Siltuximab is used to treat a certain rare illness (multicentric Castleman's disease - MCD) if you do not have HIV or herpes infections. Siltuximab blocks a certain natural substance that affects the immune system.

Siltuximab can improve the symptoms of MCD including lumps under the skin, fever, weakness or tiredness, or night sweats.

Read the Patient Information Leaflet if available from your pharmacist before you start using siltuximab and each time you get a refill. If you have any questions, ask your doctor or pharmacist.

This medication is given by a health care professional. It is given slowly into a vein as directed by your doctor, usually over 1 hour every 3 weeks. The dosage is based on your weight, medical condition, and response to treatment.

Infusion reactions may happen during the infusion of this drug. Tell your doctor right away if you have any symptoms of infusion reactions such as chest pain/discomfort, pounding heartbeat, wheezing, dizziness, back pain, flushing, nausea, or vomiting. Your doctor may give you other medications to help with these side effects or may slow down or stop your treatment for some time.

Use this medication regularly to get the most benefit from it. To help you remember, use it on the same day every 3 weeks.

Tell your doctor if your condition gets worse.

See also How to Use section.

Dry skin, darkening skin, diarrhea, headache, weight gain, constipation, pain in the arms/legs, or joint pain may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor right away if you have any serious side effects, including:

• easy bleeding/bruising
• signs of infection (such as sore throat that doesn't go away, fever, chills)
• stomach/abdominal pain
• signs of kidney problems (such as change in the amount of urine)

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

• rash
• itching/swelling (especially of the face/tongue/throat)
• severe dizziness
• trouble breathing

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before taking siltuximab, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• active infection
• HIV infection
• a certain herpes infection (human herpes virus-8)
• stomach/intestinal problems (such as ulcers)

Siltuximab can make you more likely to get infections or may make current infections worse. Stay away from anyone who has an infection that may easily spread (such as chickenpox, COVID-19, measles, flu). Talk to your doctor if you have been exposed to an infection or for more details.

This product may cause live bacterial vaccines (such as typhoid vaccine) to not work well. Tell your health care professional that you are using this medication before having any immunizations/vaccinations.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while using siltuximab. Siltuximab may harm an unborn baby. Ask about reliable forms of birth control while using this medication and for 3 months after the last dose. If you become pregnant, talk to your doctor right away about the risks and benefits of this medication.

It is unknown if this medication passes into breast milk. Because of the possible risk to the infant, breastfeeding is not recommended while using this medication and for 3 months after the last dose. Consult your doctor before breastfeeding.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669.

Do not share this medication with others.

Lab and/or medical tests (such as blood counts, platelet counts, uric acid, cholesterol, triglycerides) should be done while you are using this medication. Keep all medical and lab appointments. Consult your doctor for more details.

It is important to get each dose of this medication as scheduled. If you miss a dose, ask your doctor or pharmacist right away for a new dosing schedule. Do not double the dose to catch up.

Not applicable. This medication is given in a hospital or clinic and will not be stored at home.