Rilonacept side effects: what 1,120 FDA adverse event reports show
Drug class
Interleukin-1 blocker
Brand names
Arcalyst
Who reports
1,120 reports · 23% serious · 24 with death outcome · 67% female
Used for
ARCALYST (rilonacept) is an interleukin-1 blocker indicated for: Treatment of Cryopyrin-Associated Periodic Syndromes (CAPS), including Familial Cold Autoinflammatory Syndrome (FCAS), and Muckle-Wells Syndrome (MWS) in adults and children 12 years and .
What it is
Rilonacept is a dimeric fusion protein consisting of the ligand-binding domains of the extracellular portions of the human interleukin-1 receptor component (IL-1R1) and IL-1 receptor accessory protein (IL-1RAcP) linked in-line to the Fc portion of human IgG1. Rilonacept has a molecular weight of approximately 251 kDa.
Boxed warning
None in the current label
Causality screen of the 20 strongest signals
What the badges mean
- Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
- Likely indication confounding The term appears in the label's indications: reports probably describe the disease being treated (or its progression), not a drug effect. Classic confounding by indication.
- Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
- Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.
Strongest disproportionality signals
Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 10 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Pericarditis | 84 | 94.8 77.1–116.5ROR 102.3 · χ² 7,666 / p <1e-300 | 92.4 EB05 76.9 · IC025 +5.6 3/3 methods agree | Likely indication confounding term in indications | serious PRR 74.2 | no trial data cached |
| Injection site rash | 65 | 40.1 31.7–50.8ROR 42.6 · χ² 2,440 / p <1e-300 | 39.6 EB05 32.2 · IC025 +4.5 3/3 methods agree | Labeled (related wording) related wording | serious n=5 | no trial data cached |
| Injection site warmth | 27 | 24.6 16.9–35.6ROR 25.1 · χ² 586 / p 7e-130 | 24.2 EB05 17.4 · IC025 +3.5 3/3 methods agree | Labeled (related wording) related wording | serious n=3 | no trial data cached |
| Injection site discomfort | 12 | 21.8 12.4–38.2ROR 22.0 · χ² 217 / p 2e-49 | 20.9 EB05 12.3 · IC025 +2.6 3/3 methods agree | Labeled (related wording) related wording | serious n=2 | no trial data cached |
| Injection site irritation | 14 | 20.7 12.3–34.9ROR 21.0 · χ² 243 / p 4e-55 | 20.0 EB05 12.3 · IC025 +2.7 3/3 methods agree | Not in label — unassessed | serious n=2 | no trial data cached |
| Injection site erythema (redness where injected) | 132 | 20.0 17.1–23.5ROR 22.6 · χ² 2,378 / p <1e-300 | 20.0 EB05 17.3 · IC025 +3.9 3/3 methods agree | Labeled (related wording) related wording | serious PRR 23.4 | no trial data cached |
| Injection site mass | 39 | 19.8 14.6–27.0ROR 20.5 · χ² 678 / p 8e-150 | 19.6 EB05 14.9 · IC025 +3.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 20.4 | no trial data cached |
| Injection site pruritus | 68 | 19.1 15.2–24.1ROR 20.3 · χ² 1,153 / p 5e-253 | 19.0 EB05 15.5 · IC025 +3.7 3/3 methods agree | Labeled (related wording) related wording | serious PRR 20.0 | no trial data cached |
| Injection site reaction | 58 | 15.8 12.3–20.3ROR 16.6 · χ² 793 / p 1e-174 | 15.7 EB05 12.5 · IC025 +3.4 3/3 methods agree | Not in label — unassessed | serious PRR 7.1 | no trial data cached |
| Product complaint | 20 | 15.0 9.7–23.2ROR 15.3 · χ² 248 / p 4e-56 | 14.4 EB05 9.4 · IC025 +2.7 3/3 methods agree | Reporting / coding artifact | serious n=2 | no trial data cached |
| Drug effect less than expected | 11 | 14.6 8.1–26.3ROR 14.7 · χ² 126 / p 1e-29 | 13.1 EB05 6.8 · IC025 +2.2 3/3 methods agree | Reporting / coding artifact | serious n=1 | no trial data cached |
| Injection site urticaria | 18 | 13.9 8.8–22.0ROR 14.1 · χ² 203 / p 3e-46 | 13.1 EB05 8.2 · IC025 +2.6 3/3 methods agree | Labeled (related wording) related wording | serious n=3 | no trial data cached |
| Injection site swelling | 50 | 12.4 9.4–16.2ROR 12.9 · χ² 512 / p 1e-113 | 12.1 EB05 9.4 · IC025 +3.0 3/3 methods agree | Labeled (related wording) related wording | serious PRR 20.1 | no trial data cached |
| Pericardial effusion | 15 | 12.2 7.4–20.2ROR 12.4 · χ² 143 / p 3e-33 | 11.0 EB05 6.5 · IC025 +2.3 3/3 methods agree | Likely indication confounding shares a disease stem with the indications wording | serious PRR 18.7 | no trial data cached |
| Chest pain | 115 | 11.6 9.8–13.8ROR 12.8 · χ² 1,112 / p 4e-244 | 11.5 EB05 9.8 · IC025 +3.2 3/3 methods agree | Not in label — unassessed | serious PRR 5.7 | no trial data cached |
| Injection site haemorrhage | 39 | 9.2 6.8–12.5ROR 9.5 · χ² 278 / p 1e-62 | 8.7 EB05 6.5 · IC025 +2.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 8.8 | no trial data cached |
| Chest discomfort | 50 | 9.2 7.0–12.0ROR 9.6 · χ² 358 / p 5e-80 | 8.8 EB05 6.8 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious PRR 5.5 | no trial data cached |
| Product dose omission issue | 103 | 6.8 5.6–8.1ROR 7.4 · χ² 507 / p 1e-112 | 6.6 EB05 5.6 · IC025 +2.4 3/3 methods agree | Reporting / coding artifact | serious PRR 3.1 | no trial data cached |
| Injection site bruising | 24 | 5.7 3.8–8.5ROR 5.8 · χ² 89 / p 2e-21 | 5.2 EB05 3.7 · IC025 +1.7 3/3 methods agree | Labeled (related wording) related wording | serious PRR 7.2 | no trial data cached |
| Injection site pain (pain where injected) | 87 | 5.4 4.4–6.6ROR 5.7 · χ² 309 / p 2e-69 | 5.2 EB05 4.4 · IC025 +2.0 3/3 methods agree | Labeled (related wording) related wording | serious PRR 8.0 | no trial data cached |
Trial evidence (ClinicalTrials.gov)
Most frequently reported reactions
By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.
| Reaction | Reports | PRR 95% CI · ROR · χ²/p | EBGM EB05 · IC025 | Label screen | Serious-only & strata | Trial cross-check |
|---|---|---|---|---|---|---|
| Injection site erythema (redness where injected) | 132 | 20.0 17.1–23.5ROR 22.6 · χ² 2,378 / p <1e-300 | 20.0 EB05 17.3 · IC025 +3.9 3/3 methods agree | Labeled (related wording) related wording | serious PRR 23.4 | no trial data cached |
| Chest pain | 115 | 11.6 9.8–13.8ROR 12.8 · χ² 1,112 / p 4e-244 | 11.5 EB05 9.8 · IC025 +3.2 3/3 methods agree | Not in label — unassessed | serious PRR 5.7 | no trial data cached |
| Product dose omission issue | 103 | 6.8 5.6–8.1ROR 7.4 · χ² 507 / p 1e-112 | 6.6 EB05 5.6 · IC025 +2.4 3/3 methods agree | Reporting / coding artifact | serious PRR 3.1 | no trial data cached |
| Injection site pain (pain where injected) | 87 | 5.4 4.4–6.6ROR 5.7 · χ² 309 / p 2e-69 | 5.2 EB05 4.4 · IC025 +2.0 3/3 methods agree | Labeled (related wording) related wording | serious PRR 8.0 | no trial data cached |
| Pericarditis | 84 | 94.8 77.1–116.5ROR 102.3 · χ² 7,666 / p <1e-300 | 92.4 EB05 76.9 · IC025 +5.6 3/3 methods agree | Likely indication confounding term in indications | serious PRR 74.2 | no trial data cached |
| Injection site pruritus | 68 | 19.1 15.2–24.1ROR 20.3 · χ² 1,153 / p 5e-253 | 19.0 EB05 15.5 · IC025 +3.7 3/3 methods agree | Labeled (related wording) related wording | serious PRR 20.0 | no trial data cached |
| Injection site rash | 65 | 40.1 31.7–50.8ROR 42.6 · χ² 2,440 / p <1e-300 | 39.6 EB05 32.2 · IC025 +4.5 3/3 methods agree | Labeled (related wording) related wording | serious n=5 | no trial data cached |
| Injection site reaction | 58 | 15.8 12.3–20.3ROR 16.6 · χ² 793 / p 1e-174 | 15.7 EB05 12.5 · IC025 +3.4 3/3 methods agree | Not in label — unassessed | serious PRR 7.1 | no trial data cached |
| Chest discomfort | 50 | 9.2 7.0–12.0ROR 9.6 · χ² 358 / p 5e-80 | 8.8 EB05 6.8 · IC025 +2.6 3/3 methods agree | Not in label — unassessed | serious PRR 5.5 | no trial data cached |
| Injection site swelling | 50 | 12.4 9.4–16.2ROR 12.9 · χ² 512 / p 1e-113 | 12.1 EB05 9.4 · IC025 +3.0 3/3 methods agree | Labeled (related wording) related wording | serious PRR 20.1 | no trial data cached |
| Injection site haemorrhage | 39 | 9.2 6.8–12.5ROR 9.5 · χ² 278 / p 1e-62 | 8.7 EB05 6.5 · IC025 +2.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 8.8 | no trial data cached |
| Injection site mass | 39 | 19.8 14.6–27.0ROR 20.5 · χ² 678 / p 8e-150 | 19.6 EB05 14.9 · IC025 +3.5 3/3 methods agree | Labeled (related wording) related wording | serious PRR 20.4 | no trial data cached |
| Injection site warmth | 27 | 24.6 16.9–35.6ROR 25.1 · χ² 586 / p 7e-130 | 24.2 EB05 17.4 · IC025 +3.5 3/3 methods agree | Labeled (related wording) related wording | serious n=3 | no trial data cached |
| Injection site bruising | 24 | 5.7 3.8–8.5ROR 5.8 · χ² 89 / p 2e-21 | 5.2 EB05 3.7 · IC025 +1.7 3/3 methods agree | Labeled (related wording) related wording | serious PRR 7.2 | no trial data cached |
| Product complaint | 20 | 15.0 9.7–23.2ROR 15.3 · χ² 248 / p 4e-56 | 14.4 EB05 9.4 · IC025 +2.7 3/3 methods agree | Reporting / coding artifact | serious n=2 | no trial data cached |
Unlabeled candidate signals
These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.
- Injection site reaction — n=58, PRR 15.8
- Chest pain — n=115, PRR 11.6
- Chest discomfort — n=50, PRR 9.2
Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.
Common questions
What are the most reported side effects of Rilonacept?
In FDA FAERS, the most frequently co-reported reaction terms for Rilonacept are injection site erythema, chest pain, injection site pain, pericarditis, injection site pruritus, injection site rash. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.
Does Rilonacept have an FDA boxed warning?
No. The FDA label retrieved for Rilonacept has no boxed warning; see the label's Warnings and Precautions for the recognised risks.
Do FAERS signals prove that Rilonacept causes these side effects?
No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.
Sources & methods
- FDA label via openFDA (set ID ad965f38-dd22-4607-a673-2fb92f3b527a, effective 20251216; matched on
openfda.generic_name.exact:"RILONACEPT") - Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
- FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA
count=aggregation, fieldpatient.drug.openfda.generic_name.exact, 30 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction - Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
- Seriousness and sex counts from openFDA
count=serious,patient.patientsex,seriousnessdeath
Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.