Peginterferon Alfa-2a Injection
Peginterferon alfa-2a injection (Pegasys) is an antiviral medication used to treat chronic hepatitis C and chronic hepatitis B in eligible adults and children.
🧬 Where this information comes from Click to expand
The clinical label records used on this page are FDA-filed Structured Product Labeling (SPL) retrieved through openFDA. We identified 1 clinical label set within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. Forms, routes, brands, labelers, strengths, and NDC product-record counts are built separately from matching FDA National Drug Code Directory records. The linked DailyMed document is a representative official source for verification, not the page’s only clinical source. View the linked label on DailyMed →
⚠️ FDA Boxed Warning — the FDA’s strongest safety alert ▾
Pegasys can cause serious — sometimes life-threatening — problems affecting the mind, immune system, blood vessels, and ability to fight infection. These include severe depression, suicidal thoughts, psychotic episodes, autoimmune disorders (where the immune system attacks the body), reduced blood flow to vital organs, and dangerous infections. These risks apply to all patients taking Pegasys. Your doctor will monitor you closely throughout treatment with regular check-ups and lab tests. If symptoms become severe or keep getting worse — such as deep depression, signs of infection, or unusual bleeding — Pegasys may need to be stopped. In many cases, these problems improve after the medication is discontinued.
📖 Peginterferon Alfa-2a Injection: Patient Information Guide
A plain-language walkthrough of Peginterferon Alfa-2a Injection — what it treats, how it works, how it’s taken, side effects, warnings and interactions. Tap any section to expand it.
🎯What it's used for▾
Peginterferon alfa-2a injection (brand name Pegasys) is an antiviral agent approved for two major conditions:
- Chronic hepatitis C (CHC) in adults: Pegasys is used in combination with other hepatitis C antiviral drugs for adults with compensated liver disease. Pegasys monotherapy is only appropriate when other HCV drugs cannot be tolerated or are contraindicated. It is also approved for adults with CHC co-infected with HIV.
- Chronic hepatitis C in children (age 5–17): Pegasys is used in combination with ribavirin for pediatric patients 5 years and older with compensated liver disease.
- Chronic hepatitis B (CHB) in adults: Pegasys treats both HBeAg-positive and HBeAg-negative CHB in adults with compensated liver disease, evidence of viral replication, and liver inflammation.
- Chronic hepatitis B in children (age 3–17): Pegasys is approved for HBeAg-positive CHB in non-cirrhotic children 3 years of age and older with evidence of viral replication and elevated liver enzymes (ALT).
- Limitations: Pegasys alone or with ribavirin (without additional HCV antiviral drugs) is not recommended for patients who previously failed interferon-alfa therapy, and is not recommended after solid organ transplantation.
⚙️How it works▾
Pegasys works by activating the body's innate antiviral immune response — the built-in system the body uses to recognize and fight viruses. It binds to the human type 1 interferon receptor on cell surfaces, causing those receptors to pair up (dimerize) and trigger a signaling cascade inside the cell. This leads to the production of antiviral proteins that block the hepatitis virus from replicating and spreading further. The "pegylated" part of the drug means it has been chemically attached to a molecule called polyethylene glycol, which slows its clearance from the body and allows once-weekly dosing instead of the more frequent dosing required by older interferon drugs.
💊How it's taken▾
Pegasys is given as a subcutaneous injection (a small shot under the skin) once a week, into the abdomen or thigh. There is no food restriction — it can be taken with or without meals. Treatment duration depends on whether you have hepatitis C or B, the specific virus genotype, your age, and which other drugs are being used alongside Pegasys. Children receive a dose adjusted to their body surface area. If you develop certain side effects — such as low blood counts or significant depression — your doctor may lower the dose or temporarily pause treatment.
- Inject subcutaneously (under the skin) once weekly in the abdomen or thigh
- Duration of treatment varies — follow your prescriber's plan exactly
- Do not adjust your dose or stop treatment without talking to your doctor first
🤒Side effects — in detail▾
Most people experience at least one side effect with Pegasys; the most common ones feel similar to a bad flu, especially early in treatment:
- Fatigue or weakness
- Fever
- Muscle aches
- Headache
- Chills (rigors)
- Nausea or vomiting
- Diarrhea or stomach pain
- Depression, irritability, or trouble sleeping
- Hair thinning (alopecia)
- Injection site reactions
More serious reactions — including severe depression or suicidal thoughts, dangerous drops in blood counts, serious infections, vision changes, heart problems, or severe skin reactions — require prompt medical attention. Contact your doctor right away if any of these develop.
⚠️Warnings & precautions▾
- Serious mental health risks: Pegasys can cause or worsen depression, suicidal thinking, psychosis, aggression, and drug relapse — in patients with or without prior psychiatric history. All patients must be monitored closely throughout treatment.
- Bone marrow suppression: Pegasys lowers white blood cell and platelet counts, increasing infection and bleeding risk. Regular blood tests are required.
- Autoimmune disorders: Pegasys can trigger conditions such as lupus, rheumatoid arthritis, thyroiditis, and inflammatory kidney disease.
- Heart and blood vessel risks: High blood pressure, irregular heart rhythms, chest pain, heart attack, and stroke-like cerebrovascular events have been reported.
- Liver risks: Patients with cirrhosis are at risk of hepatic decompensation (liver failure). Hepatitis B patients may experience temporary but severe hepatitis flares (ALT spikes) during or after treatment.
- Lung complications: Serious lung problems, including pneumonia, pulmonary hypertension, and respiratory failure, can occur.
- Eye problems: Vision loss, retinal damage, and optic nerve inflammation have been reported — a baseline eye exam is required for all patients.
- Growth effects in children: Weight and height gain may slow during treatment in pediatric patients; most children catch up after treatment ends, but long-term data are limited.
- Pregnancy: Pegasys can harm the fetus. When used with ribavirin, both partners must use two effective forms of contraception during treatment and for at least 6 months afterward. Ribavirin is strictly contraindicated in pregnancy.
🔀What it interacts with▾
Pegasys can affect the levels of other drugs in your body and vice versa. Key interactions to know about:
- Theophylline (used for asthma or lung disease): Pegasys inhibits the liver enzyme (CYP1A2) that breaks down theophylline, raising blood levels by about 25% — monitoring and possible dose adjustments are needed.
- Methadone: Pegasys can raise methadone blood levels by 10–15%; watch for signs of toxicity such as extreme drowsiness, slow or shallow breathing, or confusion.
- Zidovudine (an HIV drug, AZT): combining with Pegasys and/or ribavirin significantly increases the risk of severe low white blood cell counts and anemia.
- Other HIV antiretrovirals (NRTIs): patients on certain HIV drugs alongside Pegasys/ribavirin face a higher risk of serious liver decompensation — very close monitoring is required.
- Azathioprine (an immune suppressant): combined use with pegylated interferon and ribavirin has caused severe pancytopenia (dangerous drops in all blood cell types) — this combination should be avoided.
This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.
📋Before taking it▾
- Known allergy to alpha interferons or any component of Pegasys: do not take it — this is a contraindication.
- Autoimmune hepatitis or severe liver failure (hepatic decompensation): Pegasys is contraindicated in these conditions.
- Neonates and infants: Pegasys contains benzyl alcohol and must NOT be used in newborns or infants — it can cause serious and potentially fatal neurological complications.
- Pregnancy: Tell your doctor if you are pregnant or planning to become pregnant. Pegasys can harm a fetus, and when combined with ribavirin, contraception is mandatory for both partners during treatment and for at least 6 months after.
- Breastfeeding: Discuss risks with your doctor; the effects on a nursing infant are not fully known. Mothers co-infected with HIV should not breastfeed.
- History of depression or psychiatric illness: Pegasys can worsen mental health conditions — use with extreme caution and inform your doctor of any history.
- Heart disease: Tell your doctor about any existing heart conditions; Pegasys should be used with caution, especially if you also take ribavirin due to ribavirin-related anemia.
- Kidney disease: Pegasys dose must be reduced in patients with severe kidney impairment (creatinine clearance below 30 mL/min); careful monitoring is needed for any degree of kidney disease.
- Older adults: Side effects involving the nervous system, heart, and flu-like symptoms may be more severe in elderly patients; kidney function should be monitored.
- Diabetes, thyroid disease, or other endocrine conditions: Pegasys can worsen or trigger these — tell your doctor if they are not well-controlled before starting.
🚑If you take too much▾
There is limited experience with Pegasys overdose. The highest recorded dose in any patient was 7 times the intended amount taken daily for 7 days, and no life-threatening reactions were attributed to it directly. Symptoms of too much Pegasys can include severe fatigue, elevated liver enzymes, and dangerously low blood counts (neutropenia and thrombocytopenia). There is no specific antidote, and dialysis does not effectively remove the drug — contact a poison control center or emergency services immediately if overdose is suspected.
📡Pharmacodynamics — effects in the body▾
Pegasys stimulates cells to produce antiviral effector proteins — including serum neopterin and 2',5'-oligoadenylate synthetase — that interfere with the hepatitis virus's ability to replicate inside the body. These proteins are measurable markers that confirm the drug is activating the immune pathway as intended. This immune activation is what drives both the antiviral benefit and many of the side effects (such as fever and fatigue) that patients experience during treatment.
🔬Pharmacokinetics — how your body processes it▾
After a subcutaneous injection, peak blood levels of Pegasys are reached roughly 3 to 4 days (72–96 hours) after the dose. The drug has a very long half-life — averaging about 160 hours (nearly 7 days) — which is why once-weekly dosing works. Steady-state blood levels build up over 5 to 8 weeks of weekly dosing in adults (about 12 weeks in children). Pegasys is cleared much more slowly than older, non-pegylated interferon alfa-2a, which is what makes it more convenient and more consistently active. In patients with severe kidney disease, clearance is reduced and the dose must be lowered; older adults and children also process the drug differently, requiring careful monitoring.
📦How to store it▾
Store in the refrigerator at 2°C to 8°C (36°F to 46°F). refrigerator for more than 24 hours. Do not freeze or shake.
📄 Written from Peginterferon Alfa-2a Injection’s FDA-approved label information, summarized in plain language with AI, and reviewed by our pharmacy team before publication. Every point is grounded in that labeling — nothing is invented. How we use AI →
Supplements & herbs that interact with Peginterferon Alfa-2a Injection
17 supplements and herbal products have documented interactions with Peginterferon Alfa-2a Injection in the licensed clinical database we use. Most are manageable — but your pharmacist should know about everything you take, including vitamins and herbals.
- Major · 1
- Moderate · 7
- Minor · 9
Educational information from a licensed clinical database (Natural Medicines) — see our data sources & update cadence. Not medical advice: an interaction being documented does not mean it will happen to you; do not start or stop medications or supplements without professional guidance.
🩺 Pharmacist Counseling Corner
Quick, plain-English answers to the questions patients ask most about Peginterferon Alfa-2a Injection — the kind of thing our pharmacy team would talk through with you at the counter.
What exactly is Pegasys and why did my doctor prescribe it for hepatitis? ▾
How do I take this medication? Do I have to inject it myself? ▾
The flu-like symptoms are really rough. Is that normal and will they get better? ▾
Should I be worried about depression while I'm on this medication? ▾
Can I use Pegasys if I'm pregnant or trying to get pregnant? ▾
What other medications or health conditions do I need to tell my doctor about before starting? ▾
Is Peginterferon Alfa-2a Injection available over the counter? ▾
When was Peginterferon Alfa-2a Injection first available? ▾
Who makes Peginterferon Alfa-2a Injection? ▾
💬 Answers drafted from Peginterferon Alfa-2a Injection’s FDA-approved label information, summarized in plain language with AI, and reviewed by our pharmacy team before publication. Grounded in that labeling — nothing is made up. How we use AI →
🧰 Keep exploring
💊 How Peginterferon Alfa-2a Injection comes
Peginterferon Alfa-2a Injection is available in 1 form. Different forms and brands can have different approved uses, doses, schedules, and directions. Follow the instructions for your exact product, and do not switch forms without guidance from your prescriber or pharmacist.
Injection
How this form is used
- Pegasys subcutaneous injection is used to treat chronic hepatitis C (CHC) in adults with compensated liver disease, usually in combination with other HCV antiviral drugs
- Pegasys subcutaneous injection is used to treat CHC in children 5 years and older in combination with ribavirin
- Pegasys subcutaneous injection is used to treat chronic hepatitis B (CHB) in adults with compensated liver disease and evidence of active viral replication and liver inflammation
- Pegasys subcutaneous injection is used to treat HBeAg-positive CHB in non-cirrhotic children 3 years of age and older
- Pegasys is injected subcutaneously (just under the skin) once weekly into the abdomen or thigh
- Pegasys dose and treatment duration vary depending on the condition, hepatitis virus genotype, patient age, and whether it is used with other antiviral drugs — always follow your prescriber's instructions
- Pegasys dose may need to be reduced if you develop low blood counts, depression, elevated liver enzymes, or if you have significant kidney impairment — do not adjust the dose on your own
- Pegasys is available as a vial and as a prefilled syringe — follow the administration instructions provided with whichever presentation you are given
📊 Peginterferon Alfa-2a Injection across the U.S. market
How Peginterferon Alfa-2a Injection appears in the FDA’s National Drug Code Directory — including its dosage forms, strengths, brand names, manufacturers, and FDA-listed product records. These are directory records, not sales or prescription volume.
Share of FDA-listed product records by manufacturer — FDA National Drug Code Directory. Record counts are not sales or prescription volume.
📈 How widely Peginterferon Alfa-2a Injection is used
A general measure of how commonly Peginterferon Alfa-2a Injection is prescribed, based on Medicaid — one of the largest public drug programs. The figure below is prescriptions filled in Q1–Q4 2025, summed across every form and brand of the drug.
Think of this as a proxy for how widely Peginterferon Alfa-2a Injection is used, drawn from freely available public data. Medicaid is just one program — these numbers don’t include Medicare, other government coverage, or commercial and cash-pay prescriptions, so real-world use is higher than what’s shown here.
How commonly is Peginterferon Alfa-2a Injection prescribed? Of the 1,596 medications we measure, Peginterferon Alfa-2a Injection ranks #1,377 by Medicaid prescriptions — more than 14% of them.
Utilization by Peginterferon Alfa-2a Injection product
Pick a product to see its own Medicaid numbers. Each chip is one clinical product — a specific strength & dosage form as defined by RxNorm — with brand-name and generic versions combined.
Other Peginterferon Alfa-2a Injection products — combination packs and listings not yet matched to a specific clinical product (kept visible so every prescription is accounted for)
Summed across the 2 of 4 listed NDC products with Medicaid activity.
Shares are of the Medicaid prescriptions shown here. Product grouping follows RxNorm (the National Library of Medicine’s drug terminology), so “one product” means one strength & dosage form regardless of manufacturer. Dollar figures are gross Medicaid reimbursement before mandatory rebates — rebates (often large, especially for brand-name drugs) are confidential, so actual net cost to Medicaid is lower than shown.
Source: Medicaid State Drug Utilization Data (CMS), aggregated by generic ingredient — summed across every NDC (all brands, strengths, salt forms and dosage forms) of Peginterferon Alfa-2a Injection, and across all states and both fee-for-service and managed-care claims. A general popularity signal; it excludes Medicare, commercial insurance and cash prescriptions, so it is not total U.S. use. Based on the 2 of 4 listed Peginterferon Alfa-2a Injection NDCs with Medicaid activity.
🔍 Compare Peginterferon Alfa-2a Injection products
A representative set of FDA-listed product records for Peginterferon Alfa-2a Injection — across manufacturers, strengths, and dosage forms, grouped by form with each product’s manufacturer and how the FDA approved it. The same medicine may be made and packaged by different companies, so a single drug can have many directory entries. (It’s also why a refill can look different — a new shape, color, or box — even though it contains the same medication.)
| Strength | Route | Manufacturer / Labeler | Category ⓘ | Details |
|---|---|---|---|---|
| 💊Injection | ||||
| 180 mcg/0.5 mL | Subcutaneous | Genentech, Inc. × 2 listings | BLA | View NDC → |
| 180 mcg/mL | Subcutaneous | Genentech, Inc. × 2 listings | BLA | View NDC → |
| 180 mcg/0.5 mL | Subcutaneous | pharmaand GmbH × 3 listings | BLA | View NDC → |
| 180 mcg/mL | Subcutaneous | pharmaand GmbH × 3 listings | BLA | View NDC → |
| 180 mcg/0.5 mL | Subcutaneous | zr pharma& GmbH × 2 listings | BLA | View NDC → |
| 180 mcg/mL | Subcutaneous | zr pharma& GmbH × 2 listings | BLA | View NDC → |
Showing 14 of 14 products — FDA National Drug Code Directory. See every product, package size and price: browse all 14 Peginterferon Alfa-2a Injection NDCs →
📈 What people report — real-world data (FDA FAERS)
After a medicine reaches the market, patients, doctors and drugmakers can send the FDA reports of problems they think may be linked to it. Here’s what’s been reported for Peginterferon Alfa-2a Injection — a signal of what to watch for, not proof the drug caused it.
Source: openFDA, from the FDA Adverse Event Reporting System (FAERS). These are voluntary reports — they don’t prove the drug caused the effect, and counts reflect how often something was reported, not how often it actually happens. Reports also often name the very problem the medicine is taken for — a common reason to file one is that the drug didn’t help — so for a pain reliever you may see “pain” high on the list; that points to why the report was filed, not to the drug causing the symptom. This counts every report that lists Peginterferon Alfa-2a Injection in any role, so the total runs higher than the FDA’s official dashboard, which counts only cases where the drug is the suspect. For the authoritative figures, see the FDA FAERS Public Dashboard. Always talk to your pharmacist or doctor.
🏛️ The road to your pharmacy
How Peginterferon Alfa-2a Injection went from FDA review to the pharmacy shelf — the key milestones in its regulatory journey.
Source: Drugs@FDA.
🚨 Recall history
A recall is when a specific batch of a medicine is pulled from the market — usually a manufacturing issue, not a problem with the drug itself. Class I is most serious, Class III least.
Source: openFDA drug enforcement (recall) reports.
RxNorm Concept Web — From Ingredient to Every Form and Strength
This page starts with one ingredient concept (IN). The branches below show its dose-form concepts (SCDF), then the available clinical drug and strength concepts (SCD). Combination products remain separate concepts with their own pages.
RxCUI 120608 3 dose forms · 3 strengths
-
Dose form (SCDF) Injectable Solution RxCUI 378926In current FDA listingsClinical drug / strength (SCD) 0.36 MG/MLRxCUI 403986 -
Dose form (SCDF) Injection RxCUI 1651307In current FDA listingsClinical drug / strength (SCD) 1 ML peginterferon alfa-2a 0.18 MG/MLRxCUI 351270 -
Dose form (SCDF) Prefilled Syringe RxCUI 731325No current FDA listingClinical drug / strength (SCD) 0.5 ML peginterferon alfa-2a 0.36 MG/MLRxCUI 731326
Look up RxCUI 120608 in the RxCUI Atlas →
RxNorm is the U.S. National Library of Medicine’s normalized drug vocabulary. Its concept hierarchy can include forms that are not currently marketed; the status on each branch compares that concept with current FDA listings. RxCUIs identify vocabulary concepts, not individual packages or manufacturers.
📦 Supply & shortage status
Whether Peginterferon Alfa-2a Injection is in short supply in the U.S. right now, plus any shortage history the FDA has on record. A shortage usually reflects a manufacturing or demand issue — not a safety problem with the drug.
Source: openFDA, from the FDA Drug Shortages database.
🏷️ Sold under these brand names
🏭 Manufacturers & labelers
RxNorm drug class
Peginterferon Alfa-2a Injection belongs to the Interferon alpha class.
Classified by RxNorm RxClass — the U.S. National Library of Medicine's standardized drug-classification service (Established Pharmacologic Class from the FDA, the ATC drug family from the WHO, and mechanism of action). Reference only, not medical advice.
🔬 Where this comes from
Core label, product, RxNorm, safety, and utilization data on this page come from the sources identified below. AI-written, editorial, and licensed sections are labeled separately.
How we combine label and product data
HelloPharmacist combines public FDA and NLM records; we don’t author the underlying clinical facts. We identified 1 FDA-filed SPL label set within the page’s selected clinical scope after exact ingredient or ingredient-combination matching and applicable route/form matching. The representative label is the starting point for the displayed reference monograph; the 12 largest stored in-scope SPL records, which may include that representative, are compared section by section, and the longest available version of each section is retained. Forms, routes, brands, labelers, product-listed strengths, and product-record counts are aggregated separately from ingredient-matched FDA NDC Directory records; package records listed above are associated with the linked SPL; and the normalized concept hierarchy comes from NLM RxNorm.
Where a section is identified as AI-written, its plain-language text is generated from bounded label evidence. New draft drug pages remain in the admin review queue before first publication. pharmaand GmbH is the representative DailyMed label linked for verification and dates; it is not the sole source used for the page.
This is general education, not medical advice — always consult your doctor or pharmacist about your medications and any medical condition. For the exact wording of the linked representative label, view that label on DailyMed; some displayed composite sections may come from other in-scope SPL labels. Learn how we use AI and our data sources & update cadence.