There are two main types of antihistamines: the older group or first –generation sedating antihistamines which can penetrate into the brain and cause drowsiness, and the newer or second – generation non-sedating antihistamines which do not cause tranquil effects on the patients.
Such first-generation antihistamines as brompheniramine (Dimetapp, Bromphen, Dimetane, Nasahist), chlorpheniramine (Chlor-Trimeton), clemastine (Allerhist, Tavist), and diphenhydramine (Benadryl), and a second-generation antihistamine loratadine (Claritin) are non prescription medications.
This means it has an effect on small blood vessels, resulting in dilated capillaries (redness), and leakage of protein-rich fluid into surrounding skin (swelling).
There are at least two kinds of histamine receptors, hence are mainly H1 blockers.
As well as tablets, antihistamines are available as injections, elixirs, and creams.
Antihistamines for Hay Fever (Allergic Rhinitis)Newer oral antihistamines, such as Xyzal (levocetirizine), Zyrtec (cetirizine), Allegra (fexofenadine), Clarinex (desloratadine) and Clarinex (loratadine), are very effective therapies for the treatment of hay fever.