kg/m2); mean weight was 61 kg (range 22 to 147 kg); 58% had baseline HCV RNA levels greater than or equal to 800,000 IU/mL; the proportions of subjects with genotype 1, 
2, 3, 4, or 6 HCV infection were 74%, 6%, 12%, 2%, and 6%, respectively; no patients had known cirrhosis. The majority of patients (89%) had been infected through vertical transmission.

The SVR rate was 95% overall (97/102), 93% (71/76) in patients with genotype 1 HCV infection, and 100% in patients with genotype 2 (6/6), genotype 3 (12/12), genotype 4 (2/2), and genotype 6 (6/6) HCV infection. One patient who discontinued treatment early relapsed; the other four patients who did not achieve SVR12 did not meet virologic failure criteria (e.g., lost to follow-up).

Elderly
Clinical studies of Epclusa included 156 patients aged 65 and over (12% of total number of patients in the Phase 3 clinical studies). The response rates observed for patients ≥ 65 years of age were similar to that of patients < 65 years of age, across treatment groups.

Pharmacokinetic Properties

5.2   Pharmacokinetic properties
Absorption

The pharmacokinetic properties of sofosbuvir, GS-331007 and velpatasvir have been evaluated in healthy adult subjects and in patients with chronic hepatitis C. Following oral administration of Epclusa, sofosbuvir was absorbed quickly and the peak median plasma concentration was observed 1 hour post-dose. Median peak plasma concentration of GS-331007 was observed 3 hours post-dose.
Velpatasvir median peak concentrations were observed at 3 hours post-dose.

Based on the population pharmacokinetic analysis in HCV-infected patients, mean steady-state AUC0-24 for sofosbuvir (n = 982), GS-331007 (n = 1,428) and velpatasvir (n = 1,425) were 1,260, 13,970 and 2,970 ng•h/mL, respectively. Steady-state Cmax for sofosbuvir, GS-331007 and velpatasvir were 566, 868 and 259 ng/mL, respectively. Sofosbuvir and GS-331007 AUC0-24 and Cmax were similar in healthy adult subjects and patients with HCV infection. Relative to healthy subjects (n = 331), velpatasvir AUC0-24 and Cmax were 37% lower and 41% lower, respectively in HCV-infected patients.

Effects of food
Relative to fasting conditions, the administration of a single dose of Epclusa with a moderate fat (~600 kcal, 30% fat) or high fat (~800 kcal, 50% fat) meal resulted in a 34% and 21% increase in velpatasvir AUC0-inf, respectively, and a 31% and 5% increase in velpatasvir Cmax, respectively. The moderate or high fat meal increased sofosbuvir AUC0-inf by 60% and 78%, respectively, but did not substantially affect the sofosbuvir Cmax. The moderate or high fat meal did not alter GS-331007 AUC0-inf, but resulted in a 25% and 37% decrease in its Cmax, respectively. The response rates in Phase 3 studies were similar in HCV-infected patients who received Epclusa with food or without food. Epclusa can be administered without regard to food.

Distribution

Sofosbuvir is approximately 61-65% bound to human plasma proteins and the binding is independent of drug concentration over the range of 1 µg/mL to 20 µg/mL. Protein binding of GS-331007 was minimal in human plasma. After a single 400 mg dose of [14C]-sofosbuvir in healthy subjects, the blood to plasma ratio of [14C]-radioactivity was approximately 0.7.

Velpatasvir is > 99.5% bound to human plasma proteins and binding is independent of drug concentration over the range of 0.09 µg/mL to 1.8 µg/mL. After a single 100 mg dose of [14C]-velpatasvir in healthy subjects, the blood to plasma ratio of [14C]-radioactivity ranged between 0.52 and 0.67.


Biotransformation

Sofosbuvir is extensively metabolised in the liver to form the pharmacologically active nucleoside analog triphosphate GS-461203. The metabolic activation pathway involves sequential hydrolysis of the carboxyl ester moiety catalysed by human cathepsin A (CatA) or carboxylesterase 1 (CES1) and phosphoramidate cleavage by histidine triad nucleotide-binding protein 1 (HINT1) followed by phosphorylation by the pyrimidine nucleotide biosynthesis pathway. Dephosphorylation results in the formation of nucleoside metabolite GS-331007 that cannot be efficiently rephosphorylated and lacks anti-HCV activity in vitro. Sofosbuvir and GS-331007 are not substrates or inhibitors of UGT1A1 or CYP3A4, CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, and CYP2D6 enzymes. After a single 400 mg oral dose of [14C]-sofosbuvir, GS-331007 accounted for approximately > 90% of total systemic exposure.

Velpatasvir is a substrate of CYP2B6, CYP2C8, and CYP3A4 with slow turnover. Following a single dose of 100 mg [14C]-velpatasvir, the majority (> 98%) of radioactivity in plasma was parent drug.
The monohydroxylated and desmethylated velpatasvir were the metabolites identified in human plasma. Unchanged velpatasvir is the major species present in faeces.

Elimination

Following a single 400 mg oral dose of [14C]-sofosbuvir, mean total recovery of the [14C]-radioactivity was greater than 92%, consisting of approximately 80%, 14%, and 2.5% recovered in urine, faeces, and expired air, respectively. The majority of the sofosbuvir dose recovered in urine was GS-331007 (78%) while 3.5% was recovered as sofosbuvir. These data indicate that renal clearance is the major elimination pathway for GS-331007. The median terminal half-lives of sofosbuvir and GS-331007 following administration of Epclusa were 0.5 and 25 hours, respectively.

Following a single 100 mg oral dose of [14C]-velpatasvir, mean total recovery of the [14C]-radioactivity was 95%, consisting of approximately 94% and 0.4% recovered from the faeces and urine, respectively. Unchanged velpatasvir was the major species in faeces accounting for a mean of 77% of the administered dose, followed by monohydroxylated velpatasvir (5.9%) and desmethylated velpatasvir (3.0%). These data indicate that biliary excretion of parent drug was a major route of elimination for velpatasvir. The median terminal half-life of velpatasvir following administration of Epclusa was approximately 15 hours.

Linearity/non-linearity

Velpatasvir AUC increases in a nearly dose proportional manner over the dose range of 25 mg to 150 mg. Sofosbuvir and GS-331007 AUCs are near dose-proportional over the dose range of 200 mg to 1,200 mg.

In vitro potential for sofosbuvir/velpatasvir drug-drug interactions

Sofosbuvir and velpatasvir are substrates of drug transporters P-gp and BCRP while GS-331007 is not.
Velpatasvir is also a substrate of OATP1B. In vitro, slow metabolic turnover of velpatasvir by CYP2B6, CYP2C8, and CYP3A4 was observed.

Velpatasvir is an inhibitor of drug transporter P-gp, BCRP, OATP1B1 and OATP1B3 and its involvement in drug interactions with these transporters is primarily limited to the process of absorption. At clinically relevant plasma concentration, velpatasvir is not an inhibitor of hepatic transporters bile salt export pump (BSEP), sodium taurocholate cotransporter protein (NTCP), OATP2B1, OATP1A2 or organic cation transporter (OCT) 1, renal transporters OCT2, OAT1, OAT3, multidrug resistance-associated protein 2 (MRP2) or multidrug and toxin extrusion protein (MATE) 1, or CYP or uridine glucuronosyltransferase (UGT) 1A1 enzymes.

Sofosbuvir and GS-331007 are not inhibitors of drug transporters P-gp, BCRP, MRP2, BSEP, OATP1B1, OATP1B3 and OCT1. GS-331007 is not an inhibitor of OAT1, OCT2, and MATE1.
Pharmacokinetics in special populations

Race and gender
No clinically relevant pharmacokinetic differences due to race or gender have been identified for sofosbuvir, GS-331007 or velpatasvir.

Elderly
Population pharmacokinetic analysis in HCV-infected patients showed that within the age range (18 to 82 years) analysed, age did not have a clinically relevant effect on the exposure to sofosbuvir, GS-331007, or velpatasvir.

Renal impairment
A summary of the effect of varying degrees of renal impairment (RI) on the exposures of the components of Epclusa compared to subjects with normal renal function, as described in the text below, are provided in Table 18.

Table 18: Effect of Varying Degrees of Renal Impairment on Exposures (AUC) of Sofosbuvir, GS-331007, and Velpatasvir Compared to Subjects with Normal Renal Function HCV-Negative Subjects                               HCV-Infected
Subjects
Mild RI    Moderate RI     Severe RI        ESRD Requiring        Severe RI     ESRD (eGFR ≥50    (eGFR ≥30      (eGFR <30             Dialysis           (eGFR      Requiring and <80      and <50      mL/min/1.7      Dosed 1     Dosed 1        <30       Dialysis mL/min/1.7   mL/min/1.73       3m2)        hr Before    hr After    mL/min/1.
3m2)          m 2)                       Dialysis    Dialysis     73m2) Sofosbuvir     1.6-fold↑     2.1-fold↑      2.7-fold↑    1.3-fold↑    1.6-fold↑   ~2-fold↑    1.8-fold↑ GS-331007      1.6-fold↑     1.9-fold↑      5.5-fold↑    ≥10-fold↑ ≥20-fold↑      ~7-fold↑    18-fold↑ Velpatasvir        -             -          1.5-fold↑        -            -           -       1.4-fold↑ 
The pharmacokinetics of sofosbuvir was studied in HCV negative adult patients with mild (eGFR ≥ 50 and < 80 mL/min/1.73 m2), moderate (eGFR ≥ 30 and < 50 mL/min/1.73 m2), severe renal impairment (eGFR < 30 mL/min/1.73 m2) and patients with ESRD requiring haemodialysis following a single 400 mg dose of sofosbuvir relative to patients with normal renal function (eGFR
> 80 mL/min/1.73 m2). GS-331007 is efficiently removed by haemodialysis with an extraction coefficient of approximately 53%. Following a single 400 mg dose of sofosbuvir, a 4 hour haemodialysis removed 18% of administered dose .

In HCV-infected patients with severe renal impairment treated with sofosbuvir 200 mg with ribavirin (n=10) or sofosbuvir 400 mg with ribavirin (n=10) for 24 weeks or ledipasvir/sofosbuvir 90/400 mg (n=18) for 12 weeks, the pharmacokinetics of sofosbuvir and GS-331007 were consistent with that observed in HCV negative adult patients with severe renal impairment.

The pharmacokinetics of velpatasvir was studied with a single dose of 100 mg velpatasvir in HCV negative patients with severe renal impairment (eGFR < 30 mL/min by Cockcroft-Gault).

The pharmacokinetics of sofosbuvir, GS-331007, and velpatasvir were studied in HCV-infected patients with ESRD requiring dialysis treated with Epclusa (n=59) for 12 weeks, and compared to patients without renal impairment in the sofosbuvir/velpatasvir Phase 2/3 studies.

Hepatic impairment
The pharmacokinetics of sofosbuvir was studied following 7-day dosing of 400 mg sofosbuvir in HCV-infected adult patients with moderate and severe hepatic impairment (CPT Class B and C).
Relative to patients with normal hepatic function, the sofosbuvir AUC0-24 was 126% and 143% higher in moderate and severe hepatic impairment, while the GS-331007 AUC0-24 was 18% and 9% higher, respectively. Population pharmacokinetics analysis in HCV-infected adult patients indicated that cirrhosis (including decompensated cirrhosis) had no clinically relevant effect on the exposure to sofosbuvir and GS-331007.

The pharmacokinetics of velpatasvir was studied with a single dose of 100 mg velpatasvir in HCV negative adult patients with moderate and severe hepatic impairment (CPT Class B and C). Compared to subjects with normal hepatic function velpatasvir total plasma exposure (AUCinf) was similar in patients with moderate or severe hepatic impairment. Population pharmacokinetics analysis in HCV-infected patients indicated that cirrhosis (including decompensated cirrhosis) had no clinically relevant effect on the exposure to velpatasvir (see section 4.2).

Body weight
In adults, body weight did not have a clinically significant effect on sofosbuvir or velpatasvir exposure according to a population pharmacokinetic analysis.

Paediatric population
Sofosbuvir, GS-331007 and velpatasvir exposures in paediatric patients aged 12 years and older receiving oral once daily doses of sofosbuvir/velpatasvir 400 mg/100 mg were similar to those in adults receiving once daily doses of sofosbuvir/velpatasvir 400 mg/100 mg. The pharmacokinetics of sofosbuvir, GS-331007 and velpatasvir in paediatric patients aged less than 12 years and weighing <30 kg have not been established (see section 4.2).