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IL-1α/β and IL-18 Fusion Protein Trap Pregnancy: Use with caution — IL-1 blockade may affect uterine contraction and parturition; no adequate human data; discuss with maternal-fetal medicine if pregnancy occurs.

Rilonacept (IL-1 Trap — Recurrent Pericarditis)

Brand names: Arcalyst

Adult dose

Dose: Loading: 320 mg SC (two 160 mg injections); Maintenance: 160 mg SC once weekly
Route: Subcutaneous
Frequency: Once weekly (maintenance)
Max: 160 mg/week (maintenance)
Fusion protein containing IL-1RAcP + IL-1R1 extracellular domains — traps IL-1α, IL-1β, and IL-18. Licensed for recurrent pericarditis in adults and adolescents ≥12 years (FDA 2021; MHRA 2022). Targets the inflammasome-driven IL-1β excess underlying idiopathic and recurrent pericarditis. Allows steroid tapering and colchicine reduction.

Paediatric dose

Route: SC
Frequency: Weekly
Max: 160 mg weekly
Licensed for adolescents ≥12 years (weight ≥10 kg): loading 320 mg SC (two 160 mg injections), maintenance 160 mg weekly. Paediatric pharmacokinetics studied in RHAPSODY trial subgroup.

Dose adjustments

Renal

No dose adjustment required.

Hepatic

No dose adjustment required.

Clinical pearls

  • RHAPSODY trial (Klein et al. NEJM 2021): rilonacept vs placebo in recurrent pericarditis — hazard ratio for recurrent pericarditis flare 0.04 (96% reduction; p<0.001); CRP normalisation in 81% vs 13% at 8 weeks. Among the most dramatic results in pericarditis management. FDA approved based on this single pivotal trial
  • IL-1 pathway central to pericarditis: the NLRP3 inflammasome → caspase-1 → IL-1β pathway drives autoinflammatory pericarditis. Colchicine works upstream (NLRP3 inhibition); rilonacept works downstream (IL-1 neutralisation). In refractory cases colchicine-resistant, rilonacept is highly effective because it blocks the final common effector
  • Anakinra as alternative: anakinra (IL-1Ra) at 100 mg SC daily is another IL-1 blocker used for recurrent pericarditis — no UK license for this indication but widely used off-label per ESC 2015 pericarditis guidelines; anakinra has shorter half-life (allows rapid dose adjustment) vs rilonacept (weekly dosing); rilonacept has RCT evidence

Contraindications

  • Active or chronic infections
  • Live vaccines (during and 3 months after — immunosuppression)

Side effects

  • Injection site reactions (very common — erythema, bruising, pain; usually mild and transient)
  • Infections (upper respiratory tract, sinusitis)
  • Dyslipidaemia (cholesterol elevation reported)
  • Neutropenia (rare)

Interactions

  • TNF inhibitors (avoid combination — life-threatening infections reported with IL-1 + TNF blockade)
  • Live vaccines (absolute contraindication)

Monitoring

  • CRP and ESR (inflammatory markers — primary efficacy monitoring)
  • Echocardiogram (effusion size — at baseline and if symptoms recur)
  • Injection site reaction (weekly assessment)
  • CBC (neutropenia)
  • Signs of infection

Reference: BNFc; BNF 90; Klein et al. NEJM 2021 (RHAPSODY trial); MHRA Approval Arcalyst 2022; ESC Pericarditis Guidelines 2015; FDA Prescribing Information Arcalyst 2021. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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