Sofosbuvir

Introduction Overview

Generic Name

sofosbuvir

Brand Name

Sovaldi

Dosage Form

oral tablet and oral pellets

Drug Class

miscellaneous antivirals

Pharmacokinetics

Absorption:
Sofosbuvir is rapidly absorbed following oral administration, reaching peak plasma concentrations within 0.5 to 2 hours. The oral bioavailability of sofosbuvir is high, and its absorption is not significantly affected by food, allowing it to be taken with or without meals. Sofosbuvir oral pellets must be administered without chewing and can be mixed with non-acidic soft foods to facilitate ingestion, especially in pediatric patients. Its rapid absorption ensures achieving effective plasma concentrations necessary for antiviral action.

Distribution:
Once absorbed, sofosbuvir distributes into bodily tissues with an apparent volume of distribution approximating 127 liters. Sofosbuvir is approximately 61-65% bound to plasma proteins, predominantly albumin. It distributes to the liver, the primary site of hepatitis C virus infection. The drug also crosses the placenta but the extent of distribution into breast milk is unknown. Distribution is influenced by factors such as age, hepatic function, and concomitant illness.

Metabolism:
Sofosbuvir is a prodrug that undergoes extensive intracellular metabolism in hepatocytes to its pharmacologically active nucleoside analog triphosphate, GS-461203. The prodrug is initially metabolized by cathepsin A and histidine triad nucleotide-binding protein 1 (HINT1) extracellularly, followed by intracellular conversion. It bypasses the cytochrome P450 system, minimizing significant drug interactions through this pathway. The inactive nucleoside metabolite, GS-331007, is the predominant circulating metabolite found in plasma following sofosbuvir administration.

Elimination:
Sofosbuvir and its metabolites are eliminated primarily by renal excretion. Approximately 80% of the administered dose is recovered in urine, mostly as the inactive metabolite GS-331007; less than 5% is excreted unchanged. The terminal half-life of sofosbuvir is approximately 0.4 hours, while the predominant metabolite GS-331007 has a half-life of 27 hours, supporting once-daily dosing. In patients with renal impairment, especially severe renal dysfunction or dialysis, plasma levels of GS-331007 increase significantly, requiring monitoring. Sofosbuvir's pharmacokinetics are not significantly altered in mild to moderate hepatic impairment.

Dosage Forms

Available Dosage Forms:
- Oral film-coated tablets: 400 mg sofosbuvir per tablet
- Oral pellets: specific doses as determined by weight-based dosing in pediatric patients, to be mixed with non-acidic soft food and swallowed without chewing

Dosages for Adults and Adolescents:
- Adults (≥18 years): 400 mg orally once daily in combination with other antivirals
- Genotype 1 or 4: combined with peginterferon alfa and ribavirin for 12 weeks
- Genotype 2: combined with ribavirin for 12 weeks
- Genotype 3: combined with ribavirin for 24 weeks
- Hepatocellular carcinoma awaiting liver transplantation: combined with ribavirin for up to 48 weeks or until transplantation

Specific Patient Populations:
- Pediatric patients aged 3 years and older:
- Weight < 17 kg: 150 mg orally once daily
- Weight ≥ 17 kg to < 35 kg: 200 mg orally once daily
- Weight ≥ 35 kg: 400 mg orally once daily
Dosing is weight-based, and administration involves use of oral pellets mixed with suitable non-acidic soft foods. Treatment durations mirror those for adults depending on genotype and clinical circumstances.
- Patients with hepatic impairment (Child-Pugh Class A - compensated cirrhosis) can receive standard dosing; safety in more severe hepatic impairment is not well established.
- Patients with renal impairment require careful monitoring, although no dose adjustment is currently recommended for mild to moderate impairment.

Clinical guidelines emphasize that Sovaldi is not to be used as monotherapy; combination therapy with ribavirin and/or peginterferon alfa is essential for effective treatment based on genotype and patient status.

Mechanism Of Action

Sofosbuvir is a nucleotide analog inhibitor of the hepatitis C virus (HCV) NS5B RNA-dependent RNA polymerase, an essential enzyme for viral replication. Upon oral administration, sofosbuvir is metabolized intracellularly to its active triphosphate form, GS-461203, which competes with the natural substrate uridine triphosphate for incorporation into viral RNA.

Incorporation of GS-461203 into the nascent viral RNA chain results in chain termination, thereby halting RNA synthesis and effectively preventing viral genome replication. This selective inhibition blocks HCV's ability to multiply and spread within the host liver cells.

Unlike older treatments, sofosbuvir targets a highly conserved region of the HCV genome, which confers a high barrier to the development of viral resistance. The drug acts at a molecular level without affecting host cellular polymerases, minimizing toxicity.

Clinically, sofosbuvir's mechanism, combined with other antivirals such as ribavirin and peginterferon alfa, achieves a potent antiviral effect that leads to sustained virologic response and potential cure of chronic hepatitis C infection across multiple genotypes. Research and clinical trials have demonstrated that sofosbuvir, through this mechanism, significantly improves treatment outcomes compared to interferon-based regimens alone.

Pharmacological Actions

Direct-acting antiviral agent inhibiting HCV NS5B RNA-dependent RNA polymerase.
Interrupts viral RNA synthesis leading to termination of viral replication.
Acts as a nucleotide analog prodrug with intracellular conversion to active triphosphate.
Selective for viral polymerase, sparing host enzymes to reduce toxicity.
Effective across multiple HCV genotypes, including 1, 2, 3, and 4.
Used in combination antiviral regimens to enhance efficacy and reduce resistance.
Exhibits rapid antiviral activity with sustained virologic response in clinical use.
Demonstrates favorable pharmacokinetics permitting once-daily oral dosing.
Minimal cytochrome P450 metabolism reduces potential for drug interactions.
Has a high genetic barrier to resistance due to targeting conserved viral polymerase domain.

Therapeutic Or Clinical Uses

Treatment of chronic hepatitis C virus (HCV) infection in adults and children aged 3 years and older.
Used in combination regimens with ribavirin and/or peginterferon alfa depending on HCV genotype.
Effective in treating HCV genotypes 1, 2, 3, and 4 with tailored therapy durations.
Treatment option for patients with compensated cirrhosis (Child-Pugh A).
Therapy for HCV/HIV-1 coinfected patients following genotype-specific dosing.
Used for preventing post-liver transplant HCV reinfection in patients awaiting transplantation due to hepatocellular carcinoma.
In combination, enhances sustained virologic response (SVR) rates and potential cure.
Treatment for therapy-naive and therapy-experienced patients who have failed prior interferon-based regimens.
Off-label consideration in some special populations under specialist guidance.
Part of newer direct-acting antiviral regimens improving tolerability compared to interferon-based treatments.

Side Or Adverse Effects

Headache
Fatigue or feeling tired
Nausea
Loss of appetite
Insomnia or sleep disturbances
Anemia, especially when combined with ribavirin
Possible allergic reactions including hives, swelling, or difficulty breathing
Potential worsening or reactivation of hepatitis B infection
Cardiac side effects when co-administered with amiodarone, such as bradycardia and chest pain
Jaundice or signs of liver dysfunction, including dark urine and pale stools
Gastrointestinal discomfort including vomiting or abdominal pain
Rare reports of severe skin reactions and hypersensitivity
Potential worsening of liver function in patients with advanced liver disease
CNS symptoms such as confusion or memory problems, especially with interacting drugs
Risk of birth defects or fetal death when combined with ribavirin during pregnancy

Precautions

Sovaldi must not be used as monotherapy; always in combination with other antiviral agents.
Screen for and monitor hepatitis B infection status prior to and during treatment due to risk of reactivation.
Use caution in patients with renal impairment, especially severe impairment or those on dialysis.
Pregnant women or male patients with pregnant partners must avoid use with ribavirin due to teratogenicity.
Effective contraception with at least two forms of non-hormonal birth control is essential during and 6 months post-treatment when combined with ribavirin.
Monitor liver function tests regularly during and for several months post-treatment.
Be cautious in patients with cardiac conditions if co-administered with amiodarone due to risk of serious bradycardia.
Avoid abrupt discontinuation to prevent viral resistance and treatment failure.
Use with care in patients with previous liver transplantation.
Assess for potential drug-drug interactions with other concurrent medications.
Evaluate patient adherence closely, as irregular dosing can impact treatment success.
Consider potential altered pharmacokinetics in pediatric patients; dosing adjusts by weight.
Potential risk of embryotoxicity necessitates counseling on pregnancy risks.
Limited data on safety and efficacy in patients below 3 years of age; use not approved.
Inform patients about safe practices to prevent HCV transmission during treatment.

Warnings

Risk of hepatitis B virus reactivation, which can worsen liver disease or be fatal.
Do not use Sovaldi as monotherapy; failure to use in combination may lead to viral resistance.
Warning of serious bradycardia events when co-administered with amiodarone; monitor cardiac status.
High teratogenic risk and fetal toxicity when used with ribavirin; contraindicated in pregnancy.
Advise use of effective contraception during treatment and for 6 months afterwards when ribavirin is used.
Patients should be monitored consistently with liver function tests during and after therapy.
Abrupt discontinuation of therapy can make hepatitis C harder to treat and lead to viral rebound.
Not in use for diseases other than HCV; no effect on HIV or AIDS treatment.
No prevention of HCV transmission; patients must observe infection control measures.
Potential drug interactions requiring dose adjustments or close monitoring.
Safety and efficacy not established in patients under 3 years old.
Contains oral pellets which should be used immediately after mixing and not stored.
Serious hypersensitivity reactions may require immediate medical attention.
Frequent monitoring needed for patients on blood thinners due to interaction risks.
Use caution in patients with other liver problems beyond hepatitis C.

Contraindication

Known hypersensitivity to sofosbuvir or any component of the formulation.
Use of sofosbuvir as monotherapy for hepatitis C virus infection.
Pregnancy when used in combination with ribavirin due to teratogenic effects.
Co-administration with amiodarone requires extreme caution due to risk of arrhythmia; generally avoided.
Severe hepatic impairment without established safety data.
Patients younger than 3 years old due to lack of safety and efficacy data.
Concurrent use of certain drugs that have harmful interactions and cannot be safely managed.
Patients who are unwilling or unable to comply with combination therapy regimen.
Known hypersensitivity or allergic reactions to any component of combination regimens including peginterferon alfa or ribavirin.

Drug Interactions

Significant interaction with amiodarone, causing risk of serious bradycardia and cardiac events.
Concomitant use with ribavirin increases risk of anemia and birth defects; requires contraception.
St. John's Wort and other CYP inducers may reduce sofosbuvir plasma concentrations and effectiveness.
Few interactions via cytochrome P450 system due to minimal metabolism by this pathway.
Potential interactions with blood thinners such as warfarin requiring INR monitoring.
Drugs affecting P-glycoprotein (P-gp) can impact sofosbuvir absorption and plasma levels.
Caution with other antiviral agents; dose adjustments may be necessary based on combination.
Herbal supplements may alter sofosbuvir levels; patients should report all supplements.
Antacids and acid-reducing agents have minimal effect, but clinical monitoring advisable.
Rifampin and other strong P-gp inducers can decrease sofosbuvir effectiveness and are not recommended.
Interactions with some immunosuppressants used in transplantation require monitoring.
Close monitoring advised when co-administered with drugs metabolized by similar pathways to assess efficacy and toxicity.
Patients should inform healthcare providers about all current medications to avoid adverse interactions.
No significant interaction with most common drugs due to unique metabolism pathway.
Drug interaction profiles support safe concomitant use with HIV medications under medical supervision.

Preparations Of The Drug

Sovaldi 400 mg oral film-coated tablets for adult use.
Sovaldi oral pellets formulated for pediatric use, administered by mixing with non-acidic soft foods without chewing.
Packaged in blisters or bottles preserving stability under room temperature conditions, away from moisture and heat.
Single-dose packaging to ensure adherence and minimize dosing errors in pediatric populations.
Refrigeration not required; storage at controlled room temperature (20°C to 25°C) recommended.
Available as part of fixed-dose combination therapies with other direct-acting antivirals (e.g., ledipasvir in Harvoni).
Patient medication guides supplied to ensure understanding of dosing, administration, and safety.
Requires prescription and specialized handling instructions for use with ribavirin and peginterferon alfa combinations.
Manufactured following GMP standards to assure consistent quality and potency.
Available in multiple geographic markets with variations in packaging but containing equivalent active ingredient.
Dosage preparations designed to accommodate weight-based pediatric dosing requirements.
Instructional materials provided to support correct mixing and administration of oral pellets.
Associated with comprehensive labeling including warnings, precautions, and drug interaction data.
Distributed through specialty pharmacies and healthcare providers with experience in HCV management.
Preparation forms tailored to optimize compliance and minimize adverse effects in diverse patient populations.