The rationale for use of topical corticosteroids in allergic rhinitis.

The rationale for using topical corticosteroids in the treatment of allergic rhinitis is that high drug concentrations can be achieved at receptor sites in the nasal mucosa, with minimal risk of systemic adverse effects. Topical corticosteroids have been demonstrated to reduce the number of Langerhans' cells (or their markers) in the nasal mucosa, and this is thought to attenuate antigen presentation. T lymphocytes have been identified as being significant in orchestrating the immune-inflammatory response, particularly the TH2 cells, which represent an important target for topical corticosteroids. TH2 cell-evoked mast cells and basophils are the sole producers of histamine, a mediator of major importance for rhinitis symptoms. Several studies have shown that the increased number of mast cells and basophils in the epithelium following antigen challenge/exposure, are markedly reduced by topical corticosteroids. Furthermore, the number of eosinophils, an important morphological marker of allergic rhinitis, can be profoundly reduced by treatment with topical corticosteroids. The rationale for topical treatment is strengthened by evidence of inhibition of cytokine release from surface epithelial cells, resulting in reduced recruitment and activation of mast cells, basophils, and eosinophils, which may be attributed to the high drug concentration achieved in epithelial cells. Ongoing inflammation in the mucous membrane is indicated by entry of plasma into the nasal lumen which subsides with the anti-inflammatory efficacy of topical corticosteroids. In contrast to antihistamine therapy, which has little effect on nasal blockage, pretreatment with topical corticosteroids results in almost complete attenuation of late-phase symptoms including nasal blockage, and moderate efficacy in early phase symptoms. Clearly, the spectrum of anti-inflammatory activity afforded by topical corticosteroid therapy is of clinical significance in reducing the three major symptoms of allergic rhinitis- sneezing, watery rhinorrhoea and nasal blockage.