(There are other types of antihistamines that affect H-2, H-3, and H-4 receptors.) People build up tolerance to them over time and when they stop taking them experience rebound insomnia.Also called histamine antagonists, antihistamines are administered to fight allergic reactions, in which cases sleepiness is considered a possibly undesirable side effect.
That means you can control your symptoms with only 1 or 2 doses each day compared with older medications, which usually require doses every 4 to 6 hours to maintain their effectiveness.
The newer antihistamines are available only by prescription.
A comprehensive review with 185 references for the analysis of commonly prescribed members of an important class of drugs, non-sedating antihistamines (NSAs), is presented.
The review covers most of the methods described for the analysis of cetirizine (CTZ), ebastine (EBS), fexofenadine (FXD), ketotifen (KET) and loratadine (LOR) in pure forms, in different pharmaceutical dosage forms and in biological fluids.
They do, however, have the potential for negative effects if taken with other drugs, so let your doctor know if you are taking more than one medication.