When treating your hives, remember a couple of things. First, it takes an hour or so for the antihistamines to get in your system after you swallow them. Don’t expect them to work in fifteen minutes. Second, you may have to take a larger than recommended dose. Antihistamines are dosed for the nose and the amount of histamine released in a hives outbreak can be much larger than that released in a sneezing attack. If one cetirizine or fexofenadine hasn’t worked in an hour, take a second one. If your hives resolve, you might want to consider continuing a long-acting antihistamines once or twice a day for two weeks to fend off any recurrent bouts.