Siltuximab Injection
Siltuximab Injection is an IL-6 blocker given by intravenous infusion to treat multicentric Castleman's disease (MCD) in people who are HIV negative and HHV-8 negative.
🧬 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 →
Siltuximab (Sylvant) is a specialist IV infusion for multicentric Castleman’s disease in people who are HIV negative and HHV-8 negative. It latches onto IL-6, an immune messenger protein, so IL-6 cannot reach its receptors, and since reaching the U.S. market around 2014 it has generally become the first-line choice for this rare condition. Most people tolerate it well, noticing mainly rash, itching, swelling or weight gain. The thing to watch is infection, because the drug can hide a fever, so call about chills, a cough or feeling unwell rather than waiting for a temperature. Expect blood counts before doses, since low counts can delay an infusion.
Clinical pearls
- During an infusion, tell the nurse right away about back pain, chest discomfort, flushing, nausea or a racing heartbeat.
- Live vaccines are off the table during treatment, and babies exposed in pregnancy may need their live vaccines reviewed too.
- Oral birth control may work less well, so use effective contraception during treatment and for 3 months after stopping.
- If you take warfarin, cyclosporine or theophylline, expect extra monitoring when siltuximab starts or stops, since the effect lingers for weeks.
Patient information guide A plain-language walkthrough of Siltuximab Injection, written from its FDA label.
What Siltuximab Injection is used for
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Siltuximab Injection is used for one condition.
- Sylvant is used for multicentric Castleman's disease (MCD) in people who are HIV negative and HHV-8 negative.
- It was not studied in people with MCD who are HIV positive or HHV-8 positive.
How Siltuximab Injection works
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Siltuximab binds to IL-6, an immune messenger protein. This keeps IL-6 from attaching to its receptors, both free-floating and on cell surfaces.
Too much IL-6 has been linked to body-wide symptoms of MCD. Blocking it helps treat the condition.
Siltuximab Injection dosage
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Sylvant is given by IV infusion only, over about 1 hour, roughly every 3 weeks. It continues until treatment stops working. Food does not apply because it is not taken by mouth.
- Blood counts are checked before each dose for the first 12 months, then every 3 cycles.
- A dose may be delayed if counts are too low, but the dose is not reduced.
- Contact your care team if you miss an appointment.
Dosing details from the FDA-approved label
From the Siltuximab Injection prescribing information (“Dosage and Administration”). Doses are set by your prescriber for your product, condition, kidney function and age — never change a dose on your own.
- Recommended dosage (multicentric Castleman's disease patients receiving SYLVANT)
- 11 mg/kg over 1 hour as an intravenous infusion every 3 weeks until treatment failure
- Perform hematology laboratory tests prior to each dose for the first 12 months and every 3 dosing cycles thereafter. If treatment criteria are not met (before first administration: absolute neutrophil count ≥1.0 × 10 9 /L, platelet count ≥75 × 10 9 /L; retreatment: absolute neutrophil count ≥1.0 × 10 9 /L, platelet count ≥50 × 10 9 /L), consider delaying tre
Read the label’s full dosing text
2 DOSAGE AND ADMINISTRATION For intravenous infusion only. Administer as an 11 mg/kg dose given over 1 hour by intravenous infusion every 3 weeks. ( 2 ) 2.1 Recommended Dosage Administer SYLVANT 11 mg/kg over 1 hour as an intravenous infusion every 3 weeks until treatment failure. Perform hematology laboratory tests prior to each dose of SYLVANT therapy for the first 12 months and every 3 dosing cycles thereafter. If treatment criteria outlined in Table 1 are not met, consider delaying treatment with SYLVANT. Do not reduce dose. Table 1: Treatment Criteria Laboratory parameter Requirements before first SYLVANT administration Retreatment criteria Absolute Neutrophil Count ≥1.0 × 10 9 /L ≥1.0 × 10 9 /L Platelet count ≥75 × 10 9 /L ≥50 × 10 9 /L Hemoglobin SYLVANT may increase hemoglobin levels in MCD patients <17 g/dL <17 g/dL Do not administer SYLVANT to patients with severe infections until the infection resolves. Discontinue SYLVANT in patients with severe infusion related reactions, anaphylaxis, severe allergic reactions, or cytokine release syndromes. Do not reinstitute treatment. 2.2 Instructions for Preparation and Administration Use aseptic technique for reconstitution and preparation of dosing solution. Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit 1. Calculate the dose (mg), total volume (mL) of reconstituted SYLVANT solution required and the number of vials needed. A 21-gauge 1½ inch needle is recommended for preparation. Infusion bags (250 mL) must contain Dextrose 5% in Water and must be made of polyvinyl chloride (PVC), or polyolefin (PO), or polypropylene (PP), or polyethylene (PE). Alternatively PE bottles may be used. 2. Allow the vial(s) of SYLVANT to come to room temperature over approximately 30 minutes. SYLVANT should remain at room temperature for the duration of the preparation. 3. Aseptically reconstitute each SYLVANT vial as instructed in Table 2. Table 2: Reconstitution Instructions Strength Amount of Sterile Water for Injection, USP required for reconstitution Post-reconstitution concentration 100 mg vial 5.2 mL 20 mg/mL 400 mg vial 20 mL 20 mg/mL Gently swirl the reconstituted vials to aid the dissolution of the lyophilized powder. DO NOT SHAKE or SWIRL VIGOROUSLY.
Excerpted — the section continues on the label. Read the full Dosage and Administration section on DailyMed →
Siltuximab Injection side effects
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The most common side effects in studies were:
Common side effects
- Rash
- Itching (pruritus)
- Upper respiratory tract infection
- Weight gain
- High uric acid (hyperuricemia)
- Swelling (edema)
- Nausea, vomiting or diarrhea
- Dizziness
When to get medical help
- Get help right away for signs of a serious allergic reaction (anaphylaxis) during or after an infusion.
- Tell your care team about back pain, chest pain or discomfort, flushing, nausea, vomiting or a racing heartbeat during an infusion.
- Call your doctor about any signs of infection. The drug can hide fever and other signs of inflammation.
- Seek care promptly for symptoms that could suggest a tear in the stomach or bowel wall (GI perforation).
Other common effects included nausea, vomiting, diarrhea, dizziness, high blood pressure and low neutrophil counts. Seek help for signs of allergic reaction, serious infection or possible GI perforation.
Siltuximab Injection warnings and precautions
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- Infections: Do not give during a severe infection. Siltuximab may hide fever and other signs.
- Infusion reactions and anaphylaxis: These are uncommon but can be serious. The infusion is stopped for anaphylaxis, and treatment is discontinued.
- GI perforation: Reported in clinical trials, not in MCD trials. Use caution if you are at higher risk.
- Vaccines: Avoid live vaccines.
Siltuximab Injection interactions
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Siltuximab can change how your body handles some other medicines.
- Warfarin, cyclosporine, theophylline: levels or effect may need monitoring because IL-6 blockade can speed their breakdown.
- Oral contraceptives, lovastatin, atorvastatin: these may work less well.
- Live vaccines: the immune response may be impaired.
- The effect on these enzymes can last several weeks after the last dose.
Interactions listed in the FDA-approved label
From the Siltuximab Injection prescribing information (“Drug Interactions”): what the manufacturer studied or reported to the FDA.
- Cytochrome P450 substrates with a narrow therapeutic index (e.g., warfarin, cyclosporine, theophylline): Inhibition of IL-6 signaling by SYLVANT may restore CYP450 activities to higher levels, leading to increased metabolism of CYP450 substrate drugs compared to metabolism prior to treatment with SYLVANT. Upon initiation or discontinuation of SYLVANT, perform therapeutic monitoring of effect (e.g., warfarin) or drug concentration (e.g., cyclosporine or theophylline) as needed and adjust dose. The effect of SYLVANT on CYP450 enzyme activity can persist for several weeks after stopping therapy.
- CYP3A4 substrate drugs (e.g., oral contraceptives, lovastatin, atorvastatin): Restored CYP450 activity may increase metabolism of CYP3A4 substrates, decreasing their effectiveness. Exercise caution when SYLVANT is co-administered with CYP3A4 substrate drugs where a decrease in effectiveness would be undesirable.
Read the label’s full interactions text
7 DRUG INTERACTIONS 7.1 Cytochrome P450 Substrates Cytochrome P450s in the liver are down regulated by infection and inflammation stimuli including cytokines such as IL-6. Inhibition of IL-6 signaling in patients treated with SYLVANT may restore CYP450 activities to higher levels leading to increased metabolism of drugs that are CYP450 substrates compared to metabolism prior to treatment with SYLVANT. Upon initiation or discontinuation of SYLVANT, in patients being treated with CYP450 substrates with a narrow therapeutic index, perform therapeutic monitoring of effect (e.g., warfarin) or drug concentration (e.g., cyclosporine or theophylline) as needed and adjust dose. The effect of SYLVANT on CYP450 enzyme activity can persist for several weeks after stopping therapy. Exercise caution when SYLVANT is co-administered with CYP3A4 substrate drugs where a decrease in effectiveness would be undesirable (e.g., oral contraceptives, lovastatin, atorvastatin).
Not a complete list. The label covers the interactions the manufacturer studied or reported, and our own interaction database does not cover every medicine either. Bring your full medication list, including vitamins and herbal products, to your pharmacist.
Before taking Siltuximab Injection
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- Do not use after a severe allergic reaction to siltuximab or its ingredients.
- Wait if you have a severe infection.
- Pregnancy: may cause fetal harm. Use effective contraception during treatment and for 3 months after.
- Do not breastfeed during treatment or for 3 months after the last dose.
- Children: safety and effectiveness not established.
- Older adults: similar safety, though greater sensitivity cannot be ruled out.
- Kidney: no starting dose change for CLCr 15 mL/min or higher.
- Liver: no starting change for mild to moderate impairment. Severe impairment was not studied.
What Siltuximab Injection does in the body
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In a study of 30 patients, repeated doses did not cause large changes in the QTc interval (a heart rhythm measurement). IL-6 blood levels should not be used to track the drug's effect, because siltuximab-bound IL-6 interferes with current tests.
How your body processes Siltuximab Injection
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After an IV infusion, blood levels peak near the end of the infusion. Steady state is reached by about the sixth infusion with dosing every 3 weeks. The average half-life is about 20.6 days. Body weight was the only factor that significantly affected clearance, which is why dosing is weight-based. Age and sex did not affect exposure.
How to store Siltuximab Injection
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SYLVANT must be refrigerated at 2°C to 8°C (36°F to 46°F) in the original carton to protect from light. Do not freeze.
Written from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →
Supplements & herbs that interact with Siltuximab Injection
121 supplements and herbal products have documented interactions with Siltuximab 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 · 2
- Moderate · 87
- Minor · 32
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.
Siltuximab Injection: pharmacist answers to common questions
Quick, plain-English answers to the questions patients ask most about Siltuximab Injection — the kind of thing our pharmacy team would talk through with you at the counter.
What is Sylvant for?
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How will I receive it?
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What side effects are common?
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What should I call about right away?
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Can I get vaccines or take my other medicines?
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Is it safe in pregnancy or while breastfeeding?
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Is Siltuximab Injection available over the counter?
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When was Siltuximab Injection first available?
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Answers drafted from the FDA-approved label with AI and reviewed by our pharmacy team. How we use AI →
More about Siltuximab Injection on HelloPharmacist
Siltuximab Injection forms and strengths (how it comes)
Siltuximab 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.
Need a version that does not list lactose, a gluten source, a dye or gelatin? Inactive ingredients differ by manufacturer: see Siltuximab Injection inactive ingredients by manufacturer.
Injection
How this form is used
- Sylvant is used to treat multicentric Castleman's disease in people who are HIV negative and HHV-8 negative.
- Sylvant is for intravenous infusion only.
- Sylvant is given over 1 hour about every 3 weeks.
- Blood counts are checked before Sylvant doses, and a dose may be delayed if counts are too low.
Siltuximab Injection on the U.S. market: products, makers and brands
How Siltuximab 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.
1 company lists 2 Siltuximab Injection product records with the FDA, mostly as injection; the earliest marketing or approval year on record is 2014. Brand names on the directory include Sylvant; the rest are generics.
How widely Siltuximab Injection is used (Medicaid data)
A general measure of how commonly Siltuximab 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 Siltuximab 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 Siltuximab Injection prescribed? Of the 1,601 medications we measure, Siltuximab Injection ranks #1,584 by Medicaid prescriptions — more than 1% of them.
Utilization by Siltuximab 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.
siltuximab 400 MG Injection
Summed across the 1 of 1 listed NDC products with Medicaid activity — every brand and generic of this exact strength & form. RxNorm 1658139
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 Siltuximab 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 1 of 1 listed Siltuximab Injection NDCs with Medicaid activity.
Compare Siltuximab Injection products
A representative set of FDA-listed product records for Siltuximab 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 | ||||
| 100 mg | Intravenous | Recordati Rare Diseases, Inc. | BLA | View NDC → |
| 400 mg | Intravenous | Recordati Rare Diseases, Inc. | BLA | View NDC → |
Showing 2 of 2 products — FDA National Drug Code Directory. See every product, package size and price: browse all 2 Siltuximab Injection NDCs →
Siltuximab Injection side effects reported to the 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 Siltuximab 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 Siltuximab 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.
Siltuximab Injection FDA approval history
How Siltuximab Injection went from FDA review to the pharmacy shelf — the key milestones in its regulatory journey.
Source: Drugs@FDA.
Siltuximab Injection 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.
The FDA’s enforcement reports list no Siltuximab recalls since July 2021.
✅No Siltuximab recalls on record since July 2021Source: FDA enforcement (recall) reports, via openFDA; our copy was last updated Sep 24, 2026.
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 1535218 1 dose form · 2 strengths
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Dose form (SCDF) Injection RxCUI 1658131In current FDA listings
Look up RxCUI 1535218 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.
Siltuximab Injection supply and shortage status
Whether Siltuximab 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.
Siltuximab Injection brand names
Siltuximab Injection is sold under one brand name in the FDA directory — Sylvant. A brand and its generic contain the same active ingredient; the brand name belongs to one company's product.
Who makes Siltuximab Injection: manufacturers and labelers
One company lists Siltuximab Injection products with the FDA. By number of product records, the largest are Recordati Rare Diseases, Inc.. Labelers include manufacturers and repackagers; the product in your bottle depends on which one your pharmacy stocks.
Siltuximab Injection drug class (RxNorm)
Siltuximab Injection belongs to the Interleukin-6 Antagonist 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.
Sources for this Siltuximab Injection page
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 this page is built
HelloPharmacist combines public FDA and NLM records and does not author the underlying clinical facts. The plain-language sections are written with AI from the FDA-approved label text and reviewed by our pharmacy team before publication. EUSA Pharma (UK) Ltd is the representative DailyMed label linked for verification and dates. This is general education, not medical advice: always talk to your doctor or pharmacist about your own medicines. How we build and review drug pages →