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Sylvant Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

Last reviewed on RxList 4/22/2016

Sylvant (siltuximab) is a human-mouse chimeric monoclonal antibody used to treat patients with multicentric Castleman's disease (MCD) who are human immunodeficiency virus (HIV) negative and human herpesvirus-8 (HHV-8) negative. Common side effects of Sylvant include:

  • rash
  • itching
  • upper respiratory tract infection
  • weight gain
  • increased blood level of uric acid
  • swelling
  • constipation
  • mouth and throat pain
  • headache
  • dry skin, and
  • ow blood pressure (hypotension).

The dose of Sylvant is 11 mg/kg given over 1 hour as an intravenous infusion administered every 3 weeks until treatment failure. Sylvant may interact with warfarin, cyclosporine, theophylline, oral contraceptives, lovastatin, and atorvastatin. Tell your doctor all medications and supplements you use. Tell your doctor if you are pregnant or plan to become pregnant before using Sylvant. It is unknown if this drug will harm a fetus. Use birth control during treatment with Sylvant and for 3 months after stopping treatment. It is unknown if this drug passes into breast milk. Breastfeeding while using Sylvant is not recommended.

Our Sylvant (siltuximab) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

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 is Prescribing information?

The FDA package insert formatted in easy-to-find categories for health professionals and clinicians.

Sylvant FDA Prescribing Information: Side Effects
(Adverse Reactions)


The following adverse reactions are also discussed in other sections of the labeling:

  • Concurrent active severe infections [see WARNINGS AND PRECAUTIONS]
  • Infusion-related reactions and hypersensitivity [see WARNINGS AND PRECAUTIONS]

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.

The most common adverse reactions ( > 10% compared to placebo) during treatment with SYLVANT in the MCD clinical trial were pruritus, increased weight, rash, hyperuricemia, and upper respiratory tract infection.

The data presented below in Table 3 were collected from Study 1. 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 dose 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. The median age was 48 years (range 20 to 78), 66% male, 48% Asian, 39% White, 4% Black or African American, 7% other. The patients randomized to SYLVANT received a median of 19 infusions (range 1 to 50) compared to patients randomized to placebo who received a median of 8 infusions (range 2 to 32). To control for disparate exposure between arms, Table 3 reports the per patient incidence of adverse reactions that occurred during the first 8 infusions. Adverse reactions that occurred > 3% in the SYLVANT arm are presented.

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

Placebo + BSC
All Grades Grades 3-4 All Grades Grades 3-4
Skin disorders
  Rash (rash, rash generalized, rash maculo-papular, rash popular and rash pruritic) 15 (28%) 1 (2%) 3 (12%) 0
  Pruritis 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%)
Blood and lymphatic system disorders
  Thrombocytopenia 5 (9%) 2 (4%) 1 (4%) 1 (4%)
General disorders
  Edema(general and localized) 14 (26%) 4 (8%) 7 (27%) 0
Gastrointestinal disorders
  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
Respiratory, thoracic and mediastinal disorders
  Oropharyngeal pain 4 (8%) 0 1 (4%) 0
Renal and urinary disorders
  Renal impairment 4 (8%) 0 0 0
Nervous system disorders
  Headache 4 (8%) 0 1 (4%) 0
  Weight increased 10 (19%) 1 (2%) 0 0
Vascular disorders
  Hypotension 2 (4%) 1 (2%)b 0 0
a Best Supportive Care
b Anaphylactic reaction

SYLVANT was also evaluated as a single agent in another hematologic disease in Study 2. Study 2 was an international, multicenter, randomized Phase 2 study of every 4 week infusions comparing SYLVANT and BSC to placebo and BSC. There were 50 patients randomized to the SYLVANT arm at a dose of 15 mg/kg (unapproved dose) and 26 patients randomized to the placebo arm. The median age was 72 years (range 50 to 85), 58% male, 96% White, 1% Asian, 1% Black, and 1% other. The median number of infusions in both arms was 3 (range 1 to 4). The study was stopped early due to a lack of efficacy. Adverse reactions that occurred > 3% in the SYLVANT arm are presented in Table 4.

Table 4: Per Patient Incidence of Common Adverse Reactions in Study 2

Placebo + BSC
All Grades Grades 3-4 All Grades Grades 3-4
  Lower respiratory tract 4 (8%) 4 (8%) 0 0
General disorders
  Edema (peripheral) 8 (16%) 0 2 (8%) 0
Gastrointestinal disorders
  Abdominal pain/ abdominal distension 6 (12%) 0 0 0
  Decreased appetite 2 (4%) 0 0 0
  Dehydration 2 (4%) 1 (2%) 0 0
Vascular disorders
  Hypotension 3 (6%) 0 0 0

Long Term Exposure

The safety of long term administration of SYLVANT to patients with MCD was evaluated in Study 3. Study 3 enrolled patients from the initial dose finding study of SYLVANT with MCD who were benefiting from chronic SYLVANT therapy. SYLVANT was administered at a dose of 11 mg/kg every 3 to 6 weeks. At the time of data cut off 19 patients were enrolled. The median age was 44 years (range 18 - 76), 63% male, 84% Caucasian, 11% Asian, and 5% Black. The median exposure to SYLVANT for these 19 patients was 5.1 years (range 3.4 to 7.2). The most common adverse reaction ( > 20%) reported by subjects receiving SYLVANT in this study was upper respiratory tract infection (63%); diarrhea (32%); pain in extremities, arthralgia and fatigue (21% each). No patient was removed from therapy for any reason. There were no deaths. There were no cumulative toxicities identified with prolonged treatment with SYLVANT.

Anaphylaxis And Infusion Related Reactions

Approximately 750 patients have been treated with SYLVANT. Of these, one patient experienced an anaphylactic reaction. Data from 249 patients treated with SYLVANT monotherapy forms the basis of the safety evaluation of infusion related reactions. Infusion related reactions were reported in 4.8% of these patients. Symptoms of infusion reactions consisted of back pain, chest pain or discomfort, nausea and vomiting, flushing, erythema, and palpitations.


Immunogenicity data are highly dependent on the sensitivity and specificity of the test methods used. Additionally, the observed incidence of a positive result in a test method may be influenced by several factors, including sample handling, timing of sample collection, drug interference, concomitant medication and the underlying disease. Therefore, comparison of the incidence of antibodies to SYLVANT with the incidence of antibodies to other products may be misleading. The clinical significance of anti-siltuximab antibodies following treatment with SYLVANT is not known.

The immunogenicity of siltuximab has been evaluated using antigen-bridging enzyme immunoassay (EIA) and electrochemiluminescence-based immunoassay (ECLIA) methods. A total of 411 patients across the clinical studies were evaluated at multiple time points for anti-therapeutic antibody (ATA) responses to siltuximab after treatment with SYLVANT. Following SYLVANT dosing, 0.2% (1/411) of patients tested positive for anti-siltuximab antibodies. Further immunogenicity analyses of the single positive sample revealed a low titer of anti-siltuximab antibodies with non-neutralizing capabilities.

No evidence of altered toxicity profile was identified in the patient who developed antibodies to siltuximab.

Read the entire FDA prescribing information for Sylvant (Siltuximab Injection, for Intravenous Infusion)

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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