What Is a Topical Antihistamine?

There are three types of histamine receptors in the body: H1, H2, and H3. Among them, H1 receptors are mostly distributed in capillaries, bronchial tubes, and intestinal smooth muscles. When the H1 receptor is activated, it can cause allergic urticaria and angioedema. Itching, laryngospasm, and bronchospasm. H2 receptors are mainly distributed in gastric parietal cells and vascular smooth muscle cells, and can promote gastric acid secretion and capillary dilation. Histamine H1 receptor antagonists, such as diphenhydramine, promethazine, and chlorpheniramine, are commonly used in clinical practice. They are currently the most widely used non-specific abnormal anti-allergic drugs and can compete with histamine for effector cells. The histamine H1 receptor prevents histamine from binding to the H1 receptor, thereby inhibiting its effect of causing allergic reactions.

Basic Information

Chinese name

Antihistamine

Classification

H1 receptor antagonists and H2 receptor antagonists

Attend

Local congestion, edema, increased secretions

Antibody type

H1, H2 and H3 receptors

Antihistamine pharmacological effects

Most of these drugs have the following pharmacological effects:

1. Anti-peripheral histamine H ₁ receptor effect

Competing with H1 receptors on effector cells, antagonizing the effects of histamine, can inhibit vascular exudation and reduce tissue edema. This is its main pharmacological effect, and it is effective for certain allergic reactions characterized by tissue edema. Good; the effect on inhibiting smooth muscle contraction is far inferior to sympathetic stimulants and theophylline, and has a certain synergistic effect with adrenaline.

2. Sedative effect

The therapeutic amount of antihistamines can cause central inhibition such as sedative and lethargic effects, which may be related to antagonizing the central H ₁ receptor. The intensity of the effect varies depending on individual sensitivity, the type and dose of the drug.

3. Other

It has the effects of inhibiting secretion, expanding the bronchi and relaxing the smooth muscles of the gastrointestinal tract. Its anti-tremor paralysis, preventing vomiting, and preventing vertigo may also be related to the anti-cholinergic effect.

Application of antihistamines

1. Allergic diseases: Mainly applicable to type allergies (rapid-type allergic reactions), which has a good effect on various allergic skin diseases, such as allergic drug rash and eczema, angioedema, urticaria, etc. , Such as allergic rhinitis, pollen rhinitis and so on.

2. Can be used for motion sickness, radiotherapy and surgery, pregnancy, drugs, Meniere's disease, nausea caused by labyrinthitis of the inner ear, vomiting, dizziness, such as diphenhydramine, theophylline and so on.

3. Antitussive effect is most significant with promethazine.

4. Sedative hypnosis: can be used for sedative sleeping and pre-operative administration.

5. Anti-Parkinson's disease and drug-induced extrapyramidal symptoms.

Antihistamine adverse reactions

Common adverse reactions are sedation, drowsiness, fatigue, fatigue, dizziness, headache, dry mouth, blurred vision, constipation, difficulty urinating, or retention of urine. A small number of patients may experience mental excitement, insomnia, muscle tremors, and arrhythmias.

New antihistamines, such as cetirizine, loratadine, terfenadine, etc., have less central adverse side effects and less anticholinergic effects.

Antihistamine precautions

Drivers of trains, boats, and aircraft, and operators of precision instruments are prohibited from taking antihistamines with central nervous system suppression before work; angle-closure glaucoma, urinary retention, prostatic hyperplasia, pyloric duodenal obstruction, and epilepsy; use with caution in pregnant women And breastfeeding women with caution. The elderly are more sensitive to adverse reactions to antihistamines, and are prone to adverse reactions such as hypotension, confusion, dementia and dizziness.

(Note: The above content is only for introduction, the drug use must be carried out by a regular hospital under the guidance of a doctor.)