(1) β-receptor agonist. Beta-agonists have always been rated as the first-choice drug for the treatment of bronchial asthma and play an important role in the treatment. Its main pharmacological effects are as follows: dilate bronchi; increase airway mucociliary clearance; inhibit the release of various inflammatory mediators; inhibit exudative edema; reduce pulmonary hypertension and increase ventricular ejection fraction. Therefore, it can be used to treat bronchial asthma.

Beta-receptor agonists are divided into 3 generations.

①First generation β-receptor agonist. It is characterized by low selectivity and a certain excitatory effect on α, β 1 and β 2 receptors. The action time is short, the application dose is large, and the cardiovascular system side effects are serious. There are mainly some drugs as follows.

Adrenaline: can excite α-receptors and β-receptors, produce an antiasthmatic effect, and reduce congestion and edema of bronchial mucosa. At the same time, it can enhance myocardial contractility, accelerate heart rate, increase cardiac output, increase blood pressure, and increase basal metabolic rate. It has a strong and rapid effect on the bronchus, but it is short-lived and has major side effects, so it is rarely used clinically.

Isoproterenol: has a strong effect on β-receptors. It has almost no effect on α-receptors. Because it is highly excitable to the heart and is prone to drug resistance, it is currently rarely used clinically.

Oxinalin: It has certain selectivity for β2-receptors of bronchial smooth muscle, can significantly relieve bronchial asthma induced by histamine, 5-hydroxytryptamine and acetylcholine, and produce a good bronchodilator effect.

Chlorprenaline: selectively activates β2-receptors, has a significant bronchodilator effect, and has less side effects on the heart. It has a good relieving effect on bronchial asthma induced by histamine and acetylcholine. Clinically suitable for the treatment of bronchial asthma, wheezing bronchitis, etc.

Tritoquinol: Mainly acts on β2-receptors, and also has a papaverine-like effect of directly relaxing bronchial smooth muscle. Its dilation effect on bronchial smooth muscle is 5 to 10 times stronger than that of isoproterenol, and it has less impact on the cardiovascular and central nervous system. There are few adverse reactions, mainly palpitations, heavy head, dry mouth, gastrointestinal reactions, etc.

②Second generation β-receptor agonist. It is characterized by increased selectivity for β2-receptors, enhanced excitatory effects, prolonged action time, and reduced cardiovascular side effects. Commonly used drugs are as follows.

Albuterol: A highly selective and potent beta 2-receptor agonist. It is one of the most widely used antiasthmatic drugs in clinical practice. It has a strong and lasting relaxing effect on bronchial smooth muscle and has little impact on the cardiovascular and central nervous systems. It is considered to be a relatively safe and effective antiasthmatic drug at present. Clinically suitable for bronchial asthma, wheezing bronchitis, bronchospasm, etc. For patients with severe bronchial asthma or status asthmaticus, intravenous drip administration may be considered.

Terbutaline: It highly selectively excites β2-receptors and has a bronchial relaxation effect that is 2 times greater than that of oxinalin. It can also inhibit the release of inflammatory biological mediators, reduce mucosal edema, and increase Mucociliary clearance ability, rarely causes adverse cardiovascular effects when used at recommended doses.

Hexonalin: highly selective stimulant of β2-receptors, less excitable to bronchial smooth muscle, but has extremely weak excitatory effect on the heart and has a long action time. It is suitable for acute and chronic asthma. Reactions include palpitations, finger tremors, headaches, etc.

Others: including bitoterol, reputerol, fenoterol, pirbuterol, etc., all belong to this category of drugs.

③The third generation β-receptor agonist. It is characterized by higher selectivity for β2-receptors and stronger effects. Adverse reactions are reduced and the action time is more than 8 hours. The dosage is generally small, at the microgram level. The main products are as follows.

Clenbuterol: It is a potent and highly selective β2-receptor agonist with obvious bronchodilator effect and little effect on the cardiovascular system. It can be administered orally, atomized and rectally, and is suitable for the treatment of bronchial asthma, asthmatic bronchitis and some types of emphysema that cause bronchospasm. Adverse reactions include temporary dizziness, mild tremor, etc., but they are milder than other varieties.

Procaterol, tuloterol, formoterol and other drugs all fall into this category.

(2) Xanthine drugs.

The pharmacological effects of this class of drugs include: bronchial dilation, achieved by stimulating the release of endogenous catecholamines and inhibiting phosphodiesterase; enhancing the contractility of respiratory muscles; exciting the respiratory center; affecting calcium ion transport; antagonizing the effect of adenylate ; Anti-inflammatory effect. Therefore it can be used for the treatment of asthma. Commonly used drugs are as follows.

① Aminophylline. Oral administration: 0.1 to 0.2 mg, 3 times a day; intravenous administration, the first loading dose is 56 mg/kg body weight, and then maintained at a dose of 0.5 to 0.7 mg/kg body weight.

②Dihydroxypropyltheophylline (dihydroxypropyltheophylline). The medicinal aqueous solution is neutral, has little gastric irritation, is easily absorbed, has a weaker effect than aminophylline, and has fewer cardiovascular side effects, only 1/10 of aminophylline, and is especially suitable for the elderly. 0.1～0.2mg, 3 times a day.

③Chophylline. Similar to dihydroxyprophylline, the side effects are milder than aminophylline, but the effect is also weaker than aminophylline. 0.1～0.2mg, 3 times a day.

④Tripropylxanthine. It is a new type of preparation without adenosine antagonism. It is not metabolized by the liver but is cleared by the kidneys. It avoids large fluctuations in the clearance rate and has no stimulating effect on the central nervous system. It is a promising drug.

(3) Anticholinergic drugs. Anticholinergic drugs exert competitive antagonism by competing with acetylcholine for the same binding site on the M receptor, thereby reducing bronchial tension and relieving the airway obstruction symptoms of bronchial asthma. A large number of clinical studies have shown that aerosolized anticholinergics in stable asthma exert a significant bronchodilator effect. However, compared with selective β-receptor agonists, their relative efficacy is currently highly controversial. Studies on the efficacy of combining anticholinergics with beta-agonists in the treatment of stable asthma show that the vast majority of results show that the efficacy of the combination is not only stronger than either alone, but also lasts significantly longer. These two types of drugs exert airway relaxation through different mechanisms, so their efficacy is independent of each other, and they produce additive effects when used together.

(4) Glucocorticoids. The pharmacological effects of glucocorticoids include: anti-inflammatory effect; anti-allergic effect; relaxing airway smooth muscle; preventing delayed allergic reactions and reducing bronchial hyperresponsiveness. Therefore, corticosteroids can be used to prevent and treat bronchial asthma. Prednisolone and prednisone are often taken orally, 30 mg per day for adults. Maximum effect occurs after a few days, and the dose is reduced to 5 to 15 mg. The usual course of treatment is 7 days. Hydrocortisone can be injected. The first dose is 4 mg/kg body weight, once every 6 hours. It is usually used for 1 to 3 days. When it is effective, it can be taken orally. Aerosol inhalation includes chlortisone dipropionate, budesonide, etc., and the dose is ≤ 800 μg per day.

(5) Anti-allergic drugs. Drugs that interfere with or block every link of airway allergic disease can be called anti-allergic drugs, and these drugs are the first-line drugs for the prevention and treatment of asthma. Commonly used drugs are as follows.

① Sodium cromoglycate. It is a mast cell stabilizer that can inhibit the release of inflammatory mediators from mast cells, inhibit the activation of eosinophils, neutrophils and alveolar macrophages, and has an inflammatory effect against airway allergies. Lung function can be significantly improved with long-term treatment. This medicine is the safest medicine for treating asthma and has very few side effects.

② Ketotifen. The pharmacological effects of ketotifen: inhibit the synthesis and release of inflammatory mediators; antagonize inflammatory mediators; increase the activity of β-receptors and convert them to a high-affinity state; inhibit the release of intracellular Ca2+. The clinical application efficiency can be as high as 90%, with few side effects and only mild sedation after long-term use.

③Antihistamines. This class of drugs can antagonize inflammatory mediators such as histamine, leukotrienes, platelet activating factors and prostaglandins, and can also inhibit the release of mediators by inflammatory cells such as mast cells, eosinophils, basophils and alveolar macrophages. Commonly used drugs include: azelastine, terfenadine, cetirizine, astemizole and other drugs.

(6) Other drugs. There are mainly calcium channel blockers, potassium channel activators, inositol phosphate degradation inhibitors and vitamin drugs.