What are the considerations and recommendations for patients choosing between Sublingual Immunotherapy (SLIT) and Subcutaneous Immunotherapy (SCIT) for allergy treatment?

SLIT vs SCIT for Allergy Treatment

For patients with allergic rhinitis inadequately controlled by pharmacotherapy, both SCIT and SLIT are effective options, but SCIT demonstrates superior efficacy in reducing symptoms and medication use, while SLIT offers a significantly better safety profile with home administration convenience. 1, 2

Efficacy Comparison

SCIT shows greater clinical efficacy than SLIT based on meta-analysis data:

• SCIT achieves a standardized mean difference of -0.92 for symptom scores compared to placebo, significantly higher than SLIT drops (SMD -0.25) and SLIT tablets (SMD -0.40) in grass pollen allergic rhinitis 2
• For medication score reduction, SCIT demonstrates SMD of -0.58 versus SLIT drops SMD -0.37 and SLIT tablets SMD -0.30 2
• Long-term preventive effects (preventing asthma development and new sensitizations) are more convincingly demonstrated for SCIT than SLIT 3, 4

Safety Profile Comparison

SLIT has a substantially superior safety profile:

• Anaphylaxis with SLIT is extremely rare with only 3 case reports in the literature and no SLIT-related fatalities, compared to rare but documented fatal reactions with SCIT 1, 5, 6
• SLIT local reactions (oral itching, mouth/throat symptoms) occur in 0-70% of patients but typically remit within 1-2 weeks 1, 5, 6
• Severe systemic reactions during SCIT are possible but very rare when safety measures are followed 3
• SCIT requires 30-minute post-injection observation in a medical facility capable of treating anaphylaxis 1

Patient Selection Algorithm

Choose SCIT when:

• Maximum efficacy is the priority and patient accepts injection-based therapy 4, 2
• Patient is polysensitized to multiple allergens requiring treatment (SCIT more readily accommodates multiple allergens) 7
• Long-term disease modification and prevention of asthma progression is a primary goal 3, 4
• Patient can commit to regular office visits for injections 1

Choose SLIT when:

• Patient refuses injections or has experienced systemic side effects with SCIT 3, 4
• Home-based administration is strongly preferred for convenience 1, 7
• Safety concerns outweigh the need for maximum efficacy 7, 2
• Patient has seasonal allergic rhinoconjunctivitis to grass, ragweed, or tree pollen with FDA-approved SLIT tablets available 5, 6

Common Eligibility Criteria for Both Modalities

Both SCIT and SLIT require:

• Confirmed IgE sensitization via skin testing or specific IgE blood test to the relevant allergen 1
• At least moderate symptom severity (mild symptoms make detecting treatment differences difficult) 1
• Inadequate symptom control despite optimal pharmacologic treatment with antihistamines and intranasal corticosteroids 1, 6
• Clinician capable of diagnosing and managing anaphylaxis 1

Administration Considerations

SCIT protocol:

• Requires build-up phase with escalating doses administered in physician's office 3
• Maintenance injections typically every 2-4 weeks 3
• Mandatory 30-minute post-injection observation period 1

SLIT protocol:

• Start directly with maintenance dose (approximately 5 mg major allergen daily) without updosing phase 5, 6
• Begin treatment at least 8 weeks before pollen season for seasonal allergens 5, 6
• First dose administered under physician supervision, subsequent doses self-administered at home 3
• Once-daily administration is standard 5

Allergen Selection for Polysensitized Patients

Limit treatment to clinically relevant allergens:

• Polysensitized patients can be treated with a limited number of allergens rather than all positive test results 1
• Select allergens most strongly associated with symptoms based on patient history, timing of symptoms, and exposure patterns 1
• Preferentially choose standardized allergens with documented efficacy in controlled trials 1
• European practice typically uses 1-4 allergens while US practice historically used more allergens, but evidence suggests similar benefits with limited allergen selection 1

Critical Contraindications and Precautions

Absolute contraindications differ between modalities:

• SCIT has stricter contraindications including uncontrolled asthma, severe cardiovascular disease, and beta-blocker use 3
• SLIT contraindications include severe or uncontrolled asthma, active oral inflammation, and recent oral surgery 3
• Previous systemic reaction to SCIT is a risk factor for future reactions and may favor SLIT selection 1

Treatment Duration and Monitoring

Both modalities require extended treatment:

• Minimum 3-year treatment duration recommended for sustained benefit 3
• Clinical benefits may not be significant until the second year of treatment in some cases 5
• Approximately 65% of SLIT trials demonstrate efficacy in the first year, meaning 35% do not show significant initial benefit 5
• Patient adherence is critical for treatment success and is lower than physicians assume for both SCIT and SLIT 3