Abatacept (Orencia): Mechanism, Indications, Dosing, and Safety Profile

Abatacept is a CTLA-4–Ig fusion protein that selectively modulates the CD28/CD80/86 co-stimulation signal required for full T-cell activation, thereby reducing inflammatory cascade in autoimmune arthritis.

FDA Indications

• Rheumatoid arthritis (RA) – moderate to severe, adult; monotherapy or with DMARDs.
• Juvenile idiopathic arthritis (JIA) – polyarticular, age ≥2 years.
• Psoriatic arthritis (PsA) – adult.

Dosing

• Subcutaneous (SC) – 125 mg weekly (weight-based for JIA: 10 kg–<25 kg: 50 mg; 25–<50 kg: 87.5 mg; ≥50 kg: 125 mg).
• IV – 10 mg/kg at weeks 0, 2, 4, then q4w (weight-tiered).

Common Adverse Effects (≥5%)

• Upper respiratory infection, headache, nausea, nasopharyngitis, dizziness.
• Injection-site reactions (SC).

Serious Risks (Boxed Warning)

• Serious infections – TB, invasive fungal, bacterial, viral; screen for latent TB before start.
• Malignancy – Lymphoma, skin cancer reported.
• Hypersensitivity / anaphylaxis.
• COPD exacerbation – Caution in COPD.

Monitoring

CBC, LFTs, infection signs; avoid live vaccines. Cost: ~$5,000–$7,000/month; patient assistance programs available.