Management of persistent allergic rhinitis in the tropics: Singapore experiences

Abstract

Allergic rhinitis (AR) is a common manifestation of allergic diseases, affecting 10–25% of the world's population. In the tropics, the majority of AR is persistent. The year-round warm, humid climate is conducive for the proliferation of dust mites and moulds, two of the most common aeroallergens implicated in persistent allergic rhinitis (PAR). The management of AR includes patient education, allergen avoidance, pharmacological treatment, and specific immunotherapy. Patient education, especially regarding dust and mould exposure reduction, can be effective but is often under-utilized. Second generation, non-sedating H₁-antihistamines rapidly relieve most nasal symptoms because they effectively block the histamine H₁-receptors that trigger plasma exudation and oedema. Congestion is most effectively controlled by intranasal glucocorticosteroids (INSs), which are currently the most potent AR drug treatment. The beneficial effects of steroids depend on their long-term, multi-pathway anti-inflammatory effects, unlike H₁-antihistamines, which directly block neural and vascular H₁ receptors. However, especially in PAR, patients' compliance with INS therapy has a significant impact on treatment efficacy, because year-round treatment is required. Subcutaneous inhalant allergen immunotherapy (SCIT) is effective against a broad range of AR symptoms, and may be able to alter the natural course of allergy and prevent asthma onset. SCIT can significantly reduce the severity of allergic disease, including nasal obstruction, and decrease the need for anti-allergic drugs. Immunotherapy (IT) can also be given as sublingual drops (SLIT). Recent studies have shown the SLIT to be effective in reducing AR symptoms and medication use. Both types of IT require long-term patient compliance for successful treatment. Drug and IT interventions may not be economically feasible in certain patients. In conclusion, the type of AR most prevalent in the tropics is PAR, which must be treated year round. Improvement of educational programmes for the public and physicians alike seems to be the most effective treatment strategy.