What is the recommended approach for allergy treatment that is administered sublingually?

Sublingual Immunotherapy (SLIT): Treatment Approach

Sublingual immunotherapy is an effective, WHO-recognized treatment for allergic rhinitis and rhinoconjunctivitis that involves placing allergen extracts under the tongue, with approximately 80% of randomized controlled trials demonstrating positive results. 1

What SLIT Is and How It Works

SLIT delivers allergen extracts under the tongue to induce immune tolerance through the oral mucosa's tolerogenic environment. 2, 3 The treatment exploits tolerogenic dendritic cells in the sublingual mucosa that promote regulatory T cell differentiation and shift the immune response from allergic Th2 responses toward Th1 responses and IL-10 production. 3

Patient Selection Criteria

Select patients with moderate to severe allergic symptoms who have confirmed IgE sensitization (positive skin test or specific IgE blood test) to the relevant allergen. 1, 4

• SLIT is appropriate for both adults and children, with demonstrated safety even in children under 5 years old 1, 5
• Ideal candidates have inadequate response to optimal pharmacologic treatment with antihistamines and intranasal corticosteroids 1, 6
• Monosensitized patients are ideal, though polysensitized patients can also benefit 1

Critical caveat: Approximately 35% of patients do not show significant benefit in the first year of treatment, so adequate treatment duration extending into a second year may be necessary. 4, 5

Dosing and Administration Protocol

Start directly with the maintenance dose of approximately 5 mg of major allergen per day—no updosing phase is required and does not increase adverse events. 1, 4

Timing and Schedule:

• Begin treatment at least 8 weeks before the pollen season for seasonal allergens 4, 5
• Use a pre-co-seasonal regimen (starting before and continuing through the season) for pollen allergens, as this is supported by the majority of successful trials 1
• Once-daily administration is the standard approach 1
• For optimal efficacy, the maintenance dose should be 15-25 mg of major allergen per day for grass pollen (approximately 30 times the monthly subcutaneous dose), though consensus suggests a minimum of 5 mg per day for other allergens 1

Formulations:

• Sublingual drops (swallowed or spat out) or tablets are available 7
• SLIT requires 20-200 times the dose used in subcutaneous immunotherapy 6, 8

Safety Profile

SLIT demonstrates superior safety compared to subcutaneous immunotherapy, with anaphylaxis being extremely rare (only 3 case reports in the literature) and no SLIT-related fatalities reported. 1, 4, 5

Common Adverse Effects:

• Local oral reactions occur in 0-70% of patients (oral itching, mouth/throat symptoms) but typically remit within 1-2 weeks 1, 4
• Gastrointestinal symptoms may occur but are generally mild 5
• SLIT is safe even at very high doses (up to 500 times the usual monthly subcutaneous dose) 4, 5, 6

Risk Factors:

• Previous systemic reactions to subcutaneous immunotherapy may increase risk 1
• Two anaphylactic events occurred on first doses in patients with prior SCIT systemic reactions 1

Clinical Efficacy

Meta-analysis demonstrates significant reductions in both symptoms (SMD -0.42) and medication requirements (SMD -0.43) compared to placebo. 7

Specific Allergen Evidence:

• Grass pollen, tree pollen, ragweed, dust mite, and parietaria all show efficacy in controlled trials 1, 4, 7
• Ragweed SLIT specifically shows 21% symptom reduction and 29% medication use reduction versus placebo 4
• Dust mite SLIT is effective in both adults and children with allergic rhinitis and asthma 5

Treatment Duration:

• Most positive studies used treatment durations of 6-12 months or longer 1
• Clinical benefits may not be significant until the second year in some cases 4
• Some evidence suggests persistent benefits after therapy conclusion 5

Practical Implementation Pitfalls

Avoid these common errors:

• Do not use homeopathic or low-dose SLIT—it is not supported by evidence 1
• Do not start treatment less than 8 weeks before pollen season 4, 5
• Do not expect complete permanent immunity; sustained benefit does not equal cure 5
• Do not dismiss treatment failure in year one; reassess and continue into year two 4
• Ensure adequate allergen dosing (minimum 5 mg major allergen daily) 1, 4

Guideline Recognition

SLIT has been recognized by the World Health Organization since 1998, the European Academy of Allergy and Clinical Immunology since 1997, and is recommended by the American Academy of Otolaryngology-Head and Neck Surgery for patients with inadequate response to pharmacologic therapy. 1, 6 The ARIA 2010 guidelines provide conditional recommendations with moderate-quality evidence for both adults and children with pollen-induced allergic rhinitis. 6