Antihistamines. Guidelines and implications.

Antihistamines may be used to maximum benefit for the allergic patient if the physician adheres to four guidelines. These guidelines are based upon 1) an appreciation of certain structural and pharmacologic differences among antihistamines, and 2) an understanding of their mechanism of action. Around the clock administration is advisable, the dosage should be titrated for the individual patient, substitutions to another antihistamine should be to a different class of antihistamine, and the efficacy of any single antihistamine usually will diminish with prolonged use, either on the basis of true tolerance or because of psychic factors. There is good theoretical evidence when alpha-adrenergic sympathomimetics, employed as decongestants in combination with antihistamines, should not be given to allergic patients. Two newer drugs, disodium cromoglycate and beclomethasone, may provide symptomatic relief for allergic rhinitis patients. They may benefit the patient who does not obtain full symptomatic relief from antihistamines.