There are three subtypes of histamine receptors in vivo: H1, H2, and H3. H1 receptors are mainly distributed in capillaries, bronchi, and intestinal smooth muscle. When H1 receptors are activated, they can cause allergic urticaria, pruritus associated with angioneuroedema, laryngospasm, bronchospasm, and other reactions.H2 receptors are mainly distributed in gastric parietal cells and vascular smooth muscle cells, which can promote gastric acid secretion and capillary expansion.Histamine H1 receptor antagonists are commonly used clinically, such as diphenhydramine, promethazine, chlorphenamine, etc. They are the most widely used nonspecific abnormal antiallergic drugs. They can compete with histamine H1 receptor on the effector cells, so that histamine cannot bind to H1 receptor, thereby inhibiting its role in causing allergic reactions.
Most of these drugs have the following pharmacological effects:
1. Anti peripheral histamine HoneReceptor action
Competes with histamine for H on effector cellsoneReceptor, antagonizing the effect of histamine, can inhibit vascular exudation and reduce tissue edema, which is its main pharmacological effect, and has good effect on some allergic reactions characterized by tissue edema;The inhibitory effect on smooth muscle contraction is far less than that of sympathetic stimulants and theophyllines, and has a certain synergistic effect with adrenaline.
2. Sedative effect
The therapeutic dose of antihistamines can cause central depression such as sedation and lethargy, which may be related to the antagonism of central HoneThe intensity of action varies with individual sensitivity, drug type and dosage.
3. Others
It has the effects of inhibiting secretion, dilating bronchi and relaxing gastrointestinal smooth muscle. Its effects of anti paralysis, preventing vomiting, and preventing dizziness may also be related to its anticholinergic effect.
Scope of application
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1. Allergic disease: mainly applicable to type I allergy (anaphylaxis), with good effect on various allergic skin diseases, such as allergic drug rash and eczema, angioneurotic edema, urticaria, etc;Respiratory allergic diseases, such as allergic rhinitis, pollen rhinitis, etc.
2. It can be used for nausea, vomiting and dizziness caused by motion sickness, radiotherapy and surgery, pregnancy, drugs, Meniere's disease, inflammation of inner ear labyrinth, such as diphenhydramine, dimenhydramine, etc.
3. Promethazine has the most significant antitussive effect.
4. Sedation and hypnosis: it can be used for sedation and hypnosis and for administration before surgery.
5. Anti Parkinson's disease and extrapyramidal symptoms caused by drugs.
Adverse reactions
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The common adverse reactions are sedation, lethargy, fatigue, fatigue, dizziness, headache, dry mouth, blurred vision, constipation, dysuria or urinary retention.A few patients may have mental excitement, insomnia, muscle tremor, arrhythmia, etc.
New antihistamines, such as cetirizine, loratadine, terfenadine, etc., have weak side effects of central inhibition and mild anticholinergic effects.
matters needing attention
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Drivers of vehicles, ships and aircraft, and operators of precision instruments are prohibited from taking antihistamines that inhibit central nervous system before work;Patients with angle closure glaucoma, urinary retention, benign prostatic hyperplasia, pyloric duodenal obstruction, and epilepsy should use caution;Pregnant women and lactating women should use it with caution.The elderly are more sensitive to the adverse reactions of antihistamines, and are prone to hypotension, insanity, dementia, dizziness and other adverse reactions when used.
