What the label lists and what reports show

Siltuximab side effects

Siltuximab's FDA label: “The most common adverse reactions (>10% of patients) were rash, pruritus, upper respiratory tract infection, increased weight, and hyperuricemia.” FAERS holds 631 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is cytokine release syndrome (53 reports).

No generic listed

Check it at the source: the siltuximab FDA label on DailyMed (effective August 27, 2024); the FDA FAERS public dashboard.

What does the patient leaflet say about side effects?

From the patient leaflet: What are the possible side effects of SYLVANT?
SYLVANT may cause serious side effects, including: Infections. SYLVANT may lower your ability to fight infections. Tell your healthcare provider right away if you have any signs or symptoms of an infection during treatment with SYLVANT. Infusion and allergic reactions. If you have an infusion or allergic reaction while receiving SYLVANT, your healthcare provider will stop your infusion and treat your reaction. If you have a severe infusion or allergic reaction, your healthcare provider may stop your treatment completely. […]

Source: FDA drug label, Recordati Rare Diseases, Inc., effective August 27, 2024 (SPL set 8d663642-f52e-49c0-a023-2da083fdfc0b), via openFDA; the full label on DailyMed

What does the label list?

From the label: adverse reactions
The most common adverse reactions (>10% of patients) were rash, pruritus, upper respiratory tract infection, increased weight, and hyperuricemia.

Table 3: Per Patient Incidence of Common Adverse Reactions in Study 1 During Initial 8 Infusions

Reaction	All Grades	Grades 3-4	All Grades	Grades 3-4
Rash (rash, rash generalized, rash maculo-papular, rash popular and rash pruritic)	15 (28%)	1 (2%)	3 (12%)	0
Pruritus	15 (28%)	0	2 (8%)	0
Skin hyperpigmentation	2 (4%)	0	0	0
Eczema	2 (4%)	0	0	0
Psoriasis	2 (4%)	0	0	0
Dry skin	2 (4%)	0	0	0
Lower respiratory tract	4 (8%)	2 (4%)	1 (4%)	1 (4%)
Upper respiratory tract	14 (26%)	1 (2%)	4 (15%)	1 (4%)
Thrombocytopenia	5 (9%)	2 (4%)	1 (4%)	1 (4%)
Edema (general and localized)	14 (26%)	4 (8%)	7 (27%)	0
Constipation	4 (8%)	0	1 (4%)	0
Hypertriglyceridemia	4 (8%)	0	0	0
Hypercholesterolemia	2 (4%)	0	0	0
Hyperuricemia	6 (11%)	1 (2%)	0	0
Oropharyngeal pain	4 (8%)	0	1 (4%)	0
Renal impairment	4 (8%)	0	0	0
Headache	4 (8%)	0	1 (4%)	0
Weight increased	10 (19%)	1 (2%)	0	0
Hypotension	2 (4%)	1 (2%) Anaphylactic reaction	0	0

Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.

From the label: adverse reactions, continued
The following clinically significant adverse reactions are also discussed in other sections of the labeling: Concurrent active severe infections [see Warnings and Precautions (5.1) ] Infusion-related reactions and hypersensitivity [see Warnings and Precautions (5.3) ] Gastrointestinal perforation [see Warnings and Precautions (5.4) ] The most common adverse reactions (>10% of patients) were rash, pruritus, upper respiratory tract infection, increased weight, and hyperuricemia. To report SUSPECTED ADVERSE REACTIONS, contact Recordati Rare Diseases Inc., at 1-888-575-8344 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice. Study 1, in MCD, was an international, multicenter, randomized Phase 2 study of every 3 week infusions comparing SYLVANT and best supportive care (BSC) to placebo and BSC. There were 53 patients randomized to the SYLVANT arm at a dosage of 11 mg/kg and 26 patients randomized to the placebo arm. Of the 26 placebo-treated patients, 13 patients subsequently crossed-over to receive SYLVANT. …

Source: FDA drug label, Recordati Rare Diseases, Inc., effective August 27, 2024 (SPL set 8d663642-f52e-49c0-a023-2da083fdfc0b), via openFDA; the full label on DailyMed

What do FAERS reports show?

631 reports list siltuximab among the medicines taken, each a report of something that happened, not proof the medicine caused it; 128 are coded as a death and 204 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 18 reactions below, 2 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.

Reports received each year

The 25 most reported reactions

Off Label Use (a use or a product term, not a reaction)136
Drug Ineffective (a use or a product term, not a reaction)98
Cytokine Release Syndrome53
Hypertension (named in the label)44
Immune Effector Cell-Associated Neurotoxicity Syndrome42
Disease Progression (a use or a product term, not a reaction)37
Death (an outcome recorded in the report)36
Cataract32
Drug Effective For Unapproved Indication (a use or a product term, not a reaction)32
Hepatic Steatosis31
Cushingoid30
Osteopenia30
Short Stature30
Product Use In Unapproved Indication (a use or a product term, not a reaction)27
Spinal Instability25
Condition Aggravated (a use or a product term, not a reaction)24
Acute Kidney Injury23
Fracture20
Pneumonia20
Fatigue19
Renal Disorder19
Arthropathy18
Growth Retardation18
Pyrexia17
Thrombocytopenia (named in the label)17

Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms

What next?

Siltuximab: the full record: label, generics, price, shortages, recalls
Report a side effect to the FDA: MedWatch
Side effects hub: the most reported medicines and reactions