Antihistamines are substances that suppress the action of free histamine. When the allergen enters the body, histamine is released from the mast cells of the connective tissue that enter the body’s immune system. It begins to interact with specific receptors and cause itching, swelling, rashes and other allergic manifestations. For blocking these receptors, antihistamines respond.
The bulk of antihistamine preparations of the first generation are fat-soluble, can cross the blood-brain barrier and bind to brain H-receptors, which explains the sedative effect of these drugs, which is amplified after taking alcohol or psychotropic drugs. When taking mediotherapeutic doses by children and high toxic adults, psychomotor agitation can occur. Due to the presence of a sedative effect, antihistamines of the 1st generation are not assigned to persons whose activity requires increased attention.
Anticholinergic properties of these drugs cause atropine-like reactions, such as tachycardia, dryness of the nasopharynx and oral cavity, urinary retention, constipation, visual impairment. These features can be beneficial in rhinitis, but can exacerbate airway obstruction caused by bronchial asthma (increases the viscosity of sputum), contribute to exacerbation of prostatic adenoma, glaucoma and other diseases. Simultaneously, these drugs have an antiemetic and anti-sweating effect, reduce the manifestation of parkinsonism.
A number of these antihistamines are included in the combination of drugs that are used for migraines, colds, motion sickness or have a soothing or hypnotic effect.