ANTIHISTAMINES - THE OLD AND THE NEW

Several pharmacologic agents provide antihistamine effects by acting a t the H-1 histamine receptor site. The classic agents are relatively n onselective, resulting in a wide range of effects, both therapeutic an d undesirable. The newer agents preferentially block peripheral H-1 re ceptor sites and, consequently, have fewer side effects, including sed ation. Antihistamines are useful in the treatment of allergic conditio ns, Parkinson's disease, insomnia and some forms of nausea, and provid e symptomatic relief of cough and other conditions associated with res piratory tract infections. Certain agents may play a role in the treat ment of asthma and anorexia. Selection of a specific agent should be b ased on cost and the minimization of side effects. The classic antihis tamines provide an inexpensive and highly effective means of treating histamine-mediated symptoms. The bothersome central nervous system sid e effects can be alleviated by taking the drugs at bedtime; their prol onged tissue half-life allows dosing once or twice a day for 24-hour c linical relief. The newer, more expensive nonsedating antihistamines a re acceptable alternatives for patients who are incapable of toleratin g the effects of classic agents.