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Generic name: siltuximab [ sil-TUX-i-mab ]
Brand name: Sylvant
Dosage form: intravenous powder for injection (100 mg; 400 mg)
Drug class: Interleukin inhibitors

Medically reviewed by on Feb 6, 2023. Written by Cerner Multum.

What is siltuximab?

Siltuximab is used to treat Multicentric Castleman's Disease (MCD). MCD is a rare condition in which the body produces too much of a certain type of white blood cell. MCD can increase your risk of certain cancers by changing the way your immune system works.

Siltuximab is not for use in people who have human immunodeficiency virus (HIV) or human herpesvirus-8.

Siltuximab may also be used for purposes not listed in this medication guide.


You should not use siltuximab if you have a severe infection. Tell your doctor if you have recently had any signs of infection (fever, chills, body aches).

Before taking this medicine

You should not be treated with siltuximab if you are allergic to it, or if you have a severe infection.

If you have a severe illness with fever or any type of infection, you may need to wait until you get better before receiving siltuximab. Tell your doctor if you have recently had any signs of infection (fever, chills, body aches).

Tell your doctor if you have ever had:

  • a chronic infection;

  • a stomach or intestinal disorder, including ulcer or diverticulitis;

  • stomach or intestinal bleeding;

  • gout; or

  • if you have recently received any vaccines, or if you are due to receive one.

Siltuximab may harm an unborn baby. Use effective birth control to prevent pregnancy while you are using this medicine and for at least 3 months after your last dose.

You should not breast-feed while using this medicine.

How is siltuximab given?

Siltuximab is given as an infusion into a vein, usually once every 3 weeks. A healthcare provider will give you this injection.

This medicine must be given slowly, and the infusion can take at least 1 hour to complete.

Siltuximab can increase your risk of bleeding or infection. You will need frequent medical tests. Your siltuximab treatments may be delayed based on the results.

What happens if I miss a dose?

Call your doctor for instructions if you miss an appointment for your siltuximab injection.

What happens if I overdose?

Since siltuximab is given by a healthcare professional in a medical setting, an overdose is unlikely to occur.

What should I avoid while receiving siltuximab?

Do not receive a "live" vaccine while using siltuximab. The vaccine may not work as well and may not fully protect you from disease. Live vaccines include measles, mumps, rubella (MMR), polio, rotavirus, typhoid, yellow fever, varicella (chickenpox), zoster (shingles), and nasal flu (influenza) vaccine.

Siltuximab side effects

Get emergency medical help if you have signs of an allergic reaction: hives; chest tightness, difficult breathing; swelling of your face, lips, tongue, or throat.

Some side effects may occur during the injection. Tell your caregiver right away if you feel nauseated, or have back pain, warmth or redness under your skin, chest pain, pounding heartbeats, fluttering in your chest, or swelling in your face.

Siltuximab may cause serious side effects. Call your doctor at once if you have:

  • bloody or tarry stools, cough with bloody mucus or vomit that looks like coffee grounds;

  • signs of infection, such as fever, chills, painful mouth sores, pain when swallowing, cold or flu symptoms, cough, trouble breathing; or

  • signs of a kidney problem--little or no urination; painful or difficult urination; swelling in your feet or ankles; severe pain in your side or lower back.

Common side effects of siltuximab may include:

  • weight gain;

  • itching or rash;

  • cold symptoms such as stuffy nose, sneezing, sore throat; or

  • high levels of uric acid in your blood (can lead to kidney problems or gout symptoms such as joint stiffness, pain, or swelling).

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Siltuximab dosing information

Usual Adult Dose for Castleman's Disease:

11 mg/kg IV over 1 hour every 3 weeks until treatment failure

Treatment Criteria:
-Requirements before the first dose is given: The absolute neutrophil count (ANC) must be 1 x 10(9) or greater AND the platelet count must be 75 x 10(9) or greater AND hemoglobin must be less than 17 g/dL.
-Retreatment criteria: The absolute neutrophil count (ANC) must be 1 x 10(9) or greater AND the platelet count must be 50 x 10(9) or greater AND hemoglobin must be less than 17 g/dL.

-This drug was not studied in patients with MCD who are HIV positive or HHV-8 positive because it did not bind to virally produced IL-6 in a nonclinical study.
-Perform hematology laboratory tests prior to each dose for the first 12 months and every 3 dosing cycles thereafter.
-Do not initiate therapy in patients with severe infections until the infection resolves.
-Discontinue therapy in patients with severe infusion related reactions, anaphylaxis, severe allergic reactions, or cytokine release syndromes. Do not reinstitute treatment.

Use: For the treatment of patients with multicentric Castleman's disease (MCD) who are human immunodeficiency virus (HIV) negative and human herpesvirus-8 (HHV-8) negative.

What other drugs will affect siltuximab?

Other drugs may affect siltuximab, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.