Antihistamines

Antihistamines are a class of drugs that reversibly block histamine receptors and competitively block histamine binding to receptors, thereby exhibiting antihistamine effects. There are two types of histamine receptors: H1 and H2, and antihistamines are also separated into the corresponding two categories: H1 receptor blockers, such as anti-allergy diphenhydramine; H2 receptor blockers, such as cimetidine which inhibits the secretion of gastric acid.
Antihistamines are widely used in clinical applications, mainly for:
① skin and mucous membrane allergic disease;
② bronchial asthma;
③ motion sickness and vomiting;
④ sedation and hypnosis.
There are no clear guidelines for the safe use of antihistamines in pregnant women. Generally believed, these drugs have no obvious teratogenic effects on the fetus, but the application within 2 weeks before delivery may lead to the formation of posterior fibrous histiocytoma.