Alpha-adrenomimetics: description, application, principle of action

Adrenomimetics call a group of medications, the result of which is associated with the stimulation of adrenoreceptors located in the internal organs and vascular walls. All adrenergic receptors are divided into several groups depending on localization, mediated effect and ability to form complexes with active substances. Alpha-adrenomimetics excitatory act on alpha-adrenergic receptors, causing a certain response of the body.

What is alpha-adrenergic receptors?

A1 adrenergic receptors are located on the surface membranes of cells in the synapse region, they react to norepinephrine, which is released by the nerve endings of the postganglionic neurons of the sympathetic nervous system. Localize in arteries of small caliber. The excitation of receptors causes vascular spasm, hypertension, a decrease in the permeability of the arterial wall, a decrease in the manifestations of inflammatory reactions in the body.

A2-adrenergic receptors are located outside the synapses and on the presynaptic membrane of the cells. React to the action of noradrenaline and adrenaline. The excitation of receptors causes a back reaction, which is manifested by hypotension and relaxation of blood vessels.

General information about adrenomimetics

Alpha- and beta-adrenomimetics, which independently bind to receptors sensitive to them and cause the effect of adrenaline or norepinephrine, are called direct agents.

The result of the influence of drugs can also occur indirectly, which is manifested by stimulating the development of their own mediators, hinders their destruction, and contributes to an increase in the concentration of nerve endings.

Adrenomimetics are assigned in the following states:

• Heart failure, severe hypotension, collapse, shock, cardiac arrest;
• Bronchial asthma, bronchospasm;
• Increased intraocular pressure;
• Inflammatory diseases of the mucous eyes and nose;
• Hypoglycemic coma;
• Local anesthesia.

Alpha-adrenomimetics

A group of drugs includes selective (acting on one type of receptor) and non-selective (excitation of a1 and a2 receptors) agents. Non-selective alpha-adrenomimetic is represented directly by norepinephrine, stimulating and acting on beta-receptors.

Alpha-adrenomimetics, which affect the a1 receptors, are anti-shock medications used for a sharp reduction in blood pressure. Can be used topically, causing a narrowing of arterioles, which is effective in glaucoma or allergic rhinitis. Known products of the group:

• "Midodrin";
• "Mesaton";
• "Ethylphrine."

Alpha-adrenomimetics affecting a2-receptors are more widely known to the general population due to widespread use. The most popular representatives are Xylometazoline, Nazol, Sanorin, Vizin. Used in the therapy of inflammatory diseases of the eyes and nose (conjunctivitis, rhinitis, sinusitis).

Drugs are known for their vasoconstrictive action, which allows you to eliminate nasal congestion. The use of drugs should occur only under the supervision of a specialist, since a prolonged uncontrolled reception can cause the development of drug resistance and mucosal atrophy.

Small children are also prescribed funds containing alpha-adrenomimetics. The preparations in this case have a lower concentration of the active substance. These same forms are used in the treatment of people with diabetes and hypertension.

Alpha-adrenomimetics, which excite a2-receptors, include the drugs of central action (Methyldopa, Clofelin, Catapresane). Their action is as follows:

• Antihypertensive effect;
• Decreased heart rate;
• Sedative effect;
• Insignificant anesthesia;
• Decrease in secretion of lacrimal and salivary glands;
• Decrease in secretion of water in the small intestine.

"Mezaton"

The drug is based on phenylephrine hydrochloride, which causes an increase in blood pressure. Its use requires an accurate dosage, since a reflex reduction in heart rate is possible. "Mesaton" raises the pressure gently compared with other drugs, but the effect is longer.

Indications for use of the drug:

• Arterial hypotension, collapse;
• Preparation for surgery;
• Vasomotor rhinitis ;
• Local anesthesia;
• Poisoning of various etiologies.

The need for immediate results requires intravenous administration. The drug is also injected into the muscle, subcutaneously, intranasally.

"Xylometazoline"

The drug that has the same active substance, which is part of the "Galazolin", "Otrivin", "Ximelin," "Foros." It is used in local therapy of acute infectious rhinitis, sinusitis, pollinosis, otitis, in preparation for operative or diagnostic nasal cavity interventions.

It is available in the form of a spray, drops and gel for intranasal applications. The spray is allowed for use by children from the age of 12. It is used with caution in the following conditions:

• Angina pectoris;
• The period of breastfeeding;
• Thyroid gland diseases;
• Hyperplasia of the prostate;
• diabetes;
• pregnancy.

"Cloffee"

The drug is alpha-adrenomimetics. The mechanism of action of "Clopheline" is based on the excitation of a2-adrenoreceptors, resulting in a decrease in pressure, the development of a minor analgesic and sedative effect.

It is widely used in various forms of hypertension, hypertensive crisis, to relieve an attack of glaucoma, in combination with other drugs for the treatment of drug and alcohol dependence.

"Clofelin" is contraindicated during pregnancy, but in the case of severe gestosis in later periods, when the benefit to the mother exceeds the risk of harm to the fetus, it is possible to use small doses of the medication in combination with other drugs.

"Vizin"

The vasoconstrictive drug based on tetrizoline, used in ophthalmology. Under its influence, the pupil dilates, the edema of the conjunctiva decreases, the intraocular fluid production decreases. Used in the treatment of allergic conjunctivitis, with mechanical, physical or chemical effects of foreign agents on the mucous lining.

Overdose with alpha-adrenomimetics

Overdose is manifested by persistent changes characterizing the effects of alpha-adrenomimetics. The patient is worried about high blood pressure, increased heart rate with rhythm disturbances. During this period, a stroke or lung edema may develop.

Overdose therapy consists of the following groups of drugs:

1. Peripheral sympatholytics disrupt the transmission of nerve impulses on the periphery and in the nervous system. Thus, the pressure decreases, the heart rate and the peripheral resistance decrease.
2. Calcium antagonists are directed at blocking the intake of calcium ions into cells. The cardiac muscle reduces the need for oxygen, reduces its contractility, improves relaxation during diastole, and expands all groups of arteries.
3. Myotropic drugs help to relax the smooth muscles, including the muscular wall of the vessels.

Alpha-adrenomimetics, the use of which has a large group of indications, require careful selection of dosage, monitoring of electrocardiogram, blood pressure, peripheral blood.