In addition to this antihistamine effect, they can have parallel pharmacological properties, for example antimuscarinic and adrenolytic effects which must be considered.It is usual to classify H1-antihistamines into two classes: old ones, called first-generation agents, which are sedating and recent ones, called second-generation agents which have slight or no sedating effects because they do not cross the blood-brain barrier.Antihistamines work by blocking the effects of histamine, a chemical released by mast cells during an allergic response to an allergen.Histamine irritates and inflames the airways to produce sneezing and mucus production.When used over time as an allergy treatment, antihistamines reduce the amount of histamine released by cells and decrease the likelihood that an allergic reaction will occur.Antihistamines are prescribed or recommended for infants, children, and adolescents with allergies and allergic rhinitis.
They are valuable drugs to reduce symptoms due to allergic diseases, especially those mediated by histamine.
It is sometimes used along with Vitamin B6 to stop morning sickness during pregnancy.
Doxylamine is one of the most powerful OTC sedatives in the U. Many patients taking doxylamine encounter dry mouth, nausea, and drowsiness.
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.