Antihistamine onset of action: The importance to the patient

Although some older antihistamines have a relatively slow onset of action, modern agents indicate an efficacy between 1 and 3 hours of administration. For patients who use antihistamines regularly, a short onset of action is relatively unimportant. When antihistamines are used as needed, either because of poor compliance or in accordance with emerging therapeutic guidelines, antihistamines with a short onset of action are preferable.