What are the two classes of antihistamines?

What are the two classes of antihistamines?

Harold Kaiser (Practicing Allergist and Clinical Professor of Medicine, University of Minnesota Medical School) gives expert video advice on: What kind of medications are used to treat allergies?; Does using an EpiPen hurt? and more...

There are generally two classes of antihistamines, the sedating and non-sedating. The sedating antihistamines are the ones that have been around since 1938 or 1940. I think they were first used clinically in 1946. They include the combinations such as benadryl and chlotrimeton and things that we prescribed until about 15 or 20 years ago when another class of non-sedating antihistamines came in. These are therapeutically equivalent, but don't cause the side effects that the first generation anitihistamines, the sedation caused such as the cognitive skill impairment, the drowsiness, and the dry mouth. The sedating antihistamines worked but the price of the side-effects was enormous and people would have to decide whether they really wanted to take this for their allergy. They would feel better but feel hung over or I just don't drive very well with this. The new antihistamines, the nonsedating antihistamines names like Celdane, Clareten, allegra, or zeretech are now available that have the therapeutic effects without the side effects of first generation antihistamines.