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Dual TYK2/JAK1 Inhibitor (Investigational) Pregnancy: Avoid — insufficient data; JAK inhibitor class signals of fetal harm in animal studies; use contraception.

Brepocitinib (TYK2/JAK1 Inhibitor — Dermatomyositis)

Brand names: PF-06700841 (investigational — regulatory submission 2024)

Adult dose

Dose: 30 mg oral once daily (Phase 3 IMMPACT dose)
Route: Oral
Frequency: Once daily
Max: 30 mg/day
Dual TYK2 and JAK1 inhibitor — targets type I IFN signalling (TYK2) and IFN-γ, IL-6 signalling (JAK1). Phase 3 IMMPACT trial in dermatomyositis (DM) and polymyositis (PM) completed 2023 with positive results. Pfizer regulatory submission to FDA/EMA underway. Could be first FDA-approved treatment specifically for dermatomyositis.

Paediatric dose

Route:
Not yet licensed — regulatory submission pending.

Dose adjustments

Renal

Dose adjustments expected — JAK inhibitors are renally cleared. Specific guidance pending final labelling.

Hepatic

Caution expected in hepatic impairment — pending final labelling.

Clinical pearls

  • IMMPACT trial (Phase 3 — announced 2023): brepocitinib met primary endpoint (Total Improvement Score in myositis at 36 weeks) in dermatomyositis — first Phase 3 positive trial for any targeted therapy in DM/PM. Dermatomyositis has historically been treated with immunosuppressants (azathioprine, IVIG, rituximab) without Phase 3 evidence for any agent
  • Dermatomyositis IFN hypothesis: DM has a strong type I IFN signature in muscle and skin — similar to SLE. TYK2 inhibition targeting IFN-α/β pathway addresses this pathogenic mechanism. IFN signature in muscle biopsy is a marker of disease activity and response in DM — brepocitinib may become the first mechanistically targeted therapy for this condition
  • Anticipated FDA/MHRA submission 2024: if approved, brepocitinib would join anifrolumab (IFN receptor inhibitor) and rilonacept (IL-1) as the third mechanistically novel biologic entering rheumatological practice in a 3-year window — reflecting the explosion of targeted therapies from JAK/TYK2 and cytokine biology

Contraindications

  • Active serious infection
  • Active TB
  • Pregnancy
  • JAK inhibitor contraindications likely to apply (VTE history, malignancy risk — pending label)

Side effects

  • Herpes zoster (TYK2/JAK1 inhibition reduces IFN antiviral defence)
  • Infections (URTI, sinusitis)
  • Laboratory abnormalities (elevated CK from underlying disease normalisation vs drug effect)
  • Potential JAK class risks (VTE, MACE, malignancy — pending long-term safety data)

Interactions

  • Strong CYP3A4 inhibitors (anticipated — similar to other JAK inhibitors)
  • Live vaccines (avoid — immunosuppression)

Monitoring

  • Muscle enzyme levels (CK, LDH, aldolase — myositis activity)
  • IFN signature score (if available — research tool, not yet routine)
  • Muscle strength (MMT8, HAQ-DI)
  • Skin disease (DM rash — heliotrope, Gottron's papules)
  • Pulmonary function (ILD monitoring — common comorbidity in DM)
  • Infection surveillance (particularly herpes zoster)

Reference: BNFc; Pfizer IMMPACT Phase 3 Press Release 2023; Aggarwal et al. ACR 2023 (interim results); Rider et al. Arthritis Rheumatol 2022 (DM treatment review); BNF 90 (not yet licensed). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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