Antihistamines in the treatment of asthma

Histamine is an important mediator of asthma. The new anti-histamines which block histamine at the H1-receptor level also possess some anti-allergic properties. At current dosages they appear to be safe. These drugs are effective in the treatment of rhinitis and conjunctivitis but their role in asthma is still under investigation. At a dose higher than usually recommended, they were shown to block exercise-induced asthma and, inconstantly, the early phase reaction after allergen challenge. Their effect on the late phase allergic reaction as well as their clinical efficacy during trials is, however, less consistent. The indication of H1-blockers in the treatment of asthma is therefore limited, especially since doses higher than recommended may lead to adverse reactions.