Allergic rhinitis: continuous or on demand antihistamine therapy?

Allergic rhinitis is an inflammatory disease of the nasal mucosa, caused by an IgE-mediated reaction after exposure to the allergen to which the patient is sensitized. Histamine is the most important preformed mediator released in the early stage of the allergic reaction, and also contributes to the late phase of the latter, exhibiting proinflammatory effects. Minimal persistent inflammation is a physiopathological phenomenon induced by the presence of an inflammatory cell infiltrate, together with ICAM-1 expression in the epithelial cells of the mucosa exposed to the allergen to which they are sensitized, in the absence of clinical symptoms. This molecule is considered to be an allergic inflammatory marker. The priming effect first described by Connell in 1968 consists of the reduction in the allergen concentration required to elicit a nasal hyper-response when performing a daily nasal exposure test. This implies that with natural exposure to inhaled allergens, small amounts of environmental allergen will maintain the patient symptoms, and thus of course minimal persistent inflammation. Considering the above, it is questionable whether antihistamines should be administered on a continuous basis or upon demand. The antihistamines, and fundamentally the second-generation drugs, have been shown to exert an antiinflammatory effect, and this effect is greater when the drug is administered continuously than when administered upon demand. Likewise, a reduction in treatment cost and an improvement in quality of life among patients treated on a continuous basis has been documented. However, no studies have been specifically designed to clarify the indication of treatment on a continuous basis or upon demand, as occurs in the GINA. As a result, the individualization of treatment according to the concrete characteristics of each patient seems to be the best approach, at least for the time being.