Pharmacology and toxicology of nonclassical antihistamines.

Within the past five years the introduction of a new class of antiallergy drug, the nonsedating antihistamine, has changed the way allergy sufferers are treated. The first example of this new therapeutic class, terfenadine, is a highly specific H1-receptor antagonist devoid of central nervous system activity. In clinical trials to date involving more than 7,000 allergy patients, terfenadine (60 mg twice daily) has been shown to be unsurpassed in efficacy, to have a rapid onset of action, and to have an incidence of sedation not different from that of placebo and considerably less than that of conventional antihistamines. In addition, results of task performance studies, including on-the-road driving studies, have demonstrated a lack of performance impairment with terfenadine at single oral doses of 60 to 240 mg, or with multiple oral doses of 60 mg twice daily for one week. Furthermore, no interaction has been observed between terfenadine and alcohol or diazepam. Postmarketing surveillance of more than 1 billion patient days has substantiated this remarkably safe and effective clinical profile.