Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1    Pharmacodynamic properties

Pharmacotherapeutic group: Antivirals for systemic use; Direct-acting antivirals, ATC code: J05AP56 
Mechanism of action

Sofosbuvir is a pan-genotypic inhibitor of the HCV NS5B RNA-dependent RNA polymerase, which is required 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. In a biochemical assay, GS-461203 inhibited the polymerase activity of the recombinant NS5B from HCV genotype 1b, 2a, 3a, and 4a. GS-461203 is neither an inhibitor of human DNA and RNA polymerases nor an inhibitor of mitochondrial RNA polymerase.

Velpatasvir is a pan-genotypic HCV inhibitor targeting the HCV NS5A protein, which is required for viral replication.

Voxilaprevir is a pan-genotypic inhibitor of the HCV NS3/4A protease. Voxilaprevir acts as a noncovalent, reversible inhibitor of the NS3/4A protease.

Antiviral activity

The 50% effective concentration (EC50) values of sofosbuvir, velpatasvir and voxilaprevir against full-length or chimeric replicons encoding NS5B, NS5A and NS3 protease sequences from the laboratory strains are presented in Table 4. The EC50 values of sofosbuvir, velpatasvir and voxilaprevir against clinical isolates are presented in Table 5.

Table 4: Activity of sofosbuvir, velpatasvir and voxilaprevir against full-length or chimeric laboratory replicons

Replicon             Sofosbuvir EC50, nMa         Velpatasvir EC50, nMa          Voxilaprevir EC50, nMa genotype
1a                   40                           0.014                          3.9e 1b                   110                          0.016                          3.3e 2a                   50                           0.005-0.016c                   3.7-4.5e
2b                   15b                          0.002-0.006c                   1.8-6.6f
3a                   50                           0.004                          6.1f 4a                   40                           0.009                          2.9e
4d                   33                           0.004                          3.2e
5a                   15b                          0.021-0.054d                   1.9f 6a                   14-25b                       0.006-0.009                    3.0-4.0e 6e                   NA                           0.130d                         0.33f 6n                   NA                           NA                             2.9f 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.
e. Stable cell lines expressing Renilla luciferase-encoding replicons.
f. Data obtained from transiently transfected replicons.


Table 5: Activity of sofosbuvir, velpatasvir and voxilaprevir against transient replicons containing NS5A, NS5B or NS3 protease from clinical isolates

Replicon     Replicons containing        Replicons containing NS5A           Replicons containing NS3 genotype     NS5B from clinical          from clinical isolates              protease from clinical isolates                                                        isolates Number of Median            Number             Median           Number      Median clinical     sofosbuvir     of clinical        velpatasvir      of clinical voxilaprevir isolates     EC50, nM       isolates           EC50, nM         isolates    EC50, nM (range)                           (range)                      (range) 1a           67           62             23                 0.019            58          0.59 (29-128)                          (0.011-0.078)                (0.14-19.16) 1b           29           102            34                 0.012            29          0.50 (45-170)                          (0.005-0.500)                (0.19-2.87) 2a           1            28             8                  0.011            18          2.8
(0.006-0.364)                (1.78-6.72)
2b           14          30              16                 0.002            43          2.1
(14-81)                            (0.0003-0.007)               (0.92-8.3) 3a           106         81              38                 0.005            32          6.3 (24-181)                           (0.002-1.871)                (1.3-21.48) 4a           NA          NA              5                  0.002            58          0.52
(0.001-0.004)                (0.12-1.7)
4d           NA          NA              10                 0.007            11          0.85
(0.004-0.011)                (0.41-1.1)
4r           NA          NA              7                  0.003            1           1.15
(0.002-0.006)                NA
5a           NA          NA              42                 0.005            16          1.8 (0.001-0.019)                (0.87-5.63)
6a           NA          NA              26                 0.007            15          2.7 (0.0005-0.113)               (0.23-7.35)
6e           NA          NA              15                 0.024            12          0.2 (0.005-0.433)                (0.12-0.43)
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 and voxilaprevir by 13- and 6.8-fold, respectively, against genotype 1a HCV replicons.

Resistance

In cell culture
For sofosbuvir, the NS5B substitution S282T was selected in genotype 1-6 replicons and was associated with 2- to 18-fold reduced susceptibility to sofosbuvir.

For velpatasvir in genotype 1-6 replicons, resistance-associated substitutions selected in 2 or more genotypes were L31I/V and Y93H. Site directed mutagenesis of NS5A resistance associated variants (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 RAV tested in genotypes 2a, 4a or 5a conferred a > 100-fold reduction in velpatasvir susceptibility.

For voxilaprevir in genotype 1-6 replicons, resistance-associated substitutions selected in 2 or more genotypes were Q41H, A156V/T/L and D168E/H/Y. Site directed mutagenesis of known NS3 RAVs showed that substitutions conferring a > 100-fold reduction in voxilaprevir susceptibility are A156V, A156T or A156L in genotype 1a, 1b, 2a, 3a and 4. No individual RAV tested in genotypes 2b, 5a or 6a conferred a > 100-fold reduction in voxilaprevir susceptibility.

For both velpatasvir and voxilaprevir, combinations of RAVs often showed greater reductions in susceptibility than individual RAVs alone.
Cross resistance in cell culture
Voxilaprevir is active in vitro against most of the NS3 RAVs that confer resistance to first generation NS3/4A protease inhibitors. Additionally, velpatasvir is active in vitro against most of the NS5A RAVs that confer resistance to ledipasvir and daclatasvir. Sofosbuvir, velpatasvir, and voxilaprevir were fully active against substitutions associated with resistance to other classes of DAAs with different mechanisms of actions, e.g. voxilaprevir was fully active against NS5A and NS5B NI RAVs.

In clinical studies
Studies in DAA-experienced patients
Of the 263 NS5A inhibitor-experienced patients treated with sofosbuvir/velpatasvir/voxilaprevir for 12 weeks in POLARIS-1 (see Table 10), 7 of 263 (3%) patients (2 with genotype 1, 4 with genotype 3, and 1 with genotype 4) did not achieve sustained virologic response (SVR12) and qualified for resistance analysis; 6 relapsed and 1 experienced virologic breakthrough with pharmacokinetic data consistent with nonadherence. The patient with genotype 1a and virologic breakthrough developed the NS5A RAVs L31M and Y93H. One patient with genotype 4d who relapsed developed the NS5A RAV Y93H. No NS3, NS5A, or NS5B nucleoside inhibitor (NI) RAVs emerged in the other 5 patients who relapsed.

Of the 182 DAA-experienced patients treated with sofosbuvir/velpatasvir/voxilaprevir for 12 weeks in POLARIS-4 (see Table 11), 1 of 182 (1%) patients relapsed and qualified for resistance analysis.
No NS3, NS5A, or NS5B NI RAVs emerged in this patient infected with genotype 1a HCV.

Studies in DAA-naïve patients
In the POLARIS-2 sofosbuvir/velpatasvir/voxilaprevir 8-week treatment group (see Table 12), a total of 21 of 501 (4%) patients (16 with genotype 1, 2 with genotype 2, 2 with genotype 4, and 1 with genotype 5) qualified for resistance analysis due to relapse. Of these 21 patients, 1 patient had virus with emergent NS5A RAVs Q30R and L31M at failure. No NS3 and NS5B NI RAVs emerged in any of these 21 patients at failure. In the sofosbuvir/velpatasvir 12-week treatment group, a total of 3 of 440 (1%) patients (2 with genotype 1, 1 with genotype 4) qualified for resistance analysis due to relapse. Of these 3 patients, 1 patient (33%) had virus with emergent NS5A RAV Y93N at failure.
No NS3 and NS5B NI RAVs emerged in any of these 3 patients.

In the POLARIS-3 sofosbuvir/velpatasvir/voxilaprevir 8-week treatment group (see Table 14), 2 of 110 (2%) patients (genotype 3) qualified for resistance analysis due to relapse. No NS3, NS5A,
or NS5B NI RAVs emerged in either of these patients. In the sofosbuvir/velpatasvir 12-week treatment group, 2 of 109 (2%) patients qualified for resistance analysis due to virologic failure. Both of these patients had virus with emergent NS5A RAV Y93H at failure. No NS3 or NS5B NI RAVs emerged in either of these patients.

Effect of baseline HCV resistance-associated variants on treatment outcome 
Studies in DAA-experienced patients
Analyses were conducted to explore the association between pre-existing baseline NS3 and NS5A RAVs and treatment outcome for patients that had previously been treated with DAA regimens and received sofosbuvir/velpatasvir/voxilaprevir for 12 weeks in POLARIS-1 and POLARIS-4. These are shown in Table 6.


Table 6: SVR12 in DAA-experienced patients with or without baseline NS3 or NS5A RAVs by study  sofosbuvir/velpatasvir/voxilaprevir 12 weeks
POLARIS-1 (n = 260)              POLARIS-4 (n = 179)
No NS3 or NS5A RAVs                      98% (42/43)                      99% (85/86) Any NS3 or NS5A RAV                      97% (199/205)                    100% (83/83) NS3 Only                                 100% (9/9)                       100% (39/39) NS5A Only                                97% (120/124)                    100% (40/40) NS3 and NS5A                             97% (70/72)                      100% (4/4) RAVs not determined for both             100% (12/12)                     100% (10/10) NS3 and NS5Aa a. Patients with NS3 and/or NS5A gene sequencing failure.

SVR12 was achieved in 18 of 19 (95%) patients who had baseline NS5B NI RAVs in POLARIS-1, including 2 patients who had virus with the S282T NS5B NI RAV in addition to NS5A RAVs at baseline. In POLARIS-4, a total of 14 patients had virus with NS5B NI RAVs at baseline and all achieved SVR12.

Studies in DAA-naïve patients
Analyses were conducted to explore the association between pre-existing baseline NS3 and NS5A RAVs and treatment outcome for patients that had not previously been treated with DAA regimens and received sofosbuvir/velpatasvir/voxilaprevir for 8 weeks in POLARIS-2 and POLARIS-3. These are shown in Table 7.

Table 7: SVR12 in DAA-naïve patients with or without baseline NS3 or NS5A RAVs by study  sofosbuvir/velpatasvir/voxilaprevir 8 weeks
POLARIS-2                 POLARIS-3
(n = 498)                 (n = 108)
No NS3 or NS5A RAVs                    98% (224/229)             98% (80/82) Any NS3 or NS5A RAV                    94% (234/250)             100% (23/23) NS3 only                              91% (100/110)            100% (2/2) NS5A only                             95% (114/120)            100% (20/20) NS3 and NS5A                          100% (20/20)             100% (1/1) RAVs not determined for both           100% (19/19)              100% (3/3) NS3 and NS5Aa a. Patients with NS3 and/or NS5A gene sequencing failure.

SVR12 was achieved in all 39 patients who had baseline NS5B NI RAVs in POLARIS-2 and 2 of 3 (67%) patients in POLARIS-3. The NS5B NI RAV S282T was not detected in any patient in POLARIS-2 and POLARIS-3 studies. Among patients with genotype 1a in POLARIS-2, SVR12 was 87% (53/61) for those with Q80K/L/R RAVs and 94% (99/105) for those without Q80K/L/R RAVs.

Clinical efficacy

The efficacy of Vosevi (sofosbuvir [SOF]/velpatasvir [VEL]/voxilaprevir [VOX]) was evaluated in four Phase 3 studies, two studies in DAA-experienced patients and two studies in DAA-naïve patients with, genotype 1 to 6 HCV infection without cirrhosis or with compensated cirrhosis, as summarised in Table 8. Demographics and baseline characteristics for all studies are detailed in Table 9.


Table 8: Studies conducted with Vosevi

Study             Population                  Study arms and duration             Additional study details (Number of patients treated)
Placebo-controlled study in which patients with GT1 infection were
NS5A inhibitor-             • SOF/VEL/VOX 12 weeks              randomised in a 1:1 ratio to POLARIS-1 experienced patients,         (N=263)                           SOF/VEL/VOX or placebo for (randomised
GT1-6, with or without      • Placebo 12 weeks                  12 weeks. Patients with GT2-6 double blind) cirrhosis                     (N=152)                           infection were enrolled into the SOF/VEL/VOX 12 week group only.
Patients with GT1-3 infection were
DAA-experienced                                                 randomised in a 1:1 ratio to • SOF/VEL/VOX 12 weeks patients (who have not                                          SOF/VEL/VOX or SOF/VEL for POLARIS-4                                       (N=182) received an NS5A                                                12 weeks. Patients with GT4-6 (open label) inhibitor), GT1-6, with     • SOF/VEL 12 weeks                  infection were enrolled into the (N=151) or without cirrhosis                                            SOF/VEL/VOX 12 week group only.
Patients with GT1-4 were randomised in a 1:1 ratio to
DAA-naïve patients,         • SOF/VEL/VOX 8 weeks
SOF/VEL/VOX for 8 weeks or
POLARIS-2         GT 1, 2, 4, 5, or 6, with     (N=501)
SOF/VEL for 12 weeks. Patients
(open label)      or without cirrhosis        • SOF/VEL 12 weeks with GT5-6 infection were enrolled
GT 3 without cirrhosis        (N=440) into the SOF/VEL/VOX 8 week group only.
• SOF/VEL/VOX 8 weeks
Patients were randomised in a 1:1
POLARIS-3         DAA-naïve patients            (N=110) ratio to SOF/VEL/VOX for
(open label)      with GT 3 and cirrhosis     • SOF/VEL 12 weeks
8 weeks or SOF/VEL for 12 weeks.
(N=109)
DAA: direct-acting antiviral; GT: genotype; SOF: sofosbuvir; VEL: velpatasvir; VOX: voxilaprevir 
Table 9: Demographics and baseline characteristics for patients enrolled into POLARIS-1, -2, -3 and -4 
Studies with DAA-experienced                Studies with DAA-naïve Patients Patients
Patient disposition                POLARIS-1           POLARIS-4               POLARIS-2           POLARIS-3 (n =415)            (n =333)                (n =941)            (n =219) Age (years) median (range)         59 (27-84)          58 (24-85)              55 (18-82)          56 (25-75) Male Gender                        77% (321)           77% (257)               52% (492)           72% (157) Race
Black/African American            14% (60)                 9% (29)             10% (95)           < 1% (1) White                             81% (335)                87% (291)           80% (756)          90% (197) Hispanic/Latino                   6% (25)                  8% (27)             9% (84)            8% (17) Genotype
Genotype 1a                       53% (218)              29% (98)             36% (341)            0 Genotype 1b                       18% (76)               14% (46)             13% (122)            0 Genotype 2                        1% (5)                 19% (64)             12% (116)            0 Genotype 3                        19% (78)               32% (106)            19% (181)            100% (219) Genotype 4                        5% (22)                5.7% (19)            13% (120)            0 Genotype 5                        < 1% (1)               0                    2% (18)              0 Genotype 6                        2% (8)                 0                    4% (39)              0 IL28B CC                           18% (74)               19% (62)             32% (302)           42% (93) HCV RNA ≥ 800,000 IU/mL            74% (306)              75% (249)            69% (648)           69% (151) Compensated cirrhosis              41% (172)              46% (153)            18% (174)           100% (219) Site
US                                 57% (236)                56% (188)           59% (552)          44% (96) Non-US                             43% (179)                44% (145)           41% (389)          56% (123) 
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 per 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 DAA-experienced patients
NS5A inhibitor-experienced adults (POLARIS-1)
Table 10 presents the SVR12 by HCV genotype for the POLARIS-1 study. The median time between prior DAA failure and first dose of Vosevi for patients enrolled into POLARIS-1 was 39 weeks (range: 11 to 299 weeks). No patients in the placebo group achieved SVR4.

Table 10: SVR12 in NS5A-inhibitor experienced patients by HCV genotype in study POLARIS-1* 
SOF/VEL/VOX 12 weeks (n = 263)

Total                        GT-1                    GT-2        GT-3        GT-4        GT-5      GT-6 (all         GT-1a          GT-1b       Total b      (n = 5)     (n = 78)    (n = 22)    (n = 1)   (n = 6) GTs)a        (n = 101)      (n = 45)    (n = 150)
(n = 263)
96%          96%            100%        97%          100%        95%         91%         100%      100% SVR12                                                                       (74/78) (253/263) (97/101)          (45/45)     (146/150)    (5/5)                   (20/22)     (1/1)     (6/6) Outcome for patients without SVR
On- treatment     <1%          1%                         1%
0/45                     0/5         0/78        0/22        0/1       0/6 virologic (1/263)       (1/101)                    (1/150) failurec
2%           1%                       1%                       5%          5%
Relapsed                               0/45                     0/5                                 0/1       0/6 (6/261)      (1/100)                  (1/149)                  (4/78)      (1/21) 1%           2%                       1%                                   5% Othere                                 0/45                     0/5         0/78                    0/1       0/6 (3/263)      (2/101)                  (2/150)                              (1/22) GT = genotype
* The most common prior NS5A inhibitors were ledipasvir (LDV) (51%), daclatasvir (27%), and ombitasvir (11%).
a. One patient with undetermined genotype achieved SVR12.
b. Four patients had genotype 1 subtypes other than genotype 1a or genotype 1b; all 4 patients achieved SVR12.
c. Pharmacokinetic data for the 1 patient with on-treatment virologic failure was consistent with non-adherence.
d. The denominator for relapse is the number of patients with HCV RNA < LLOQ at their last on-treatment assessment.
e. Other includes patients with missing data and those who discontinued treatment prior to virologic suppression.

DAA-experienced adults who had not received an NS5A inhibitor (POLARIS-4) Table 11 presents the SVR12 by HCV genotype and virologic outcome for the POLARIS-4 study.
The median time between prior DAA failure and first dose of Vosevi or sofosbuvir/velpatasvir for patients enrolled into POLARIS-4 was 76 weeks (range: 10 to 549 weeks).


Table 11: SVR12 by HCV genotype and virologic outcome in study POLARIS-4 
SOF/VEL/VOX 12 weeks                  SOF/VEL
(n = 182)                             12 weeks
(n = 151)
Overall SVR12          98% (178/182)                               90% (136/151) Genotype 1             97% (76/78)                                 91% (60/66) Genotype 1a           98% (53/54)                                  89% (39/44) Genotype 1b           96% (23/24)                                  95% (21/22) Genotype 2             100% (31/31)                                97% (32/33) Genotype 3             96% (52/54)                                 85% (44/52) Genotype 4             100% (19/19)                                0/0 Outcome for patients without SVR
On-treatment           0/182                                       1% (1/151) virologic failurea
Relapseb               1% (1/182)                                  9% (14/150) Otherc                 2% (3/182)                                  0/151 a. The majority (85%) of patients previously failed a regimen containing sofosbuvir.
b. The denominator for relapse is the number of patients with HCV RNA < LLOQ at their last on-treatment assessment.
c. Other includes patients with missing data and those who discontinued treatment prior to virologic suppression.

Clinical studies in DAA-naïve patients
DAA-naïve adults with genotype 1, 2, 3, 4, 5, or 6 HCV infection (POLARIS-2) Table 12 presents the SVR12 by HCV genotype and virologic outcome for the POLARIS-2 study.

Table 12: SVR12 by HCV genotype and virologic outcome in study POLARIS-2* 
SOF/VEL/VOX                                SOF/VEL
8 weeks                                    12 weeks
(n = 501)                                  (n = 440)
Overall SVR12a            95% (477/501)                              98% (432/440) Genotype 1b               93% (217/233)                              98% (228/232) Genotype 1a              92% (155/169)                               99% (170/172) Genotype 1b              97% (61/63)                                 97% (57/59) Genotype 2                97% (61/63)                                100% (53/53) Genotype 3                99% (91/92)                                97% (86/89) Genotype 4                94% (59/63)                                98% (56/57) Genotype 5                94% (17/18)                                0/0 Genotype 6                100% (30/30)                               100% (9/9) Outcome for patients without SVR
On-treatment virologic
0/501                                      0/440 failure
Relapsec                  4% (21/498)                                1% (3/439) Otherd                    1% (3/501)                                 1% (5/440) * 23% of patients enrolled into POLARIS-2 had received prior treatment with an interferon-based regimen.
a. Two patients with undetermined genotype in the SOF/VEL/VOX group achieved SVR12.
b. Two patients had genotype 1 subtypes other than genotype 1a or genotype 1b; both patients achieved SVR12.
c. The denominator for relapse is the number of patients with HCV RNA 
                
Pharmacokinetic Properties
                                
5.2   Pharmacokinetic properties
Absorption

The pharmacokinetic properties of sofosbuvir, GS-331007, velpatasvir and voxilaprevir have been evaluated in healthy adult subjects and in patients with chronic hepatitis C.

Sofosbuvir
Following oral administration of Vosevi, sofosbuvir was absorbed quickly and the peak median plasma concentration was observed 2 hours post-dose. Median peak plasma concentration of GS-331007 was observed 4 hours post-dose. Based on the population pharmacokinetic analysis in HCV-infected patients, mean steady-state AUC0-24 and Cmax for sofosbuvir (n = 1038) were 1665 ng•hr/mL and 678 ng/mL, respectively; mean steady-state AUC0-24 and Cmax for GS-331007 (n = 1593) were 12834 ng•hr/mL and 744 ng/mL, respectively. Sofosbuvir and GS-331007 AUC0-24 and Cmax were similar in healthy adult subjects and patients with HCV infection.

Velpatasvir
Velpatasvir median peak concentrations were observed at 4 hours post-dose. Based on the population pharmacokinetic analysis in HCV-infected patients mean steady-state AUC0-24 and Cmax for velpatasvir (n = 1595) were 4041 ng•hr/mL and 311 ng/mL, respectively. Relative to healthy subjects (n = 137), velpatasvir AUC0-24 and Cmax were 41% lower and 39% lower, respectively, in HCV-infected patients.

Voxilaprevir
Voxilaprevir median peak concentrations were observed 4 hours post-dose. Based on the population pharmacokinetic analysis in HCV-infected patients mean steady-state AUC0-24 and Cmax for voxilaprevir (n = 1591) were 2577 ng•hr/mL and 192 ng/mL, respectively. Relative to healthy subjects (n = 63), voxilaprevir AUC0-24 and Cmax were both 260% higher in HCV-infected patients.

Effects of food
When Vosevi or its components taken together were administered with food, sofosbuvir AUC0-inf and Cmax were 64% to 144% and 9% to 76% higher, respectively; velpatasvir AUC0-inf and Cmax were 40% to 166% and 37% to 187% higher, respectively; and voxilaprevir AUC0-inf and Cmax were 112% to 435% and 147% to 680% higher, respectively. GS-331007 AUC0-inf did not change and Cmax was 19% to 35% lower when Vosevi or its components together were administered with 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% 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 0.5 and 0.7.


Voxilaprevir is approximately > 99% bound to human plasma proteins. After a single 100 mg dose of [14C]-voxilaprevir in healthy subjects, the blood to plasma ratio of [14C]-radioactivity ranged between 0.5 and 0.8.

Biotransformation

Sofosbuvir is extensively metabolised in the liver to form the pharmacologically active nucleoside analogue 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. After a single 400 mg oral dose of [14C]-sofosbuvir, GS-331007 accounted for approximately > 90% of total systemic exposure.

Velpatasvir is primarily 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.

Voxilaprevir is primarily a substrate of CYP3A4 with slow turnover. Following a single dose of 100 mg [14C]-voxilaprevir, the majority (approximately 91%) of radioactivity in plasma was parent drug. The hydrolysed and dehydrogenated voxilaprevir were the major metabolites identified in human plasma. Unchanged voxilaprevir 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 Vosevi were 0.5 and 29 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 Vosevi was approximately 17 hours.

Following a single 100 mg oral dose of [14C]-voxilaprevir, mean total recovery of the [14C]-radioactivity was 94%, with all radioactivity measured in the faeces and none in the urine.
Unchanged voxilaprevir was the major species in faeces accounting for a mean of 40% of the administered dose. Voxilaprevir metabolites also identified in faeces included des- [methylcyclopropylsulphonamide]-voxilaprevir (22.1%), which is formed intestinally, dehydro- voxilaprevir (7.5%), and two des-[methylcyclopropylsulphonamide]-oxy-voxilaprevir metabolites (5.4% and 3.9%). Biliary excretion of parent drug was the major route of elimination for voxilaprevir.
The median terminal half-life of voxilaprevir following administration of Vosevi was approximately 33 hours.

Linearity/non-linearity

Sofosbuvir and GS-331007 AUCs are near dose-proportional over the dose range of 200 mg to 1200 mg. Velpatasvir AUC increases in a greater than proportional manner from 5 to 50 mg and in a less than proportional manner from 50 to 450 mg, indicating velpatasvir absorption is solubility limited. Voxilaprevir (studied under fed conditions) AUC increases in a greater than dose-proportional manner over the dose range of 100 to 900 mg.

In vitro potential for sofosbuvir/velpatasvir/voxilaprevir drug-drug interactions 
Sofosbuvir, velpatasvir and voxilaprevir are substrates of drug transporters P-gp and BCRP while GS-331007 is not. Voxilaprevir, and to a lesser extent velpatasvir, are also substrates of OATP1B1 and OATP1B3. In vitro, slow metabolic turnover of velpatasvir primarily by CYP2B6, CYP2C8, and CYP3A4 and of voxilaprevir primarily by CYP3A4 was observed.

Sofosbuvir and GS-331007 are not inhibitors of drug transporters P-gp, BCRP, multidrug resistance- associated protein 2 (MRP2), bile salt export pump (BSEP), OATP1B1, OATP1B3 and organic cation transporter (OCT) 1 and GS-331007 is not an inhibitor of OAT1, OAT3, OCT2, and multidrug and toxin extrusion protein (MATE) 1. Sofosbuvir and GS-331007 are not inhibitors or inducers of CYP or uridine glucuronosyltransferase (UGT) 1A1 enzymes.

Velpatasvir is an inhibitor of drug transporter P-gp, BCRP, OATP1B1, OATP1B3 and OATP2B1, and its involvement in drug interactions with these transporters is primarily limited to the process of absorption. At clinically relevant concentrations, velpatasvir is not an inhibitor of hepatic transporters BSEP, sodium taurocholate cotransporter protein (NTCP), OATP1A2 or OCT1, renal transporters OCT2, OAT1, OAT3, MRP2 or MATE1, or CYP or UGT1A1 enzymes.

Voxilaprevir is an inhibitor of drug transporters 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 concentrations, voxilaprevir is not an inhibitor of hepatic transporters OCT1, renal transporters OCT2, OAT1, OAT3 or MATE1, or CYP or UGT1A1 enzymes.

Pharmacokinetics in special populations

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

Elderly
Population pharmacokinetic analysis in HCV-infected patients showed that within the age range (18 to 85 years) analysed, age did not have a clinically relevant effect on the exposure to sofosbuvir, GS-331007, velpatasvir or voxilaprevir. In the 13 patients aged 75 to 84 years with available pharmacokinetic data, mean exposure to voxilaprevir was 93% higher than the mean exposure observed in patients aged 18 to 64 years.

Renal impairment
A summary of the effect of varying degrees of renal impairment (RI) on the exposures of the components of Vosevi compared to subjects with normal renal function, as described in the text below, are provided in Table 15.

Table 15: Effect of varying degrees of renal impairment on exposures (AUC) of SOF, GS- 331007, velpatasvir and voxilaprevir 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       (eGFR ≥30    (eGFR <30              Dialysis             (eGFR     Requiring ≥50 and       and <50    mL/min/1.73      Dosed 1     Dosed 1          <30      Dialysis <80       mL/min/1.73      m2)         hr Before    hr After      mL/min/1.
mL/min/1.        m2)                       Dialysis    Dialysis       73m2) 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↑ Voxilaprevir       -            -           1.7-fold↑        -            -           -            - 
The pharmacokinetics of sofosbuvir was studied in HCV negative 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 patients with severe renal impairment.

The pharmacokinetics of velpatasvir were studied with a single dose of 100 mg velpatasvir in HCV negative patients with severe renal impairment (eGFR < 30 mL/min by Cockcroft-Gault).
Voxilaprevir is not renally eliminated.
Additionally, the pharmacokinetics of voxilaprevir were studied with a single dose of 100 mg voxilaprevir in HCV negative patients with severe renal impairment (eGFR < 30 mL/min by Cockcroft-Gault). The pharmacokinetics of voxilaprevir have not been studied in subjects with ESRD requiring dialysis (see section 4.2).

The pharmacokinetics of sofosbuvir, GS-331007, and velpatasvir were studied in HCV-infected patients with ESRD requiring dialysis treated with once daily sofosbuvir/velpatasvir 400/100 mg for 12 weeks, and compared to patients without renal impairment in the sofosbuvir/velpatasvir Phase 2/3 trials.

Although exposures of the fixed-dose combination sofosbuvir, GS-331007, velpatasvir, and voxilaprevir were not directly evaluated in HCV-infected patients with ESRD requiring dialysis after administration of Vosevi, the exposures of sofosbuvir, GS-331007, and velpatasvir are expected to be similar to those observed after administration of sofosbuvir/velpatasvir 400/100 mg in HCV-infected patients with ESRD requiring dialysis.

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

The pharmacokinetics of velpatasvir were studied with a single dose of 100 mg velpatasvir in HCV negative patients with moderate and severe hepatic impairment (CPT Class B and C). Velpatasvir plasma exposure (AUCinf) was similar in patients with moderate hepatic impairment, severe hepatic impairment, and control subjects with normal hepatic function. Population pharmacokinetic analysis in HCV-infected patients indicated that cirrhosis (CPT Class A) had no clinically relevant effect on the exposure of velpatasvir.

The pharmacokinetics of voxilaprevir were studied with a single dose of 100 mg voxilaprevir in HCV negative patients with moderate and severe hepatic impairment (CPT Class B and C). Relative to patients with normal hepatic function, the voxilaprevir AUCinf was 299% and 500% higher in patients with moderate and severe hepatic impairment, respectively. The unbound fraction of voxilaprevir was approximately 2-fold higher in severe hepatic impairment compared with moderate hepatic impairment or normal hepatic function. Population pharmacokinetic analysis in HCV-infected 
patients indicated that patients with cirrhosis (CPT Class A) had 73% higher exposure of voxilaprevir than those without cirrhosis (see section 4.2).

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

Paediatric population
The pharmacokinetics of Vosevi in paediatric patients have not been established (see section 4.2).