Skip to main content


Generic name: siltuximabsil-TUX-i-mab ]
Drug class: Interleukin inhibitors

Medically reviewed by Philip Thornton, DipPharm. Last updated on Aug 23, 2023.

What is Sylvant?

Sylvant inhibits a certain protein in the body called interleukin-6 (IL-6). High levels of IL-6 can cause an overgrowth of cells in the lymph system (part of your immune system).

Sylvant 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.

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


You should not use Sylvant 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 Sylvant if you are allergic to siltuximab, 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 this medicine. Tell your doctor if you have recently had any signs of infection (fever, chills, body aches).

To make sure Sylvant is safe for you, tell your doctor if you have ever had:

Sylvant may harm an unborn baby. Siltuximab an affect the immune system of a newborn if the mother receives the medicine during pregnancy. Uee 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 Sylvant given?

Sylvant is given as an infusion into a vein, usually once every 3 weeks. A healthcare provider will give you this injection. Follow your doctor's dosing instructions very carefully.

Before each injection, your doctor may perform blood tests to make sure you do not have conditions that would prevent you from safely using Sylvant.

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

Sylvant must be given slowly and the IV infusion can take at least 1 hour to complete.

Siltuximab can lower blood cells that help your body fight infections. Your blood will need to be tested often. Your treatments may be delayed based on the results of these tests.

Dosing information

Usual Adult Dose for Castleman's Disease:

11 mg/kg intravenously over 1 hour every 3 weeks.

Duration of therapy: Until treatment failure.

-Siltuximab was not studied in patients with MCD who are HIV positive or HHV-8 positive because siltuximab did not bind to virally produced IL-6 in a nonclinical study.

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

What happens if I miss a dose?

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

What happens if I overdose?

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

What should I avoid while receiving Sylvant?

Do not receive a "live" vaccine while using Sylvant. 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.

Sylvant side effects

Get emergency medical help if you have any signs of an allergic reaction to Sylvant: 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.

Call your doctor at once if you have:

Common Sylvant side effects may include:

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.

What other drugs will affect Sylvant?

Other drugs may interact with siltuximab, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell each of your health care providers about all medicines you use now 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 Sylvant only for the indication prescribed.

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