Adverse Reactions in Adult Subjects with Chronic Hepatitis B and Compensated Liver Disease
The safety assessment of VEMLIDY was based on pooled data through the Week 96 data analysis from 1298 subjects in two randomized, double-blind, active-controlled trials, Trial 108 and Trial 110, in adult subjects with chronic hepatitis B and compensated liver disease. A total of 866 subjects received VEMLIDY 25 mg once daily [see Clinical Studies (14.2)]. Further safety assessment was based on pooled data from Trials 108 and 110 from subjects who continued to receive their original blinded treatment through Week 120 and additionally from subjects who received open-label VEMLIDY from Week 96 through Week 120 (n = 361 remained on VEMLIDY; n = 180 switched from TDF to VEMLIDY at Week 96).
Based on the Week 96 analysis, the most common adverse reaction (all Grades) reported in at least 10% of subjects in the VEMLIDY group was headache. The proportion of subjects who discontinued treatment with VEMLIDY or TDF due to adverse reactions of any severity was 1.5% and 0.9%, respectively. Table 1 displays the frequency of the adverse reactions (all Grades) greater than or equal to 5% in the VEMLIDY group.
Table 1 Adverse ReactionsFrequencies of adverse reactions are based on all treatment-emergent adverse events, regardless of relationship to study drug.
(All Grades) Reported in ≥5% of Subjects with Chronic HBV Infection and Compensated Liver Disease in Trials 108 and 110 (Week 96 analysisDouble-blind phase.
) | VEMLIDY (N=866) | TDF (N=432) |
|---|
| Headache | 12% | 10% |
| Abdominal pain Grouped term including abdominal pain upper, abdominal pain, abdominal pain lower, and abdominal tenderness. | 9% | 6% |
| Cough | 8% | 8% |
| Back pain | 6% | 6% |
| Fatigue | 6% | 5% |
| Nausea | 6% | 6% |
| Arthralgia | 5% | 6% |
| Diarrhea | 5% | 5% |
| Dyspepsia | 5% | 5% |
Additional adverse reactions occurring in less than 5% of subjects in Trials 108 and 110 included vomiting, rash, and flatulence.
The safety profile of VEMLIDY in subjects who continued to receive blinded treatment through Week 120 was similar to that at Week 96. The safety profile of VEMLIDY in subjects who remained on VEMLIDY in the open-label phase through Week 120 was similar to that in subjects who switched from TDF to VEMLIDY at Week 96.
Renal Laboratory Tests
In a pooled analysis of Trials 108 and 110 in adult subjects with chronic hepatitis B and a median baseline estimated creatinine clearance between 106 and 105 mL per minute (for the VEMLIDY and TDF groups, respectively), mean serum creatinine increased by less than 0.1 mg/dL and median serum phosphorus decreased by 0.1 mg/dL in both treatment groups at Week 96. Median change from baseline to Week 96 in estimated creatinine clearance was -1.2 mL per minute in the VEMLIDY group and -4.8 mL per minute in those receiving TDF.
In subjects who remained on blinded treatment beyond Week 96 in Trials 108 and 110, change from baseline in renal laboratory parameter values in each group at Week 120 were similar to those at Week 96. In the open-label phase, median change in estimated creatinine clearance by Cockcroft-Gault method from Week 96 to Week 120 was -0.6 mL per minute in subjects who remained on VEMLIDY and +1.8 mL per minute in those who switched from TDF to VEMLIDY at Week 96. Mean serum creatinine and median serum phosphorus values at Week 120 were similar to those at Week 96 in subjects who remained on VEMLIDY and in subjects who switched from TDF to VEMLIDY.
The long-term clinical significance of these renal laboratory changes on adverse reaction frequencies between VEMLIDY and TDF is not known.
Bone Mineral Density Effects
In a pooled analysis of Trials 108 and 110, the mean percentage change in bone mineral density (BMD) from baseline to Week 96 as assessed by dual-energy X-ray absorptiometry (DXA) was -0.7% with VEMLIDY compared to -2.6% with TDF at the lumbar spine and -0.3% compared to -2.5% at the total hip. BMD declines of 5% or greater at the lumbar spine were experienced by 11% of VEMLIDY subjects and 25% of TDF subjects at Week 96. BMD declines of 7% or greater at the femoral neck were experienced by 5% of VEMLIDY subjects and 13% of TDF subjects at Week 96.
In subjects who remained on blinded treatment beyond Week 96 in Trials 108 and 110, mean percentage change in BMD in each group at Week 120 was similar to that at Week 96. In the open-label phase, mean percentage change in BMD from Week 96 to Week 120 in subjects who remained on VEMLIDY was 0.6% at the lumbar spine and 0% at the total hip, compared to 1.7% at the lumbar spine and 0.6% at the total hip in those who switched from TDF to VEMLIDY.
The long-term clinical significance of these BMD changes is not known.
Laboratory Abnormalities
The frequency of laboratory abnormalities (Grades 3–4) occurring in at least 2% of subjects receiving VEMLIDY in Trials 108 and 110 are presented in Table 2.
Table 2 Laboratory Abnormalities (Grades 3–4) Reported in ≥2% of Subjects with Chronic HBV Infection and Compensated Liver Disease in Trials 108 and 110 (Week 96 analysisDouble-blind phase.
)| Laboratory Parameter Abnormality Frequencies are based on treatment-emergent laboratory abnormalities. | VEMLIDY (N=866) | TDF (N=432) |
|---|
| ULN=Upper Limit of Normal |
| ALT (>5 × ULN) | 8% | 10% |
| LDL-cholesterol (fasted) (>190 mg/dL) | 6% | 1% |
| Glycosuria (≥3+) | 5% | 2% |
| AST (>5 × ULN) | 3% | 5% |
| Creatine Kinase (≥10 × ULN) | 3% | 3% |
| Serum Amylase (>2.0 × ULN) | 3% | 3% |
The overall incidence of blinded treatment ALT flares (defined as confirmed serum ALT greater than 2 × baseline and greater than 10 × ULN at 2 consecutive postbaseline visits, with or without associated symptoms) was similar between VEMLIDY (0.6%) and TDF (0.9%) through Week 96. ALT flares generally were not associated with coincident elevations in bilirubin, occurred within the first 12 weeks of treatment, and resolved without recurrence.
Based on the Week 120 analysis, the frequencies of lab abnormalities in subjects who remained on VEMLIDY in the open-label phase were similar to those in subjects who switched from TDF to VEMLIDY at Week 96.
Amylase and Lipase Elevations and Pancreatitis
At Week 96, in Trials 108 and 110, eight subjects treated with VEMLIDY with elevated amylase levels had associated symptoms, such as nausea, low back pain; abdominal tenderness, pain, and distension; and biliary pancreatitis and pancreatitis. Of these eight, two subjects discontinued VEMLIDY due to elevated amylase and/or lipase; one subject experienced recurrence of adverse events when VEMLIDY was restarted. No subject treated with TDF had associated symptoms or discontinued treatment.
From Week 96 to Week 120, one additional subject who continued open-label VEMLIDY and none of the subjects who switched from TDF to VEMLIDY had elevated amylase levels and associated symptoms.
Serum Lipids
Changes from baseline in total cholesterol, HDL-cholesterol, LDL-cholesterol, triglycerides, and total cholesterol to HDL ratio among subjects treated with VEMLIDY and TDF in Trials 108 and 110 are presented in Table 3.
Table 3 Lipid Abnormalities: Mean Change from Baseline in Lipid Parameters in Patients with Chronic HBV Infection and Compensated Liver Disease in Trials 108 and 110 (Week 96 analysis) | VEMLIDY (N=866) | TDF (N=432) |
|---|
| Baseline | Week 96 | Baseline | Week 96 |
|---|
| mg/dL | Change The change from baseline is the mean of within-subject changes from baseline for subjects with both baseline and Week 96 values. | mg/dL | Change |
|---|
| Total Cholesterol (fasted) | 188 [n=835] | -1 [n=742] | 193 [n=423] | -25 [n=368] |
| HDL-Cholesterol (fasted) | 60 [n=835] | -5 [n=740] | 61 [n=423] | -12 [n=368] |
| LDL-Cholesterol (fasted) | 116 [n=835] | +7 [n=741] | 120 [n=423] | -10 [n=368] |
| Triglycerides (fasted) | 102 [n=836] | +13 [n=743] | 102 [n=423] | -7 [n=368] |
| Total Cholesterol to HDL ratio | 3 [n=835] | 0 [n=740] | 3 [n=423] | 0 [n=368] |
In the open-label phase, lipid parameters at Week 120 in subjects who remained on VEMLIDY were similar to those at Week 96. In subjects who switched from TDF to VEMLIDY, mean change from Week 96 to Week 120 in total cholesterol was 23 mg/dL, HDL-cholesterol was 5 mg/dL, LDL-cholesterol was 16 mg/dL, triglycerides was 30 mg/dL, and total cholesterol to HDL ratio was 0 mg/dL.
Adverse Reactions in Virologically Suppressed Adult Subjects with Chronic Hepatitis B
The safety of VEMLIDY in virologically suppressed adults is based on Week 48 data from a randomized, double-blind, active-controlled trial (Trial 4018) in which subjects taking TDF at baseline were randomized to switch to VEMLIDY (N=243) or to continue their TDF treatment (N=245). Adverse reactions observed with VEMLIDY in Trial 4018 were similar to those in Trials 108 and 110 [see Clinical Studies (14.3)].
Renal Laboratory Tests, Bone Mineral Density Effects, and Serum Lipids
In virologically suppressed adults in Trial 4018, changes from baseline in renal function, BMD, and lipid parameters in the VEMLIDY and TDF groups at Week 48 were similar to those observed in Trials 108 and 110 at Week 96.
Adverse Reactions in Adult Subjects with Chronic Hepatitis B and Renal Impairment
In an open-label trial (Trial 4035) in virologically suppressed adult subjects with chronic hepatitis B switching to VEMLIDY 25 mg, the safety of VEMLIDY was assessed in 78 subjects with moderate to severe renal impairment (estimated creatinine clearance between 15 and 59 mL per minute by Cockcroft-Gault method; Part A, Cohort 1) and 15 subjects with ESRD (estimated creatinine clearance below 15 mL per minute) receiving chronic hemodialysis (Part A, Cohort 2). The safety of VEMLIDY, including changes from baseline in renal function, BMD, and lipid parameters, was similar to that observed in clinical trials of VEMLIDY in subjects with compensated liver disease but without renal impairment [see Use in Specific Populations (8.6) and Clinical Studies (14.4)].
Pregnancy Exposure Registry
There is a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to VEMLIDY during pregnancy. Healthcare providers are encouraged to register patients by calling the Antiretroviral Pregnancy Registry (APR) at 1-800-258-4263.
Risk Summary
Available data from the APR show no significant difference in the overall risk of birth defects for tenofovir alafenamide (TAF) compared with the background rate for major birth defects of 2.7% in the U.S. reference population of the Metropolitan Atlanta Congenital Defects Program (MACDP) (see Data). The rate of miscarriage is not reported in the APR. The estimated background rate of miscarriage in clinically recognized pregnancies in the U.S. general population is 15% to 20%.
In animal studies, no adverse developmental effects were observed when tenofovir alafenamide was administered during the period of organogenesis at exposure equal to or 51 times (rats and rabbits, respectively) the tenofovir alafenamide exposure at the recommended daily dose of VEMLIDY (see Data). No adverse effects were observed in the offspring when TDF was administered through lactation at tenofovir exposures of approximately 12 times the exposure at the recommended daily dosage of VEMLIDY.
Data
Human Data
Based on prospective reports to the APR of exposures to TAF-containing regimens during pregnancy resulting in live births (including over 200 exposed in the first trimester and over 80 exposed in the second/third trimester), the prevalence of birth defects in live births was 5.2% (95% CI: 2.7% to 8.8%) and 1.2% (95% CI: 0% to 6.5%) following first and second/third trimester exposure, respectively, to TAF-containing regimens. Methodologic limitations of the APR include the use of MACDP as the external comparator group. The MACDP population is not disease-specific, evaluates women and infants from a limited geographic area, and does not include outcomes for births that occurred at <20 weeks gestation.
Animal Data
Embryonic fetal development studies performed in rats and rabbits revealed no evidence of impaired fertility or harm to the fetus. The embryo-fetal NOAELs (no observed adverse effect level) in rats and rabbits occurred at tenofovir alafenamide exposures similar to and 51 times higher than, respectively, the exposure in humans at the recommended daily dose. Tenofovir alafenamide is rapidly converted to tenofovir; the observed tenofovir exposure in rats and rabbits were 54 (rats) and 85 (rabbits) times higher than human tenofovir exposures at the recommended daily dose.
Tenofovir alafenamide was administered orally to pregnant rats (25, 100, or 250 mg/kg/day) and rabbits (10, 30, or 100 mg/kg/day) through organogenesis (on gestation days 6 through 17, and 7 through 20, respectively). No adverse embryo-fetal effects were observed in rats and rabbits at tenofovir alafenamide exposures approximately similar to (rats) and 51 (rabbits) times higher than the exposure in humans at the recommended daily dose of VEMLIDY. Tenofovir alafenamide is rapidly converted to tenofovir; the observed tenofovir exposures in rats and rabbits were 54 (rats) and 85 (rabbits) times higher than human tenofovir exposures at the recommended daily dose. Since tenofovir alafenamide is rapidly converted to tenofovir and a lower tenofovir exposure in rats and mice was observed after tenofovir alafenamide administration compared to TDF, another prodrug for tenofovir administration, a pre/postnatal development study in rats was conducted only with TDF. Doses up to 600 mg/kg/day were administered through lactation; no adverse effects were observed in the offspring on gestation day 7 [and lactation day 20] at tenofovir exposures of approximately 12 [18] times higher than the exposures in humans at the recommended daily dose of VEMLIDY.
Risk Summary
It is not known whether VEMLIDY and its metabolites are present in human breast milk, affect human milk production, or have effects on the breastfed infant. Tenofovir has been shown to be present in the milk of lactating rats and rhesus monkeys after administration of TDF (see Data). It is not known if tenofovir alafenamide can be present in animal milk. The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for VEMLIDY and any potential adverse effects on the breastfed infant from VEMLIDY or from the underlying maternal condition.
Data
Animal Data
Studies in rats and monkeys have demonstrated that tenofovir is secreted in milk. Tenofovir was excreted into the milk of lactating rats following oral administration of TDF (up to 600 mg/kg/day) at up to approximately 24% of the median plasma concentration in the highest dosed animals at lactation day 11 (see Data 8.1). Tenofovir was excreted into the milk of lactating monkeys following a single subcutaneous (30 mg/kg) dose of tenofovir at concentrations up to approximately 4% of plasma concentration, resulting in exposure (AUC) of approximately 20% of plasma exposure.
Cardiac Electrophysiology
In a thorough QT/QTc study in 48 healthy subjects, tenofovir alafenamide at the recommended dose or at a dose 5 times the recommended dose did not affect the QT/QTc interval and did not prolong the PR interval.
Specific Populations
Geriatric Patients, Race, and Gender
Limited data in subjects aged 65 years and over suggest a lack of clinically relevant differences in tenofovir alafenamide or tenofovir pharmacokinetics. No clinically relevant differences in tenofovir alafenamide or tenofovir pharmacokinetics due to race or gender have been identified [see Use in Specific Populations (8.5)].
Patients with Renal Impairment
In a Phase 1, open-label study, tenofovir alafenamide and tenofovir systemic exposures (AUCinf) were evaluated in subjects with severe renal impairment and in subjects with normal renal function (Table 7). In an open-label trial of elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide 150/150/200/10 mg, tenofovir alafenamide and tenofovir AUC were evaluated in a subset of virologically suppressed HIV-1 infected subjects with ESRD receiving chronic hemodialysis (Table 7). In a Phase 2, open-label trial, tenofovir alafenamide and tenofovir AUC were evaluated in a subset of virologically suppressed HBV-infected subjects with ESRD receiving chronic hemodialysis (Table 7) [see Use in Specific Populations (8.6)]. The pharmacokinetics of tenofovir alafenamide were similar among subjects with normal renal function, subjects with severe renal impairment, and subjects with ESRD receiving chronic hemodialysis. Relative to those with normal renal function, increased tenofovir exposures were observed in subjects with severe renal impairment and subjects with ESRD receiving chronic hemodialysis. Within the chronic hemodialysis population, increased tenofovir exposures were observed in subjects with HBV relative to those with HIV.
Table 7 Pharmacokinetics of Tenofovir Alafenamide and its Metabolite Tenofovir in Subjects with Renal Impairment as Compared to Subjects with Normal Renal Function| Estimated Creatinine Clearance By Cockcroft-Gault method. Mean (CV%) | ≥90 mL per minute 25 mg TAF (N=13)PK assessed on a single dose of TAF 25 mg in subjects with normal renal function and in subjects with severe renal impairment. | 15–29 mL per minute 25 mg TAF (N=14) | <15 mL per minute 25 mg TAFPK assessed on the day prior to hemodialysis of TAF 25 mg. These subjects from Study 4035 had a median baseline eGFR by Cockcroft-Gault of 7.2 mL/min (range, 4.8 to 12.0). (N=5) | <15 mL per minute 10 mg TAFExposures from TAF 25 mg = exposures from TAF 10 mg as part of elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide. PK assessed on the day prior to hemodialysis following 3 consecutive daily doses of elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide. These subjects from Study 1825 had a median baseline eGFR by Cockcroft-Gault of 10.2 mL/min (range, 6.8 to 19.2) . (N=12) |
|---|
| CV = coefficient of variation |
| Tenofovir alafenamide | |
| AUC (mcg∙hour per mL) | 0.27 (49.2) AUCinf. | 0.51 (47.3) | 0.30 (26.7) AUClast. | 0.23 (53.2) |
| Cmax (mcg per mL) | 0.20 (62.1) | 0.36 (65.7) | 0.23 (48.4) | 0.25 (75.4) |
| Tenofovir | |
| AUC (mcg∙hour per mL) | 0.34 (27.2) | 2.07 (47.1) | 18.8 (30.4) AUCtau. | 8.72 (39.4), N=10. |
| Cmax (mcg per mL) | 0.01 (36.5) | 0.03 (32.4) | 0.89 (26.4) | 0.44 (40.9) |
| C24h (mcg per mL) | 0.004 (25.6) | 0.02 (41.9) | 0.89 (26.4) | 0.26 (73.2) |
Patients with Hepatic Impairment
Tenofovir alafenamide and tenofovir pharmacokinetics are similar in subjects with mild (Child-Pugh Class A) hepatic impairment and in subjects with normal hepatic function.
HIV and/or Hepatitis C Virus Coinfection
The pharmacokinetics of tenofovir alafenamide have not been fully evaluated in subjects coinfected with HIV and/or hepatitis C virus.
Drug Interaction Studies
[see Drug Interactions (7)]
The effects of coadministered drugs on the exposure of tenofovir alafenamide are shown in Table 8. The effects of tenofovir alafenamide on the exposure of coadministered drugs are shown in Table 9 [For information regarding clinical recommendations, see Drug Interactions (7)]. Information regarding potential drug-drug interactions with HIV antiretrovirals is not provided (see the prescribing information for emtricitabine/tenofovir alafenamide for interactions with HIV antiretrovirals).
Table 8 Drug Interactions: Changes in Pharmacokinetic Parameters for Tenofovir Alafenamide in the Presence of the Coadministered DrugAll interaction studies conducted in healthy subjects.
| Coadministered Drug | Dose of Coadministered Drug (mg) | Tenofovir Alafenamide (mg) | N | Geometric Mean Ratio of TAF Pharmacokinetic Parameters (90% CI) All no effect boundaries are 70%–143%. ; No effect = 1.00 |
|---|
| Cmax | AUC | Cmin |
|---|
| NC = not calculated |
| Carbamazepine | 300 twice daily | 25 once daily Study conducted with emtricitabine/tenofovir alafenamide. | 26 | 0.43 (0.36, 0.51) | 0.45 (0.40, 0.51) | NC |
| Cobicistat A representative inhibitor of P-glycoprotein. | 150 once daily | 8 once daily | 12 | 2.83 (2.20, 3.65) | 2.65 (2.29, 3.07) | NC |
| Ledipasvir/ Sofosbuvir | 90/400 once daily | 25 once daily Study conducted with emtricitabine/rilpivirine/tenofovir alafenamide. | 42 | 1.03 (0.94, 1.14) | 1.32 (1.25, 1.40) | NC |
| Sertraline | 50 single dose | 10 once daily Study conducted with elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide. | 19 | 1.00 (0.86, 1.16) | 0.96 (0.89, 1.03) | NC |
| Sofosbuvir/ Velpatasvir/ Voxilaprevir | 400/100/100+ 100 voxilaprevir Study conducted with additional voxilaprevir 100 mg to achieve voxilaprevir exposures expected in HCV-infected patients. once daily | 25 once daily | 30 | 1.32 (1.17, 1.48) | 1.52 (1.43, 1.61) | NC |
Table 9 Drug Interactions: Changes in Pharmacokinetic Parameters for Coadministered Drug in the Presence of Tenofovir AlafenamideAll interaction studies conducted in healthy subjects.
| Coadministered Drug | Dose of Coadministered Drug (mg) | Tenofovir Alafenamide (mg) | N | Geometric Mean Ratio of Coadministered Drug Pharmacokinetic Parameters (90% CI) All no effect boundaries are 70%–143%. ; No effect = 1.00 |
|---|
| Cmax | AUC | Cmin |
|---|
| NC = not calculated |
| Ledipasvir | 90 ledipasvir / 400 sofosbuvir once daily | 25 once daily Study conducted with emtricitabine/rilpivirine/tenofovir alafenamide. | 41 | 1.01 (0.97, 1.05) | 1.02 (0.97, 1.06) | 1.02 (0.98, 1.07) |
| Sofosbuvir | 0.96 (0.89, 1.04) | 1.05 (1.01, 1.09) | NC |
| GS-331007 The predominant circulating nucleoside metabolite of sofosbuvir. | 1.08 (1.05, 1.11) | 1.08 (1.06, 1.10) | 1.10 (1.07, 1.12) |
| Midazolam A sensitive CYP3A4 substrate. | 2.5 single dose orally | 25 once daily | 18
| 1.02 (0.92, 1.13) | 1.13 (1.04, 1.23) | NC |
| 1 single dose IV | 0.99 (0.89, 1.11) | 1.08 (1.04, 1.14) | NC |
| Norelgestromin | norgestimate 0.180/0.215/0.250 once daily / ethinyl estradiol 0.025 once daily | 25 once daily Study conducted with emtricitabine/tenofovir alafenamide. | 29 | 1.17 (1.07, 1.26) | 1.12 (1.07, 1.17) | 1.16 (1.08, 1.24) |
| Norgestrel | 1.10 (1.02, 1.18) | 1.09 (1.01, 1.18) | 1.11 (1.03, 1.20) |
| Ethinyl estradiol | 1.22 (1.15, 1.29) | 1.11 (1.07, 1.16) | 1.02 (0.93, 1.12) |
| Sertraline | 50 single dose | 10 once daily Study conducted with elvitegravir/cobicistat/emtricitabine/tenofovir alafenamide. | 19 | 1.14 (0.94, 1.38) | 0.93 (0.77, 1.13) | NC |
| Sofosbuvir | 400 once daily | 25 once daily Study conducted with emtricitabine/rilpivirine/tenofovir alafenamide. | 30 | 0.95 (0.86, 1.05) | 1.01 (0.97, 1.06) | NC |
| GS-331007 | 1.02 (0.98, 1.06) | 1.04 (1.01, 1.06) | NC |
| Velpatasvir | 100 once daily | 1.05 (0.96, 1.16) | 1.01 (0.94, 1.07) | 1.01 (0.95, 1.09) |
| Voxilaprevir | 100+100 Study conducted with additional voxilaprevir 100 mg to achieve voxilaprevir exposures expected in HCV-infected patients. once daily | 0.96 (0.84, 1.11) | 0.94 (0.84, 1.05) | 1.02 (0.92, 1.12) |
Mechanism of Action
Tenofovir alafenamide is a phosphonamidate prodrug of tenofovir (2'-deoxyadenosine monophosphate analog). Tenofovir alafenamide as a lipophilic cell-permeant compound enters primary hepatocytes by passive diffusion and by the hepatic uptake transporters OATP1B1 and OATP1B3. Tenofovir alafenamide is then converted to tenofovir through hydrolysis primarily by carboxylesterase 1 (CES1) in primary hepatocytes. Intracellular tenofovir is subsequently phosphorylated by cellular kinases to the pharmacologically active metabolite tenofovir diphosphate. Tenofovir diphosphate inhibits HBV replication through incorporation into viral DNA by the HBV reverse transcriptase, which results in DNA chain-termination.
Tenofovir diphosphate is a weak inhibitor of mammalian DNA polymerases that include mitochondrial DNA polymerase γ and there is no evidence of toxicity to mitochondria in cell culture.
Antiviral Activity in Cell Culture
The antiviral activity of tenofovir alafenamide was assessed in a transient transfection assay using HepG2 cells against a panel of HBV clinical isolates representing genotypes A-H. The EC50 (50% effective concentration) values for tenofovir alafenamide ranged from 34.7 to 134.4 nM, with an overall mean EC50 value of 86.6 nM. The CC50 (50% cytotoxicity concentration) values in HepG2 cells were greater than 44,400 nM. In cell culture combination antiviral activity studies of tenofovir with the HBV nucleoside reverse transcriptase inhibitors entecavir, lamivudine, and telbivudine, no antagonistic activity was observed.
Resistance in Clinical Trials
Genotypic resistance analysis was performed on paired baseline and on-treatment HBV isolates for subjects who either experienced virologic breakthrough (2 consecutive visits with HBV DNA greater than or equal to 69 IU/mL [400 copies/mL] after having been less than 69 IU/mL, or 1.0-log10 or greater increase in HBV DNA from nadir) through Week 48, or had HBV DNA greater than or equal to 69 IU/mL at early discontinuation at or after Week 24.
In a pooled analysis of treatment-naïve and treatment-experienced subjects receiving VEMLIDY in Trials 108 and 110 [see Clinical Studies (14.2)], treatment-emergent amino acid substitutions in the HBV reverse transcriptase domain, all occurring at polymorphic positions, were observed in some HBV isolates evaluated (5/20); however, no specific substitutions occurred at a sufficient frequency to be associated with resistance to VEMLIDY.
In virologically suppressed subjects receiving VEMLIDY in Trial 4018 [see Clinical Studies (14.3)], no subjects qualified for resistance analysis through 48 weeks of VEMLIDY treatment.
Cross-Resistance
The antiviral activity of tenofovir alafenamide was evaluated against a panel of isolates containing substitutions associated with HBV nucleoside reverse transcriptase inhibitor resistance in a transient transfection assay using HepG2 cells. HBV isolates expressing the lamivudine resistance-associated substitutions rtM204V/I (±rtL180M±rtV173L) and expressing the entecavir resistance-associated substitutions rtT184G, rtS202G, or rtM250V in the presence of rtL180M and rtM204V showed less than 2-fold reduced susceptibility (within the inter-assay variability) to tenofovir alafenamide. HBV isolates expressing the rtA181T, rtA181V, or rtN236T single substitutions associated with resistance to adefovir also had less than 2-fold changes in EC50 values; however, the HBV isolate expressing the rtA181V plus rtN236T double substitutions exhibited reduced susceptibility (3.7-fold) to tenofovir alafenamide. The clinical relevance of these substitutions is not known.
Severe Acute Exacerbation of Hepatitis after Discontinuation of Treatment
Inform patients that discontinuation of anti-hepatitis B therapy, including VEMLIDY, may result in severe acute exacerbations of hepatitis B. Advise the patient to not discontinue VEMLIDY without first informing their healthcare provider [see Warnings and Precautions (5.1)].
Risk of Development of HIV-1 Resistance in Patients with HIV-1 Coinfection
Inform patients that if they have or develop HIV infection and are not receiving effective HIV treatment, VEMLIDY may increase the risk of development of resistance to HIV medication [see Dosage and Administration (2.1) and Warnings and Precautions (5.2)].
New Onset or Worsening Renal Impairment
Postmarketing cases of renal impairment, including acute renal failure, have been reported [see Warnings and Precautions (5.3)].
Lactic Acidosis and Severe Hepatomegaly
Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases, have been reported with use of drugs similar to VEMLIDY. Advise patients to contact their healthcare provider immediately and stop VEMLIDY if they develop clinical symptoms suggestive of lactic acidosis or pronounced hepatotoxicity [see Warnings and Precautions (5.4)].
Drug Interactions
Advise patients to report to their healthcare provider the use of any other prescription or non-prescription medication or herbal products including St. John's wort, as VEMLIDY may interact with other drugs [see Drug Interactions (7)].
Missed Dosage
Inform patients that it is important to take VEMLIDY on a regular dosing schedule with food and to avoid missing doses, as it can result in development of resistance [see Dosage and Administration (2.2)].
Pregnancy Registry
Inform patients that there is an antiretroviral pregnancy registry to monitor fetal outcomes of pregnant women exposed to VEMLIDY [see Use in Specific Populations (8.1)].
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