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Sofosbuvir Tablets

TABLE OF CONTENTS

1. DESCRIPTION 8. USE IN SPECIFIC POPULATIONS
2. INDICATIONS AND USAGE 9. OVERDOSAGE
3. DOSAGE AND ADMINISTRATION 10. MECHANISM OF ACTION
4. CONTRAINDICATIONS 11. PHARMACODYNAMICS
5. WARNINGS AND PRECAUTIONS 12. PHARMACOKINETICS
6. ADVERSE REACTIONS 13. HOW SUPPLIED/STORAGE AND HANDLING
7. DRUG INTERACTIONS

 

1. DESCRIPTION

Sofosbuvir is a nucleotide analog inhibitor of HCV NS5B polymerase.

The IUPAC name for sofosbuvir is (S)-Isopropyl 2-((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2-yl)methoxy)-(phenoxy)phosphorylamino)propanoate. It has the following structural formula:

Empirical formula: C22H29FN3O9P - Molecular weight: 529.45

Sofosbuvir is a white to off-white crystalline solid with a solubility of ≥ 2 mg/mL across the pH range of 2-7.7 at 37 oC and is slightly soluble in water.

Sofosbuvir tablets are for oral administration. Each tablet contains 400 mg of sofosbuvir. The tablets include the following inactive ingredients: colloidal silicon dioxide, croscarmellose sodium, magnesium stearate, mannitol, and microcrystalline cellulose. The tablets are film-coated with a coating material containing the following inactive ingredients: polyethylene glycol, polyvinyl alcohol, talc, titanium dioxide, and yellow iron oxide.

2. INDICATIONS AND USAGE

Sofosbuvir is a hepatitis C virus (HCV) nucleotide analog NS5B polymerase inhibitor indicated for the treatment of chronic hepatitis C (CHC) infection as a component of a combination antiviral treatment regimen.

• Sofosbuvir efficacy has been established in subjects with HCV genotype 1, 2, 3 or 4 infection, including those with hepatocellular carcinoma meeting Milan criteria (awaiting liver transplantation) and those with HCV/HIV-1 co-infection [See Dosage and Administration (2), Use in Specific Populations (8)].

The following points should be considered when initiating treatment with sofosbuvir:

• Monotherapy of sofosbuvir is not recommended for treatment of CHC.

• Treatment regimen and duration are dependent on both viral genotype and patient population [See Dosage and Administration (2)].

• Treatment response varies based on baseline host and viral factors [See Use in Specific Populations (8)].

3. DOSAGE AND ADMINISTRATION

3.1 Recommended Dose in Adults

The recommended dose of sofosbuvir is one 400 mg tablet, taken orally, once daily with or without food.

Sofosbuvir should be used in combination with ribavirin or in combination with pegylated interferon and ribavirin for the treatment of CHC in adults. The recommended regimen and treatment duration for sofosbuvir combination therapy is provided in Table 1.

Table 1. Recommended Regimens and Treatment Duration for Sofosbuvir Combination Therapy in HCV Mono-infected and HCV/HIV-1 Coinfected Patients

a. See peginterferon alfa prescribing information for dosing recommendation for patients with genotype 1 or 4 CHC.

b. Dose of ribavirin is weight-based (<75 kg = 1000 mg and ≥75 kg = 1200 mg). The daily dose of ribavirin is administered orally in two divided doses with food. Patients with renal impairment (CrCl ≤ 50 mL/min) require ribavirin dose reduction; refer to ribavirin prescribing information.

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Sofosbuvir in combination with ribavirin for 24 weeks can be considered as a therapeutic option for CHC patients with genotype 1 infection who are ineligible to receive an interferon-based regimen [See Use in Specific Populations (8.8)]. Treatment decision should be guided by an assessment of the potential benefits and risks for the individual patient.

Patients with Hepatocellular Carcinoma Awaiting Liver Transplantation

Sofosbuvir in combination with ribavirin is recommended for up to 48 weeks or until the time of liver transplantation, whichever occurs first, to prevent post-transplant HCV reinfection [See Use in Specific Populations (8.9)].

3.2 Dose Modification

Dose reduction of sofosbuvir is not recommended.

Genotype 1 and 4:

If a patient has a serious adverse reaction potentially related to peginterferon alfa and/or ribavirin, the peginterferon alfa and/or ribavirin dose should be reduced or discontinued. Refer to the peginterferon alfa and ribavirin prescribing information for additional information about how to reduce and/or discontinue the peginterferon alfa and/or ribavirin dose.

Genotype 2 and 3:

If a patient has a serious adverse reaction potentially related to ribavirin, the ribavirin dose should be modified or discontinued, if appropriate, until the adverse reaction abates or decreases in severity. Table 2 provides guidelines for dose modifications and discontinuation based on the patient’s hemoglobin concentration and cardiac status.

Table 2. Ribavirin Dose Modification Guideline for Coadministration with Sofosbuvir

a. The daily dose of ribavirin is administered orally in two divided doses with food.

b. Once ribavirin has been withheld due to either a laboratory abnormality or clinical manifestation, an attempt may be made to restart ribavirin at 600 mg daily and further increase the dose to 800 mg daily. However, it is not recommended that ribavirin be increased to the original assigned dose (1000 mg to 1200 mg daily).

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3.3 Discontinuation of Dosing

If the other agents used in combination with sofosbuvir are permanently discontinued, sofosbuvir should also be discontinued.

3.4 Severe Renal Impairment and End Stage Renal Disease

No dose recommendation can be given for patients with severe renal impairment (estimated Glomerular Filtration Rate (eGFR) < 30 mL/min/1.73m2) or with end stage renal disease (ESRD) due to higher exposures (up to 20-fold) of the predominant sofosbuvir metabolite [See Use in Specific Populations (8.6)

4. CONTRAINDICATIONS

When sofosbuvir is used in combination with ribavirin or peginterferon alfa/ribavirin, the contraindications applicable to those agents are applicable to combination therapies. Refer to the prescribing information of peginterferon alfa and ribavirin for a list of their contraindications.

Sofosbuvir combination treatment with ribavirin or peginterferon alfa/ribavirin is contraindicated in women who are pregnant or may become pregnant and men whose female partners are pregnant because of the risks for birth defects and fetal death associated with ribavirin [See Warnings and Precautions (5.1) and Use in Specific Populations (8.1)].

5. WARNINGS AND PRECAUTIONS

5.1 Pregnancy: Use with Ribavirin or Peginterferon Alfa/Ribavirin

Ribavirin may cause birth defects and/or death of the exposed fetus and animal studies have shown that interferons have abortifacient effects [See Contraindications (4)]. Extreme care must be taken to avoid pregnancy in female patients and in female partners of male patients. Ribavirin therapy should not be started unless a report of a negative pregnancy test has been obtained immediately prior to initiation of therapy.

When sofosbuvir is used in combination with ribavirin or peginterferon alfa/ribavirin, women of childbearing potential and their male partners must use two forms of effective contraception during treatment and for at least 6 months after treatment has concluded. Routine monthly pregnancy tests must be performed during this time. There are no data on the effectiveness of systemic hormonal contraceptives in women taking sofosbuvir, therefore, two non-hormonal methods of contraception should be used during treatment with sofosbuvir and concomitant ribavirin [See Contraindications (4) and Use in Specific Populations (8.1)]. Refer also to the prescribing information for ribavirin.

5.2 Use with Potent P-gp Inducers

Drugs that are potent P-gp inducers in the intestine (e.g., rifampin, St. John’s wort) may significantly decrease sofosbuvir plasma concentrations and may lead to a reduced therapeutic effect of sofosbuvir. Rifampin and St. John’s wort should not be used with sofosbuvir [See Drug Interactions (7.2)].

6. ADVERSE REACTIONS

6.1 Adverse Reactions from Clinical Trials Experience

Sofosbuvir should be administered with ribavirin or peginterferon alfa/ribavirin. Refer to the prescribing information of peginterferon alfa and ribavirin for a description of adverse reactions associated with their use.

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The safety assessment of sofosbuvir is based on pooled Phase 3 clinical trial data (both controlled and uncontrolled) including 650 subjects who received sofosbuvir + ribavirin (RBV) combination therapy for 12 weeks, 98 subjects who received sofosbuvir + ribavirin combination therapy for 16 weeks, 250 subjects who received sofosbuvir + ribavirin combination therapy for 24 weeks, 327 subjects who received sofosbuvir + peginterferon (Peg-IFN) alfa + ribavirin combination therapy for 12 weeks, 243 subjects who received peginterferon alfa + ribavirin for 24 weeks and 71 subjects who received placebo (PBO) for 12 weeks.

The proportion of subjects who permanently discontinued treatment due to adverse events was 4% for subjects receiving placebo, 1% for subjects receiving sofosbuvir + ribavirin for 12 weeks, < 1% for subjects receiving sofosbuvir + ribavirin for 24 weeks, 11% for subjects receiving peginterferon alfa + ribavirin for 24 weeks and 2% for subjects receiving sofosbuvir + peginterferon alfa + ribavirin for 12 weeks.

Treatment-emergent adverse events observed in ≥15% of subjects in clinical trials are provided in Table 3. A side-by-side tabulation is to simplify presentation; direct comparison across trials should not be made due to differing trial designs.

The most common adverse events (≥ 20%) for sofosbuvir + ribavirin combination therapy were fatigue and headache. The most common adverse events (≥ 20%) for sofosbuvir + peginterferon alfa + ribavirin combination therapy were fatigue, headache, nausea, insomnia and anemia.

Table 3. Treatment-Emergent Adverse Events (All Grades) Reported in ≥ 15% of Subjects in Any Treatment Arm

a. Subjects received weight-based ribavirin (1000 mg per day if weighing < 75 kg or 1200 mg per day if weighing ≥ 75 kg).

b. Subjects received 800 mg ribavirin per day regardless of weight.

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With the exception of anemia and neutropenia, the majority of events presented in Table 3 occurred at severity of grade 1 in sofosbuvir-containing regimens.

Less Common Adverse Reactions Reported in Clinical Trials (<1%): The following ADRs occurred in < 1% of subjects receiving sofosbuvir in a combination regimen in any one trial. These events have been included because of their seriousness or assessment of potential causal relationship.

Hematologic Effects: pancytopenia (particularly in subjects receiving concomitant pegylated interferon).

Psychiatric Disorders: severe depression (particularly in subjects with pre-existing history of psychiatric illness), including suicidal ideation and suicide.

Laboratory Abnormalities:

Changes in selected hematological parameters are described in Table 4. A side-by-side tabulation is to simplify presentation; direct comparison across trials should not be made due to differing trial designs.

Table 4. Percentage of Subjects Reporting Selected Hematological Parameters

a. Subjects received weight-based ribavirin (1000 mg per day if weighing < 75 kg or 1200 mg per day if weighing ≥ 75 kg).

b. Subjects received 800 mg ribavirin per day regardless of weight.

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Bilirubin Elevations

Total bilirubin elevation of more than 2.5xULN was observed in none of the subjects in the sofosbuvir + peginterferon alfa + ribavirin 12 weeks group and in 1%, 3% and 3% of subjects in the peginterferon alfa + ribavirin 24 weeks, sofosbuvir + ribavirin 12 weeks and sofosbuvir + ribavirin 24 weeks groups, respectively. Bilirubin levels peaked during the first 1 to 2 weeks of treatment and subsequently decreased and returned to baseline levels by post-treatment Week 4. These bilirubin elevations were not associated with transaminase elevations.

Creatine Kinase Elevations

Creatine kinase was assessed in the FISSION and NEUTRINO trials. Isolated, asymptomatic creatine kinase elevation of greater than or equal to 10xULN was observed in <1%, 1% and 2% of subjects in the peginterferon alfa + ribavirin 24 weeks, sofosbuvir + peginterferon alfa + ribavirin 12 weeks and sofosbuvir + ribavirin 12 weeks groups, respectively.

Lipase Elevations

Isolated, asymptomatic lipase elevation of greater than 3xULN was observed in < 1%, 2%, 2%, and 2% of subjects in the sofosbuvir + peginterferon alfa + ribavirin 12 weeks, sofosbuvir + ribavirin 12 weeks, sofosbuvir + ribavirin 24 weeks and peginterferon alfa + ribavirin 24 weeks groups, respectively.

7. DRUG INTERACTIONS

7.1 Potential for Drug Interactions

After oral administration of sofosbuvir, sofosbuvir is rapidly converted to the predominant circulating metabolite GS-331007 that accounts for greater than 90% of drug related material systemic exposure, while the parent sofosbuvir accounts for approximately 4% of drug related material. In clinical pharmacology studies, both sofosbuvir and GS-331007 were monitored for purposes of pharmacokinetic analyses.

Sofosbuvir is a substrate of drug transporter P-gp and breast cancer resistance protein (BCRP) while GS-331007 is not. Drugs that are potent P-gp inducers in the intestine (e.g., rifampin or St. John’s wort) may decrease sofosbuvir plasma concentration leading to reduced therapeutic effect of sofosbuvir and thus should not be used with sofosbuvir [See Warnings and Precautions (5.2)]. Coadministration of sofosbuvir with drugs that inhibit P-gp and/or BCRP may increase sofosbuvir plasma concentration without increasing GS-331007 plasma concentration; accordingly, sofosbuvir may be coadministered with P-gp and/or BCRP inhibitors. Sofosbuvir and GS-331007 are not inhibitors of P-gp and BCRP and thus are not expected to increase exposures of drugs that are substrates of these transporters.

The intracellular metabolic activation pathway of sofosbuvir is mediated by generally low affinity and high capacity hydrolase and nucleotide phosphorylation pathways that are unlikely to be affected by concomitant drugs.

7.2 Potentially Significant Drug Interactions

Drug interaction information for sofosbuvir with potential concomitant drugs is summarized in Table 5. The drug interactions described are based on potential drug interactions that may occur with sofosbuvir. The table is not all-inclusive [See Warnings and Precautions (5.2)].

Table 5. Potentially Significant Drug Interactions: Alteration in Dose or Regimen May Be Recommended Based on Drug Interaction Studies or Predicted Interactiona

a. This table is not all inclusive.

b. ↓ = decrease.

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7.3 Drugs without Clinically Significant Interactions with Sofosbuvir

In addition to the drugs included in Table 5, the interaction between sofosbuvir and the following drugs was evaluated in clinical trials and no dose adjustment is needed for either drug: cyclosporine, darunavir/ritonavir, efavirenz, emtricitabine, methadone, raltegravir, rilpivirine, tacrolimus, or tenofovir disoproxil fumarate.

8. USE IN SPECIFIC POPULATIONS

8.1 Usage in Pregnancy

Pregnancy Category X: Use with Ribavirin or Peginterferon Alfa/Ribavirin

Extreme caution must be taken to avoid pregnancy in female patients and female partners of male patients while taking this combination. Women of childbearing potential and their male partners should not receive ribavirin unless they are using two forms of effective contraception during treatment with ribavirin and for 6 months after treatment has concluded. There are no data on the effectiveness of systemic hormonal contraceptives in women taking sofosbuvir. Therefore, two effective non-hormonal methods of contraception should be used during treatment with sofosbuvir and concomitant ribavirin [See Warnings and Precautions (5.1)].

In case of exposure during pregnancy, a Ribavirin Pregnancy Registry has been established to monitor maternal-fetal outcomes of pregnancies in female patients and female partners of male patients exposed to ribavirin during treatment and for 6 months following cessation of treatment. Healthcare providers and patients are encouraged to report such cases by calling Ribavirin Pregnancy Registry at 1800-593-2214. For patients who are HCV/HIV-1 co-infected and taking concomitant antiretrovirals, an Antiretroviral Pregnancy Registry is also available at 1-800-2584263.

Animal Data

Significant teratogenic and/or embryocidal effects have been demonstrated in all animal species exposed to ribavirin; and therefore ribavirin is contraindicated in women who are pregnant and in the male partners of women who are pregnant [See Contraindications (4), Warnings and Precautions (5.1) and ribavirin Package Insert]. Interferons have abortifacient effects in animals and should be assumed to have abortifacient potential in humans [See peginterferon alfa Package Insert].

Pregnancy Category B: Sofosbuvir

There are no adequate and well-controlled studies with sofosbuvir in pregnant women.

Animal Data

No effects on fetal development have been observed in rats and rabbits at the highest doses tested. In the rat and rabbit, AUC exposure to the predominant circulating metabolite GS-331007 increased over the course of gestation from approximately 5-to 10-fold and 12-to 28-fold the exposure in humans at the recommended clinical dose, respectively.

8.3 Nursing Mothers

It is not known whether sofosbuvir and its metabolites are present in human breast milk. The predominant circulating metabolite GS-331007 was the primary component observed in the milk of lactating rats, without effect on nursing pups. Because of the potential for adverse reactions from the drug in nursing infants, a decision must be made whether to discontinue nursing or discontinue treatment with ribavirin-containing regimens, taking into account the importance of the therapy to the mother. See also the prescribing information for ribavirin.

8.4 Pediatric Use

Safety and effectiveness of sofosbuvir in children less than 18 years of age have not been established.

8.5 Geriatric Use

Sofosbuvir was administered to 90 subjects aged 65 and over. The response rates observed for subjects over 65 years of age were similar to that of younger subjects across treatment groups. No dose adjustment of sofosbuvir is warranted in geriatric patients.

8.6 Renal Impairment

No dose adjustment of sofosbuvir is required for patients with mild or moderate renal impairment. The safety and efficacy of sofosbuvir have not been established in patients with severe renal impairment (eGFR < 30 mL/min/1.73m2) or end stage renal disease (ESRD) requiring hemodialysis. No dose recommendation can be given for patients with severe renal impairment or ESRD [See Dosage and Administration (3.4)]. Refer also to ribavirin and peginterferon alfa prescribing information for patients with CrCl < 50 mL/min.

8.7 Hepatic Impairment

No dose adjustment of sofosbuvir is required for patients with mild, moderate or severe hepatic impairment (Child-Pugh Class A, B or C). Safety and efficacy of sofosbuvir have not been established in patients with decompensated cirrhosis. See peginterferon alfa prescribing information for contraindication in hepatic decompensation.

8.8 Patients with HCV/HIV-1 Co-infection

The safety and efficacy of sofosbuvir was assessed in 223 HCV/HIV-1 co-infected subjects. See Dosage and Administration (3.1) for dosing recommendations in HCV/HIV-1 co-infected patients. The safety profile in HCV/HIV-1 co-infected subjects was similar to that observed in HCV mono-infected subjects. Elevated total bilirubin (grade 3 or 4) was observed in 30/32 (94%) subjects receiving atazanavir as part of the antiretroviral regimen. None of the subjects had concomitant transaminase increases. Among subjects not taking atazanavir, grade 3 or 4 elevated total bilirubin was observed in 2 (1.5%) subjects, similar to the rate observed with HCV mono-infected subjects receiving sofosbuvir + ribavirin in Phase 3 trials [See Adverse Reactions (6.1)].

8.9 Patients with Hepatocellular Carcinoma Awaiting Liver Transplantation

Sofosbuvir was studied in HCV-infected subjects with hepatocellular carcinoma prior to undergoing liver transplantation in an open-label clinical trial evaluating the safety and efficacy of sofosbuvir and ribavirin administered pre-transplant to prevent post-transplant HCV reinfection. The primary endpoint of the trial was post-transplant virologic response (pTVR) defined as HCV RNA < lower limit of quantification (LLOQ) at 12 weeks post-transplant. HCV-infected subjects, regardless of genotype, with hepatocellular carcinoma (HCC) meeting the MILAN criteria (defined as the presence of a tumor 5 cm or less in diameter in patients with single hepatocellular carcinomas and no more than three tumor nodules, each 3 cm or less in diameter in patients with multiple tumors and no extrahepatic manifestations of the cancer or evidence of vascular invasion of tumor) received 400 mg sofosbuvir and weight-based 1000-1200 mg ribavirin daily for 24-48 weeks or until the time of liver transplantation, whichever occurred first. An interim analysis was conducted on 61 subjects who received sofosbuvir and ribavirin; 45 subjects had HCV genotype 1; 44 subjects had a baseline CPT score less than 7 and all subjects had a baseline unadjusted MELD score ≤14. Of these 61 subjects, 41 subjects underwent liver transplantation following up to 48 weeks of treatment with sofosbuvir and ribavirin; 37 had HCV RNA < LLOQ at the time of transplantation. Of the 37 subjects, the post-transplant virologic response (pTVR) rate is 64% (23/36) in the 36 evaluable subjects who have reached the 12 week post-transplant time point. The safety profile of sofosbuvir and ribavirin in HCV-infected subjects prior to liver transplantation was comparable to that observed in subjects treated with sofosbuvir and ribavirin in Phase 3 clinical trials.

8.10 Post-Liver Transplant Patients

The safety and efficacy of sofosbuvir have not been established in post-liver transplant patients.

8.11 CHC Patients with Genotype 5 or 6 HCV Infection

Available data on subjects with genotype 5 or 6 HCV infection are insufficient for dosing recommendations.

9. OVERDOSAGE

The highest documented dose of sofosbuvir was a single supratherapeutic dose of sofosbuvir 1200 mg administered to 59 healthy subjects. In that trial, there were no untoward effects observed at this dose level, and adverse events were similar in frequency and severity to those reported in the placebo and sofosbuvir 400 mg treatment groups. The effects of higher doses are not known.

No specific antidote is available for overdose with sofosbuvir. If overdose occurs the patient must be monitored for evidence of toxicity. Treatment of overdose with sofosbuvir consists of general supportive measures including monitoring of vital signs as well as observation of the clinical status of the patient. A 4-hour hemodialysis session removed 18% of the administered dose.

10. MECHANISM OF ACTION

Sofosbuvir is an 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 analog 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 with IC50 values ranging from 0.7 to 2.6 μM. GS-461203 is not an inhibitor of human DNA and RNA polymerases nor an inhibitor of mitochondrial RNA polymerase.

Antiviral Activity

In HCV replicon assays, the EC50 values of sofosbuvir against full-length replicons from genotype 1a, 1b, 2a, 3a and 4a, and chimeric 1b replicons encoding NS5B from genotype 2b, 5a or 6a ranged from 0.014 to 0.11 μM. The median EC50 value of sofosbuvir against chimeric replicons encoding NS5B sequences from clinical isolates was 0.062 μM for genotype 1a (range 0.029-0.128 μM; N=67), 0.102 μM for genotype 1b (range 0.045-0.170 μM; N=29), 0.029 μM for genotype 2 (range 0.014-0.081 μM; N=15) and 0.081 μM for genotype 3a (range 0.024-0.181 μM; N=106). In infectious virus assays, the EC50 values of sofosbuvir against genotype 1a and 2a were 0.03 and 0.02 μM, respectively. The presence of 40% human serum had no effect on the anti-HCV activity of sofosbuvir. Evaluation of sofosbuvir in combination with interferon alpha or ribavirin 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. An M289L substitution developed along with the S282T substitution in genotype 2a, 5 and 6 replicons. Site-directed mutagenesis of the S282T substitution in replicons of 8 genotypes 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, recombinant NS5B polymerase from genotypes 1b, 2a, 3a and 4a expressing the S282T substitution showed reduced susceptibility to GS-461203 compared to respective wild-types.

In Clinical Trials

In a pooled analysis of 982 subjects who received sofosbuvir in Phase 3 trials, 224 subjects had post-baseline NS5B genotypic data from next generation nucleotide sequencing (assay cutoff of 1%).

Treatment-emergent substitutions L159F (n= 6) and V321A (n= 5) were detected in post-baseline samples from GT3a-infected subjects across the Phase 3 trials. No detectable shift in the phenotypic susceptibility to sofosbuvir of subject isolates with L159F or V321A substitutions was seen. The sofosbuvir-associated resistance substitution S282T was not detected at baseline or in the failure isolates from Phase 3 trials. However, an S282T substitution was detected in one genotype 2b subject who relapsed at Week 4 post-treatment after 12 weeks of sofosbuvir monotherapy in the Phase 2 trial P7977-0523 [ELECTRON]. The isolate from this subject displayed a mean 13.5-fold reduced susceptibility to sofosbuvir. For this subject, the S282T substitution was no longer detectable at Week 12 post-treatment by next generation sequencing with an assay cut off of 1%.

In the trial done in subjects with hepatocellular carcinoma awaiting liver transplantation where subjects received up to 48 weeks of sofosbuvir and ribavirin, the L159F substitution emerged in multiple subjects with GT1a or GT2b HCV who experienced virologic failure (breakthrough and relapse). Furthermore, the presence of substitutions L159F and/or C316N at baseline was associated with sofosbuvir breakthrough and relapse post-transplant in multiple subjects infected with GT1b HCV. In addition, S282R and L320F substitutions were detected on-treatment by next generation sequencing in a subject infected with GT1a HCV with a partial treatment response.

The clinical significance of these substitutions is not known.

11. PHARMACODYNAMICS

Effect on Electrocardiogram

The effect of sofosbuvir 400 and 1200 mg on QTc interval was evaluated in a randomized, single-dose, placebo-, and active-controlled (moxifloxacin 400 mg) four period crossover thorough QT trial in 59 healthy subjects. At a dose three times the maximum recommended dose, sofosbuvir does not prolong QTc to any clinically relevant extent.

12. PHARMACOKINETICS

Absorption

The pharmacokinetic properties of sofosbuvir and the predominant circulating metabolite GS-331007 have been evaluated in healthy adult subjects and in subjects with chronic hepatitis C. Following oral administration of sofosbuvir, sofosbuvir was absorbed with a peak plasma concentration observed at ~0.5-2 hour post-dose, regardless of dose level. Peak plasma concentration of GS-331007 was observed between 2 to 4 hours post-dose. Based on population pharmacokinetic analysis in subjects with genotype 1 to 6 HCV infection who were coadministered ribavirin (with or without pegylated interferon), geometric mean steady state sofosbuvir (N=838) and GS-331007 (N=1695) AUC0-24 were 828 ng•hr/mL and 6790 ng•hr/mL, respectively. Relative to healthy subjects administered sofosbuvir alone (N = 272), the sofosbuvir AUC0-24 was 39% higher and GS-331007 AUC0-24 was 39% lower, respectively, in HCV-infected subjects. Sofosbuvir and GS-331007 AUCs are near dose proportional over the dose range of 200 mg to 1200 mg.

Effect of Food

Relative to fasting conditions, the administration of a single dose of sofosbuvir with a standardized high fat meal did not substantially affect the sofosbuvir Cmax or AUC0-inf. The exposure of GS-331007 was not altered in the presence of a high-fat meal. Therefore, sofosbuvir 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.

Metabolism

Sofosbuvir is extensively metabolized 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 catalyzed 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, sofosbuvir and GS-331007 accounted for approximately 4% and >90% of drug related material (sum of molecular weight-adjusted AUC of sofosbuvir and its metabolites) systemic exposure, respectively.

Elimination

Following a single 400 mg oral dose of [14C]-sofosbuvir, mean total recovery of the dose was greater than 92%, consisting of approximately 80%, 14%, and 2.5% recovered in urine, feces, 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 were 0.4 and 27 hours, respectively.

Specific Populations

Race

Population pharmacokinetics analysis in HCV-infected subjects indicated that race had no clinically relevant effect on the exposure of sofosbuvir and GS-331007.

Gender

No clinically relevant pharmacokinetic differences have been observed between men and women for sofosbuvir and GS-331007.

Pediatric Patients

The pharmacokinetics of sofosbuvir in pediatric patients have not been established [See Use in Specific Populations (8.4)].

Geriatric Patients

Population pharmacokinetic analysis in HCV-infected subjects showed that within the age range (19 to 75 years) analyzed, age did not have a clinically relevant effect on the exposure to sofosbuvir and GS-331007 [See Use in Specific Populations (8.5)].

Patients with Renal Impairment

The pharmacokinetics of sofosbuvir were studied in HCV negative subjects with mild (eGFR ≥ 50 and < 80 mL/min/1.73m2), moderate (eGFR ≥30 and < 50 mL/min/1.73m2), severe renal impairment (eGFR < 30 mL/min/1.73m2) and subjects with end stage renal disease (ESRD) requiring hemodialysis following a single 400 mg dose of sofosbuvir. Relative to subjects with normal renal function (eGFR >80 mL/min/1.73m2), the sofosbuvir AUC0-inf was 61%, 107% and 171% higher in mild, moderate and severe renal impairment, while the GS-331007 AUC0-inf was 55%, 88% and 451% higher, respectively. In subjects with ESRD, relative to subjects with normal renal function, sofosbuvir and GS-331007 AUC0-inf was 28% and 1280% higher when sofosbuvir was dosed 1 hour before hemodialysis compared with 60% and 2070% higher when sofosbuvir was dosed 1 hour after hemodialysis, respectively. A 4 hour hemodialysis session removed approximately 18% of administered dose. No dose adjustment is required for patients with mild or moderate renal impairment. The safety and efficacy of sofosbuvir have not been established in patients with severe renal impairment or ESRD. No dose recommendation can be given for patients with severe renal impairment or ESRD [See Dosage and Administration (3.4) and Use in Specific Populations (8.6)].

Patients with Hepatic Impairment

The pharmacokinetics of sofosbuvir were studied following 7-day dosing of 400 mg sofosbuvir in HCV-infected subjects with moderate and severe hepatic impairment (Child-Pugh Class B and C). Relative to subjects with normal hepatic function, the sofosbuvir AUC0-24 were 126% and 143% higher in moderate and severe hepatic impairment, while the GS-331007 AUC0-24 were 18% and 9% higher, respectively. Population pharmacokinetics analysis in HCV-infected subjects indicated that cirrhosis had no clinically relevant effect on the exposure of sofosbuvir and GS-331007. No dose adjustment of sofosbuvir is recommended for patients with mild, moderate and severe hepatic impairment [See Use in Specific Populations (8.7)].

Assessment of Drug Interactions

The effects of coadministered drugs on the exposure of sofosbuvir and GS-331007 are shown in Table 6. The effects of sofosbuvir on the exposure of coadministered drugs are shown in Table 7 [See Drug Interactions (7.3)].

Table 6. Drug Interactions: Changes in Pharmacokinetic Parameters for Sofosbuvir and the Predominant Circulating Metabolite GS-331007 in the Presence of the Coadministered Druga

NA = not available/not applicable

a. All interaction studies conducted in healthy volunteers

b. Comparison based on historic control

c. Administered as ATRIPLA

______________________________________________________________

No effect on the pharmacokinetic parameters of sofosbuvir and GS-331007 was observed with raltegravir.

Table 7. Drug Interactions: Changes in Pharmacokinetic Parameters for Coadministered Drug in the Presence of Sofosbuvira

NA = not available/not applicable

a. All interaction studies conducted in healthy volunteers

b. Administered as ATRIPLA

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No effect on the pharmacokinetic parameters of the following coadministered drugs was observed with sofosbuvir: cyclosporine, darunavir/ritonavir, efavirenz, emtricitabine, methadone or rilpivirine.

13. HOW SUPPLIED/STORAGE AND HANDLING

1) How Available:

a) Brand name: SOVALDI, by Gilead Sciences.

b) Generic drugs: None.

2) How Supplied:

SOVALDI tablets are yellow, capsule-shaped, film-coated tablets containing 400 mg sofosbuvir debossed with “GSI” on one side and “7977” on the other side. Each bottle contains 28 tablets (NDC 61958-1501-1), a silica gel desiccant, polyester coil and is closed with a child-resistant closure.

3) Storage and Handling:

Store at room temperature below 30 °C (86 °F).

• Dispense only in original container

• Do not use if seal over bottle opening is broken or missing.

Rx only

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