Difference between sedating and non sedating antihistamines
Antihistamines also can be used on an as needed basis for those who experience occasional symptoms or symptoms triggered by exposure to certain irritants such as animal hair, plants, medications, and food products.
Some antihistamines also may be used occasionally to help with sleep.
Almost everyone has taken an antihistamine to treat hay fever, itching, to relieve nausea and vomiting, in tablets and syrups used to treat cough and cold symptoms, or as an aid to sleep.
The popularity of antihistamines is a mute testimony to the diverse negative effects of histamine.
For example, antihistamines are commonly combined with decongestants (for example, Claritin-D, Zyrtec-D, Allegra-D), a class of medicine that is used to dry up the nasal passages and relieve head congestion.
Certain H1 antagonists, such as promethazine, have a local anesthetic effect.
Other H1-antihistamines having an important antimuscarinic activity like diphenhydramine and dimenhydrinate, are used in preventive and curative treatment of motion sickness, but scopolamine which has no antihistamine effect seems more effective than them in preventive treatment.
The drugs of the first antihistamine generation are: promethazine, alimemazine, dexchlorpheniramine, brompheniramine, buclizine, carbinoxamine and doxylamine, are sedating and elicit a drowsiness which can be awkward.
The first-genaration antihistamines have alpha adrenolytic activity which can decrease the vasoconstrictive effect of adrenaline and noradrenaline and an antimuscarinic effect with the corresponding adverse effects.