Sympathomimetics are a group of medicines that are used to treat bronchial asthma.
They are used on an emergency basis, if necessary, to stop spasms in the airways, but they are also used in basic therapy to reduce asthmatic manifestations and for prophylactic purposes.
What are sympathomimetics
During an attack of bronchial asthma , a spasm of smooth muscles in the bronchi occurs. Β2-adrenergic receptors located in the cells of the muscle layer are responsible for this.
Sympathomimetics are drugs that, by acting on these receptors, can expand the bronchi and increase patency. They are available in the form of aerosol cans for use in metered doses, tablets, injection solutions.
Classification of sympathomimetics
Another name for this class of drugs is indirect adrenomimetics . There are 2 targets for their action: β1-adrenergic receptors and β2-adrenergic receptors.
If a sympathomimetic acts on both types of receptors, it is called non-selective. With a selective action on β2-receptors, it is selective. In turn, this type is divided into long-acting and short-acting drugs.
Currently, they are less commonly used in the treatment of asthma. The reason was high mortality due to multiple side effects from the cardiovascular system – tachycardia, hypertension, cardiac arrhythmias. This is due to the fact that most of the β1 receptors are located in the heart. These include:
- isoprenaline ;
- orciprenoline .
They contribute to the expansion of the bronchi, stop the attack within 2-3 minutes.
They are the drugs of choice for the treatment of bronchial asthma. Their advantage is their quick effect.
Undesirable side effects are more likely to occur at high dosages.
Used to prevent and prevent asthma attacks. Their action lasts for 12 hours. These drugs are prescribed in combination with other drugs: glucocorticosteroids , mast cell stabilizers, leukotriene antagonists.
They are used in the form of an aerosol for inhalation therapy, the tablet form is indicated if it is impossible to use the inhaler correctly (children). Long-term remedies:
- formoterol fumarate ;
- salmeterol xinafoate .
In basic therapy, these drugs are included in order to reduce the dosage of glucocorticoids or if the desired effect is not achieved from their use.
β2-agonists are the gold standard for asthma treatment and are indicated for relieving bronchospasm. When using them, the effect of bronchodilation occurs after 5 minutes, lasts for 5-6 hours, so it makes no sense to take them as a prophylaxis.
It is recommended to use it no more than 4-5 times per day, if this amount is exceeded, the receptors stop responding, and there is no result from therapy. Most commonly prescribed:
- Salbutamol ;
- Terbutaline ;
- Levalbuterol .
The dose and frequency of application are selected according to an individual scheme.
Mechanism of action of sympathomimetic agents
Sustained-release sympathomimetics. The long-acting effect is due to the fact that the drug molecules have high lipophilicity . This feature allows them to enter the muscle cell and accumulate there.
If necessary, the active substance is released and interacts with the receptors of the bronchi, causing muscle relaxation.
Long-term exposure to the drug allows you to improve control over nocturnal attacks of asthmatic cough. The bronchoprotective effect helps to improve the functionality of the respiratory system .
Short-acting sympathomimetics. To provide first aid during suffocation in bronchial asthma, funds are needed that act instantly. The drugs have 2 mechanisms of action:
- They do not allow calcium ions into the cell, causing relaxation of smooth muscles. At the same time, the release of histamine, leukotrienes , which cause the development of an allergic reaction, is inhibited .
- They normalize the secretion of secretions in the bronchi and improve the excretion of mucus from the respiratory tract. They are able to prevent diseases and conditions caused by histamine-induced spasm: physical exertion, an attack when inhaling cold air.
The use of sympathomimetics in the treatment of bronchial asthma
The purpose of using selective sympathomimetics in the treatment of bronchial asthma is to relieve spasm of the bronchial muscles, improve their patency and avoid side effects.
Formoterol is a long-acting agent used to prevent asthma attacks. It is produced in an inhaler of 0.1 mg per dose, it is applied 2 times a day, or 0.2 mg is prescribed 3 times a day. Its action begins in 5 minutes, as with short-acting drugs. They tried to use this feature of the drug to relieve acute attacks, but deaths from bronchial asthma have become more frequent. Therefore, it is not recommended to use “on demand”.
Salmeterol is a bronchodilator with an anti-inflammatory effect. Reduces bronchial hyperreactivity, reduces their response to allergens. It is prescribed in a dose of 50 mcg 2 times a day. The effect appears after 40 minutes. The drug is approved for use in children over 4 years old. In studies, it was noted that with an isolated intake of salmeterol, the number of exacerbations and hospitalizations per year increased.
In this regard, adjustments were made to the BA treatment protocols for the use of prolonged-release drugs together with inhaled glucocorticoids. This is how the combined means were created. This made it possible to reduce side effects on the part of both groups, reduce the number of exacerbations of bronchial asthma, and enhance the result in the treatment of poorly controlled asthma.
Salbutamol is the drug of choice for eliminating an asthmatic attack, it is used mainly in the form of inhalation. Small bronchi reaches about 20% of the active substance. The maximum effect is achieved 20 minutes after application. In tablet form, it has a prolonged effect and is used to prevent nighttime exacerbations. Concomitant viral infections of the respiratory tract can reduce the therapeutic effect of salbutamol .
Fenoterol is a full β2-adrenergic receptor agonist. If you exceed a single or daily dose, the symptoms recur after a short time, a vicious circle occurs. This requires even more frequent use of the product.
Terbutaline – may enhance the effectiveness of other adrenergic agonists . Antiallergic and bronchodilator effect occurs within 30 minutes. It is used by inhalation , subcutaneously and in tablets.
Levalbuterol is a relatively new drug used to relieve airway obstruction in asthma. Intended for inhalation using a nebulizer: children over 6 years old are prescribed 0.63 mg 3 times / day, adults – 1.25 mg 3 times / day.
Isoprenaline – bronchodilator effect is achieved within 1-2 minutes and lasts 3-4 hours. It is prescribed in inhalation form with a concentration of 0.5% or 1%, 0.2 ml per dose. Tablets containing 0.005 mg of active substance are prescribed 3 times a day.
Orciprenoline – unlike isoprenaline , acts on β2-receptors more selectively, there are fewer side effects. Perhaps its intravenous use of 0.5-1 mg with a prolonged attack of bronchial asthma.
Most of the β2-adrenergic receptors are located in the bronchi. Asthma patients have more of them than healthy people. However, adrenergic receptors are found in other organs as well.
This is due to the manifestation of various side effects. In the left ventricle and right atrium, there are about 40% of the total number of receptors. With an increase in dosage and irrational use of sympathomimetics , disturbances in the work of the heart occur:
- atrial flutter;
- myocardial ischemia;
- heart failure;
- cardiomyopathy ;
- arrhythmia, including atrial fibrillation;
- ventricular fibrillation.
When acting on vascular receptors, their expansion and a sharp decrease in diastolic blood pressure are possible.
Stimulation of skeletal muscle receptors causes tremors, muscle weakness.
With the systemic use of sympathomimetics (subcutaneously, intravenously), metabolic disorders occur, which are manifested by an increase in the content of glucose, insulin, free fatty acids in the blood.
Side effects from the nervous system:
- sleep disorder;
- short-term convulsive states;
- disorder of taste.
- decreased appetite;
- dryness of the mucous membranes of the mouth.
Side effects in the respiratory tract: adrenomimetics can rarely cause increased bronchospasm after administration (fenoterol, salbutamol ), cough, inflammation of the nasopharynx.
Side effects are dose related and in most cases do not appear with moderate use. However, the risks increase during the provision of emergency care, when the dosage is exceeded 10 times within a few hours.
The possibility of using sympathomimetics is limited by a number of contraindications:
- Pregnancy and breastfeeding – No formal studies have been conducted with pregnant women. Restriction of use in pathological conditions of the fetus and mother: multiple pregnancy, intrauterine infection, anomalies in the development of the heart, eclampsia, uterine bleeding, placental abruption. The appointment is considered individually if the risk to the mother outweighs the risk to the fetus.
- Pathology of the heart and blood vessels – due to the possible influence and aggravation of the course of the disease, drugs from the group of sympathomimetics are not recommended for vascular atherosclerosis, tachyarrhythmias, angina pectoris, uncontrolled arterial hypertension, coronary insufficiency, heart defects, pulmonary hypertension.
- Others: pheochromocytoma, benign prostatic hyperplasia, intolerance or hypersensitivity to the drug, hyperthyroidism, severe liver disorders.
- Some sympathomimetics are absolutely contraindicated in the case of status asthmaticus : orciprenaline , levalbuterol , since the course of the disease may be complicated by their toxic effects on the heart.
Correct use of sympathomimetics significantly improves the quality of life of patients, helps in life-threatening conditions. The lack of effect in the treatment of bronchial asthma is most often due to insufficient dosage or improper use of the inhaler.
Unjustified frequent use leads to loss of sensitivity to the drug, lack of response. Side effects can lead to disability or death of the patient.