Best treatment would be the one closest to a cure. Three common options for treating allergy are
- Allergen avoidance.
- Drugs to control symptoms (pharmacotherapy).
- AIT (allergy immunotherapy).
1 and 2 are palliative while only 3 comes closest to cure.
HDM (House Dust Mite) Avoidance Is Not Very Effective
Since mites and mite antigens are widely prevalent, complete avoidance isn’t feasible. Avoidance has been the subject of at least threeor other reviews that looked at available data.
- The one for atopic eczema concluded ‘lack of clear evidence‘ in HDM (house dust mite) avoidance/reduction ( ).
- The one for asthma reviewed 54 randomized controlled trials on effect of allergen avoidance (
). Here patients were diagnosed as HDM-sensitive using allergen-specific IgE responses.
- Quality of trials was poor to start with, many of them being non-randomized.
- Meta-analysis after excluding really shoddy trials showed no benefit from HDM avoidance.
- The one for atopic dermatitis reviewed 9 clinical trials for HDM avoidance ( ). Reduction measures included impermeable bedding covers, acaricides, high-efficiency particulate air filters, plus combinations. The only borderline success was with acaricides.
Studies also suggest adherence to avoidance strategies is difficult (, ). Obviously this’ll impact benefit.
Recently, some researchers suggested that Cochrane reviews set too high a bar and exclude too many otherwise worthy studies. In other words, that their reviews suffer from too many false negatives. Given this ambiguity, HDM avoidance is still a widely used approach and will continue to be, at least until better-designed studies provide conclusive evidence either for or against. It’s just that complete HDM avoidance is practically impossible and it’s very difficult to adhere to lifestyle habits necessary for such stringent HDM avoidance.
Pharmacotherapy for HDM allergy Is A Mixed Bag
Unlike for allergens in general, problem with pharmacotherapy for HDM allergy is that many interventions lack sufficient scientific support, in particular few supporting evidence from meta-analysis of randomized controlled trials, i.e., the gold standard. Based on most recent available evidence (see Column 3 in Table below from) then
- Supported by evidence from meta-analysis of randomized controlled trials (gold standard): Inhaled Corticosteroids
- Supported by evidence from at least 1 randomized controlled trial: Oral Antihistamines, Anti-IgE (Omalizumab, etc.), Rapid-acting inhaled \U0001d6c32-agonists, Intranasal Decongestants, Leukotriene modifiers
- Supported by evidence from at least 1 other type of quasi-experimental study: Long-acting inhaled \U0001d6c32-agonists, Intranasal Corticosteroids, Nedocromil sodium
- Supported by evidence from lab based studies: Long-acting inhaled \U0001d6c32-agonists, Systemic Corticosteroids, Theophylline
AIT (Allergy Immunotherapy) Is Close To Prime Time For Allergies In General And For HDM Allergy In Particular
Advantages of AIT are many and include reducing pharmacotherapy dose, frequency, even need. As well, AIT is/can be effective even after Rx is stopped. At least one study on SLIT (Sublingual Immunotherapy) for HDM followed up 3, 4, or 5 years of Rx for 15 years and found 4 years of Rx was optimal duration for long-lasting efficacy (). Two main AIT approaches are SCIT (subcutaneous Immunotherapy) and SLIT.
- Slightly more effective than SLIT.
- Subcutaneous allergen injections done only under doctor’s supervision.
- Best results with sustained Rx for 3 to 5 years.
- Patient compliance is problem since it entails considerable time commitment for several years worth of doctor’s visits.
- Studies suggest SCIT’s quite safe with low rate of systemic reactions, in the range of ~0.2% (7).
- Sublingual allergen tablets or liquid taken conveniently in privacy of one’s home.
- Patient compliance can be problematic because often, patients stop Rx if they develop mild symptoms such as transient tongue swelling or throat itch.
- Best results require sustained Rx for >2 years.
- Studies suggest SLIT is even safer than SCIT with cases of anaphylaxis being extremely rare ( , ).
Calderon et al‘s summary of SCIT and SLIT for allergies in general and for HDM in particular shows (see figures from below)
- For Allergic Rhinitis (AR)
- SLIT is much more effective in general.
- However, SCIT is more effective for AR caused by HDM.
- For Allergic Asthma (AA)
- SCIT more effective in general and for AA caused by HDM.
- Problem is so far too few SLIT studies for AA to know its true effectiveness for this condition.
- As more SLIT studies for HDM are published, this picture will probably likely change.
Current major drawbacks of AIT include
- Ambiguity about allergen extract, batch-to-batch stability, concentration ( , 9, 10). In turn, these affect effective dose.
- Optimal dosing guidelines for SLIT are still insufficient (9, 11) while for SCIT, maintenance dose ranging from 5 to 20µg of major inhaled allergens are found to be effective ( ).
- Most SCIT/SLIT products for HDM contain extracts/protein allergens from the most common dust mites Dermatophgoides pteronyssinus or D. farinae. However, such products may not be optimal in those parts of the world where the dust mite Blomia tropicalis dominates (13). In such places, until commercial products become available, patients may have to depend on made-to-order products. This may increase Rx cost.
- Though several commercial products available for HDM SLIT have demonstrated safety and efficacy, they also show considerable variability in allergen content ( ). These include Allergovac Sublingual Plus from Bial-Aristegui; SLITone ULTRA from ALK-Abello; Staloral 300 Rapid from Stallergenes; Sublivac from Hal Allergy; TOL Forte from Laboratorios Leti. So products with consistent quality is a need of the hour.
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3. Nurmatov, U., et al. “House dust mite avoidance measures for perennial allergic rhinitis: an updated Cochrane systematic review.” Allergy 67.2 (2012): 158-165.
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