Histamine H-3 antagonists

Treatment of allergic rhinitis often involves the use of H-1 antihistamines which block histamine, a primary mediator in allergic responses. Antihista mines alone do not provide significant benefit against the congestion assoc iated with allergic rhinitis and are commonly given in combination with a-a drenergic decongestants. Whereas these decongestants are effective in reduc ing th congestion associated with allergic nasal disease, they may produce undesirable side effects, such as hypertension, agitation and insomnia. Pre sently, we discuss preclinical findings showing that combination histamine H-1 and H-3 receptor blockade produces decongestant activity without the hy pertensive liability characteristic of a-adrenoceptor agonists.