Subcutaneous Immunotherapy

SCIT Basics - Needle Power Intro

• Subcutaneous Immunotherapy (SCIT): Disease-modifying therapy; repeated administration of gradually increasing doses of specific allergen extracts.
• Goal: Induce clinical tolerance, achieve long-term remission of allergy symptoms.
• Mechanism:
  • Early: Mast cell/basophil desensitization.
  • Late:
    • Shift: ↓Th2 (pro-allergic), ↑Th1 response.
    • Induces: Regulatory T cells (Tregs) → IL-10, TGF-β.
    • Produces: Allergen-specific IgG4 (blocking Abs).
    • Reduces: Allergen-specific IgE over time.
• Key Indications:
  • Allergic Rhinitis/Conjunctivitis (mod-severe, persistent).
  • Allergic Asthma (mild-mod, allergen-driven, controlled).
  • Insect Venom Hypersensitivity (systemic reactions).

⭐ SCIT is the only therapy that alters the natural course of allergic disease, offering potential long-term remission post-discontinuation.

SCIT Regimens - Prickly Protocols

• Phases of SCIT:
  • Build-up Phase: Gradually ↑ doses of allergen extract. Frequency: 1-2 times/week. Duration: 3-6 months.
  • Maintenance Phase: Constant, highest tolerated dose. Frequency: Every 2-4 weeks, then potentially longer intervals. Duration: 3-5 years.
• Conventional Protocol: Most common, gradual dose escalation over months.
• Accelerated Protocols:
  • Cluster: Several injections given on a single day, separated by 20-30 min intervals, weekly/biweekly. Build-up: 4-8 weeks.
  • Rush: Multiple injections over 1-3 days to reach maintenance dose quickly. Higher risk of systemic reactions.
  • Ultra-rush: Maintenance dose reached in 1 day.
• 📌 Mnemonic: "C-C-R-U" (Conventional, Cluster, Rush, Ultra-rush) for protocol types.

⭐ Rush immunotherapy carries a higher risk of systemic allergic reactions compared to conventional protocols, requiring close monitoring in a specialized setting during administration. This is a frequently tested concept regarding patient safety and protocol selection in SCIT for NEET PG.

• Dose adjustments: Based on local/systemic reactions, missed doses, new vial of extract.

SCIT Safety - Reaction Rescue

• Adverse Reactions (ARs):
  • Local ARs: Common; erythema, pruritus, swelling at injection site. Manage: cold compress, oral antihistamines, topical steroids.
  • Systemic ARs (SARs): Less common, potentially life-threatening.
    • Graded by severity (e.g., WAO: Grade 1-Skin/Upper airway; Grade 2-Moderate respiratory/GI; Grade 3-Severe hypoxia/hypotension; Grade 4-Cardiac/Respiratory arrest).
• Anaphylaxis Management: 📌 EpiPen First!
  • STOP SCIT.
  • IM Epinephrine (1:1000): 0.3-0.5 mg (adults); 0.01 mg/kg (max 0.3 mg) (children). Repeat 5-15 min PRN.
  • Supine, elevate legs.
  • Supplemental Oxygen.
  • IV fluids (NS).
  • Antihistamines (H1 & H2 blockers).
  • Corticosteroids (IV/IM).
  • Bronchodilators for bronchospasm.
  • Monitor vitals. Observe 4-6 hrs (biphasic risk).

  ⭐ Epinephrine is cornerstone of anaphylaxis treatment; administer promptly. Delay linked to fatal outcomes.

![EpiPen 2-Pak: Epinephrine Auto-Injector](https://ylbwdadhbcjolwylidja.supabase.co/storage/v1/object/public/notes/L1/ENT_Allergy_and_Immunotherapy_Subcutaneous_Immunotherapy/73f49d9b-26af-4b69-97d9-b2c282ef74b9.cfm)

• Prevention & Precautions:
  • 30-min post-injection observation.
  • Dose adjustment for large local reactions or missed doses.
  • Avoid SCIT during acute illness/fever.

SCIT Outcomes - Allergy Adieu?

• Clinical Efficacy:
  • Significantly ↓ symptoms & medication for allergic rhinitis (AR), allergic asthma, insect venom hypersensitivity.
  • Prevents new allergen sensitizations.
  • Can halt AR progression to asthma, particularly in children.
• Treatment Duration & Long-term Benefit:
  • Typical duration: 3-5 years.
  • Long-lasting remission (years) common post-discontinuation.
  • Relapse possible; retreatment can be effective.
• Key Patient Groups:
  • Children: Highly effective; potential for altering natural disease course.

    ⭐ SCIT is disease-modifying: prevents asthma in AR children & new sensitizations.

  • Pregnancy: Maintenance SCIT generally safe; avoid initiation during pregnancy.
  • Asthmatics: Requires stable, well-controlled asthma (FEV1 > 70% predicted).

High‑Yield Points - ⚡ Biggest Takeaways

• SCIT promotes immune tolerance: shifts Th2 to Th1, boosts Treg cells and IgG4.
• Indicated for allergic rhinitis, asthma, and hymenoptera venom allergy.
• Contraindicated in uncontrolled asthma, with beta-blockers, and active autoimmune disease.
• Involves build-up phase (dose escalation) and maintenance phase (constant dose).
• Treatment duration is typically 3-5 years for sustained benefit.
• Local reactions are common; systemic reactions (e.g., anaphylaxis) are rare but serious.
• Always have epinephrine ready for potential anaphylaxis_._