Sofosbuvir/Velpatasvir

Introduction Overview

Generic Name

sofosbuvir/velpatasvir

Brand Name

Epclusa

Dosage Form

oral pellet (150 mg-37.5 mg; 200 mg-50 mg), oral tablet (200 mg-50 mg; 400 mg-100 mg)

Drug Class

Antiviral combinations

Pharmacokinetics

Absorption:
Sofosbuvir/velpatasvir (Epclusa) exhibits good oral bioavailability with rapid absorption following oral administration. Sofosbuvir reaches peak plasma concentrations approximately 0.5 to 2 hours post-dose, while velpatasvir peaks around 3 hours. Food intake has minimal clinically significant effect on the pharmacokinetics of the combined formulation, permitting administration with or without food. The oral pellet formulation is designed for pediatric populations and allows swallowing without chewing, maintaining adequate systemic absorption.

Distribution:
Sofosbuvir demonstrates extensive tissue distribution, with a volume of distribution approximating 87 liters. Velpatasvir is highly protein bound (>99.5%), primarily to albumin, which influences its distribution profile. Both components distribute efficiently to the liver, the primary site of hepatitis C virus replication. Sofosbuvir’s active metabolite, GS-461203, accumulates intracellularly in hepatocytes, enabling targeted antiviral activity.

Metabolism:
Sofosbuvir is a nucleotide prodrug that undergoes extensive intracellular metabolism to form its pharmacologically active uridine analogue triphosphate, GS-461203. Metabolism involves initial hydrolysis and subsequent phosphorylation steps principally mediated by hepatic enzymes, including CES1 and HINT1. Velpatasvir is metabolized primarily by cytochrome P450 isoenzymes CYP2B6, CYP2C8, and CYP3A4. These metabolic pathways are significant as coadministered drugs that modulate CYP enzyme activity may alter velpatasvir plasma levels and clinical efficacy.

Elimination:
Sofosbuvir is eliminated predominantly via renal excretion of its inactive metabolite GS-331007 (>80%) with a terminal half-life of approximately 27 hours. Velpatasvir is eliminated mainly via feces (approximately 94%) with a terminal half-life of around 15 hours. Less than 1% of velpatasvir is excreted renally. Impaired renal function, especially severe impairment or patients on dialysis, may increase exposure to sofosbuvir metabolites, necessitating careful clinical monitoring. Hepatic impairment can affect metabolism and elimination, but Epclusa is approved for use in compensated cirrhosis with dosage modifications advised depending on severity.

Dosage Forms

Available Dosage Forms:
- Oral tablets: 400 mg sofosbuvir and 100 mg velpatasvir; 200 mg sofosbuvir and 50 mg velpatasvir.
- Oral pellets: 200 mg sofosbuvir and 50 mg velpatasvir; 150 mg sofosbuvir and 37.5 mg velpatasvir.

Dosages for Adults and Adolescents:
- Adults (≥18 years): One tablet containing 400 mg sofosbuvir and 100 mg velpatasvir orally once daily for 12 weeks is the standard regimen for patients with chronic hepatitis C genotypes 1–6, including those with compensated cirrhosis (Child-Pugh A).
- For patients with decompensated cirrhosis (Child-Pugh B or C), Epclusa is combined with ribavirin for 12 weeks.
- Adolescents and children ≥6 years:
* Weight 17 to <30 kg: Oral pellets or tablets containing 200 mg sofosbuvir and 50 mg velpatasvir once daily for 12 weeks.
* Weight ≥30 kg: Adult dosing applies, 400 mg/100 mg once daily.

Specific Patient Populations:
- Pediatric patients under 6 years old are dosed based on weight with oral pellets; doses may be adjusted with weight changes.
- Patients with severe renal impairment or on dialysis require close monitoring; the use of Epclusa is possible but should be carefully considered.
- Patients with hepatic impairment:
* Compensated cirrhosis: Standard dosing applies.
* Decompensated cirrhosis: Combination with ribavirin recommended.

Administration Instructions:
- Tablets may be taken orally with or without food.
- Oral pellets: For children unable to swallow tablets; pellets should be swallowed whole without chewing to avoid bitterness. Pellets can be taken alone or mixed in soft food and swallowed within 15 minutes without chewing.
- Pellets must be used immediately after opening the single-use packets.
- Dosing duration for all populations is typically 12 weeks.

Mechanism Of Action

Epclusa combines two direct-acting antiviral agents, sofosbuvir and velpatasvir, that target different viral proteins essential for hepatitis C virus (HCV) replication, providing a complementary antiviral effect.

Sofosbuvir is a nucleotide analogue inhibitor of the HCV NS5B RNA-dependent RNA polymerase, an enzyme critical for viral RNA replication. Once metabolized intracellularly to its active triphosphate form (GS-461203), it competes with natural nucleotides, incorporating into the nascent viral RNA chain and causing chain termination. This effectively halts viral genome replication and diminishes viral load. Sofosbuvir’s mechanism is potent across multiple HCV genotypes owing to the conserved nature of NS5B.

Velpatasvir is an inhibitor of HCV NS5A, a multifunctional nonstructural protein involved in viral RNA replication, virion assembly, and modulation of host cell pathways. NS5A coordinates the replication complex and helps evade host immune responses. By binding to NS5A, velpatasvir disrupts its function, impairing replication complex formation and inhibiting both genome replication and virion assembly. The precise biochemical interaction involves inhibition of NS5A phosphorylation, which is required for its activity.

This dual targeting strategy inhibits two essential viral proteins with non-overlapping mechanisms, minimizing the risk of resistance development and enhancing antiviral efficacy. Clinical studies have demonstrated that this combination achieves sustained virologic response (SVR) rates exceeding 95% across all major HCV genotypes (1 through 6), including in patients with compensated liver disease and those with prior treatment experience.

Compared to similar drugs, such as ledipasvir/sofosbuvir (Harvoni) or glecaprevir/pibrentasvir (Mavyret), Epclusa offers pan-genotypic activity with a simple once-daily dosing regimen. Its favorable safety profile and efficacy in patients with compensated cirrhosis have established it as a cornerstone treatment in HCV infection therapy. Ongoing research supports its use in combination with ribavirin for decompensated cirrhosis and as a salvage regimen after other antiviral failures.

Pharmacological Actions

Inhibition of HCV NS5B RNA-dependent RNA polymerase by sofosbuvir leading to premature termination of viral RNA synthesis.
Inhibition of HCV NS5A protein function by velpatasvir impairing viral replication complex formation and virion assembly.
Pan-genotypic antiviral activity effective against HCV genotypes 1 through 6.
Rapid reduction in HCV viral load resulting in suppression of viral replication.
High barrier to resistance development due to dual targeting of separate viral proteins.
Ability to achieve sustained virologic response (SVR) in chronic hepatitis C patients with and without compensated cirrhosis.
Synergistic antiviral effect when combined with ribavirin in patients with decompensated cirrhosis.
Oral bioavailability enabling convenient once-daily administration.
Minimal impact on host cellular enzymes reducing off-target effects.
Metabolic activation via hepatic intracellular pathways ensuring effective drug targeting.
Combination therapy reduces the duration of HCV treatment to 12 weeks compared to interferon-based regimens.
Significant improvement in liver inflammation and fibrosis through viral eradication.
Demonstrated efficacy in HCV/HIV coinfected patients without dose adjustment.
Effective across diverse patient populations including treatment-naive and treatment-experienced individuals.
Low potential for drug-drug interactions relative to first-generation antivirals.

Therapeutic Or Clinical Uses

Treatment of chronic hepatitis C virus infection in adults and children aged 3 years and older.
Effective against all major HCV genotypes 1 through 6.
Treatment of chronic hepatitis C in patients with and without compensated cirrhosis (Child-Pugh A).
Use in combination with ribavirin for patients with decompensated cirrhosis (Child-Pugh B or C).
Treatment of HCV in patients coinfected with HIV-1 without dose adjustment.
First-line therapy for treatment-naive and treatment-experienced chronic hepatitis C patients.
Pediatric use with oral pellet formulation for children unable to swallow tablets.
Reduction of viral load to undetectable levels, leading to functional cure of hepatitis C.
Prevention of progression of liver disease related to chronic HCV including cirrhosis and hepatocellular carcinoma.
Alternative therapy in patients intolerant or unresponsive to interferon-based regimens.
Facilitates improved liver function and decreases hepatic inflammation post-treatment.
Reduction in the incidence of HCV-related complications such as liver failure and liver transplant requirement.
Used in clinical practice to reduce HCV transmission risk by achieving viral clearance.
Contributes to global efforts in hepatitis C eradication programs.
Provides an effective treatment option with once-daily oral administration improving patient adherence.

Side Or Adverse Effects

Common side effects include headache, which may vary in intensity but is generally mild.
Tiredness and fatigue are frequently reported during treatment courses.
Nausea and occasional vomiting have been observed, requiring supportive care in some cases.
Sleep disturbances such as insomnia may occur, affecting quality of life.
Gastrointestinal symptoms including diarrhea are reported but are usually transient.
Anemia may develop, predominantly in patients with cirrhosis or when combined with ribavirin.
Pale skin and feelings of light-headedness or shortness of breath indicative of anemia or other hematologic effects.
Cold extremities (hands and feet) reflecting peripheral circulatory changes.
Serious hypersensitivity reactions are rare but may include hives, facial swelling, and difficulty breathing.
Elevation of liver enzymes or hepatotoxicity has been reported but is uncommon with Epclusa monotherapy.
Potential reactivation of hepatitis B virus in co-infected patients, necessitating monitoring.
Potential cardiac side effects when coadministered with amiodarone, including arrhythmias and bradycardia.
Rare reports of worsening liver function, especially in patients with advanced hepatic impairment.
Occasional allergic reactions may require immediate medical attention.
Drug-drug interaction related side effects due to altered plasma levels of coadministered drugs.

Precautions

Test for hepatitis B infection before initiation, as reactivation of hepatitis B may occur during or after treatment.
Use caution in patients with decompensated liver disease; combination with ribavirin often necessary.
Careful monitoring advised in patients with renal impairment, especially those on dialysis.
Inform healthcare provider of all comorbid conditions such as diabetes, HIV, or other liver diseases.
Avoid abrupt discontinuation of therapy to prevent viral rebound or resistance.
Patients using blood thinners require close monitoring of INR or prothrombin time during treatment.
Exercise caution when coadministering with amiodarone due to risk of severe bradycardia or cardiac events.
Pregnant women or those planning to become pregnant should avoid concomitant use with ribavirin because of teratogenicity risks.
Breastfeeding safety has not been established; advise consulting healthcare provider before use.
Use effective contraception during treatment and for at least six months post-therapy if ribavirin is coadministered.
Do not share medication to prevent transmission of hepatitis C virus and reduce risk of cross-contamination.
Patients should disclose all concomitant medications including herbal and over-the-counter products to avoid interactions.
Monitor liver function tests regularly during and following treatment, especially in patients with advanced liver disease.
Adjust dosages and monitor closely in pediatric patients, reflecting weight-based dosing considerations.
Instructions for proper administration of oral pellets must be followed to avoid reduced efficacy or taste aversion.

Warnings

May cause reactivation and worsening of hepatitis B infection; monitor patients with previous or current hepatitis B infection carefully.
Avoid use with amiodarone due to risk of severe bradycardia or fatal cardiac events.
Potential risk of birth defects or fetal death if used with ribavirin during pregnancy; contraindicated in pregnant women or partners of males on ribavirin.
Do not modify dosing or stop treatment without consulting a healthcare provider to prevent viral resistance.
Use caution in patients with decompensated cirrhosis; monitor for hepatic decompensation signs including jaundice and ascites.
In patients with impaired renal function, adverse effects may be more pronounced; monitor renal parameters.
Potential interactions with proton pump inhibitors and antacids; omeprazole should not be taken within 4 hours of Epclusa dose.
Patients should avoid unprotected sex or sharing personal items while viremic to prevent HCV transmission.
Use in combination therapy requires careful consideration of additive toxicities and drug-drug interactions.
Report symptoms such as persistent stomach pain, vomiting, loss of appetite, or jaundice immediately.
In rare cases, serious allergic reactions including anaphylaxis have been reported.
Patients with decompensated cirrhosis should be under specialist care when receiving treatment.
Potential for drug-induced liver injury, though rare, necessitates regular clinical and laboratory monitoring.
Caution in elderly patients and those with multiple comorbidities due to limited clinical trial data.
Do not use Epclusa as monotherapy for decompensated cirrhosis; ribavirin coadministration recommended.

Contraindication

Known hypersensitivity or allergic reaction to sofosbuvir, velpatasvir or any component of the formulation.
Concomitant use with amiodarone due to risk of serious cardiac adverse effects.
Pregnancy during ribavirin co-administration due to high risk of fetal harm.
Use in patients with severe hepatic impairment who are not receiving ribavirin is generally contraindicated.
Combination with certain drugs that strongly induce CYP3A4, CYP2B6, or P-glycoprotein which significantly reduce Epclusa efficacy.
Use in patients with hypersensitivity to any inactive ingredients present in tablets or oral pellets.
Use is contraindicated in patients unable to swallow oral capsules or pellets who cannot receive alternative formulations.
Concomitant use with strong inducers of intestinal P-glycoprotein may lead to subtherapeutic drug levels and treatment failure.
Patients with severe renal impairment lacking data on safety and efficacy should be treated cautiously.
Contraindicated in patients using ribavirin who are pregnant or planning pregnancy without effective contraception.
Patients with concurrent uncontrolled hepatitis B without appropriate monitoring or treatment.
Use in combination regimens other than those approved by regulatory authorities is contraindicated.
Contraindicated in combination with other direct-acting antivirals unless clinically justified and supervised.
Use cautiously or avoid in pediatric patients under 3 years of age due to lack of safety data.
Patients with severe cardiovascular conditions should undergo thorough evaluation before initiating treatment.

Drug Interactions

Co-administration with amiodarone can cause serious bradycardia and cardiac conduction abnormalities.
Proton pump inhibitors (e.g., omeprazole) and antacids reduce velpatasvir absorption; avoid simultaneous administration; separate dosing by at least 4 hours.
Strong CYP3A4 and P-glycoprotein inducers such as rifampin, carbamazepine, and St. John's Wort significantly reduce plasma concentrations of sofosbuvir and velpatasvir, leading to decreased efficacy.
Ribavirin should be used cautiously in combination, with monitoring for increased risk of anemia and teratogenicity.
Drugs that affect P-glycoprotein or breast cancer resistance protein (BCRP) transporters may alter drug exposure.
Warfarin and other anticoagulants require close INR monitoring due to possible interaction affecting coagulation parameters.
Concomitant use with HIV protease inhibitors and certain antiretroviral agents may require dose adjustment or monitoring for toxicity.
Co-administration with H2-receptor antagonists should be done at least 12 hours apart to avoid reduced velpatasvir exposure.
Certain antiepileptic drugs (phenytoin, phenobarbital) may reduce Epclusa plasma levels via induction of metabolizing enzymes.
Herbal supplements such as milk thistle and echinacea may interact with drug metabolism pathways affecting efficacy.
Metformin and other diabetes medications may require monitoring for glycemic control while on Epclusa.
Medications affecting hepatic function or liver enzymes may alter metabolism and elimination of Epclusa components.
Caution with statins due to potential additive hepatotoxicity.
Patients on immunosuppressants or chemotherapy should be monitored closely for drug interactions.
Drug interaction potential with oral contraceptives; alternative contraception may be advised.

Preparations Of The Drug

Tablets available in strengths of 400 mg sofosbuvir with 100 mg velpatasvir and 200 mg sofosbuvir with 50 mg velpatasvir.
Oral pellets formulated in single-use packets containing either 150 mg sofosbuvir and 37.5 mg velpatasvir or 200 mg sofosbuvir and 50 mg velpatasvir.
Tablets film-coated with inactive ingredients including copovidone, croscarmellose sodium, magnesium stearate, microcrystalline cellulose, iron oxide red, polyethylene glycol, polyvinyl alcohol, talc, and titanium dioxide.
Oral pellets composed of colloidal silicon dioxide, copovidone, croscarmellose sodium, lactose monohydrate, magnesium stearate, microcrystalline cellulose, and film coating with amino methacrylate copolymer, hypromellose, L-tartaric acid, polyethylene glycol, stearic acid, talc, and titanium dioxide.
Packaged for storage below 30 degrees Celsius (86 ºF) to maintain stability.
Pellets supplied in cartons containing single-dose packets designed to facilitate accurate and hygienic administration in pediatric patients.
Tablets intended for oral use and may be administered with or without food to enhance patient compliance.
Pellets designed for patients unable to swallow tablets; advised to be taken whole or with food without chewing to reduce bitterness.
Packaging includes clear administration instructions to prevent medication errors and preserve drug efficacy.
Epclusa preparations are distributed by Gilead Sciences, Inc., ensuring adherence to regulatory manufacturing standards.
Formulations designed to optimize pharmacokinetic properties and minimize adverse events.
Oral pellets manufactured to enable flexible dosing according to patient's weight and age in pediatric populations.
Both tablets and pellets ensure combination delivery of sofosbuvir and velpatasvir in fixed-dose ratios for consistent therapeutic effect.
Active pharmaceutical ingredients are co-formulated to enhance stability and facilitate once-daily dosing.
Packaging includes medication guides and patient instructions detailing proper use, storage, and safety warnings.