Adrenergic agonists are a group of drugs, 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 the localization, the mediated effect and the ability to form complexes with active substances. Alpha-agonists excitatory act on alpha-adrenergic receptors, causing a certain response of the body.
What are alpha-adrenergic receptors
A1-adrenergic receptors are located on the surface membranes of cells, in the area of synapses, they react to norepinephrine, which is released by the nerve endings of the postganglionic neurons of the sympathetic nervous system. Localized in the arteries of small caliber. Excitation of receptors causes vascular spasm, hypertension, decreased permeability of the arterial wall, decreasedmanifestations of inflammatory reactions in the body.
A2-adrenergic receptors are located outside the synapses and on the presynaptic membrane of cells. They respond to the action of norepinephrine and adrenaline. Excitation of the receptors causes a reverse reaction, which is manifested by hypotension and relaxation of blood vessels.
General information about adrenomimetics
Alpha- and beta-adrenergic agonists, which independently bind to receptors sensitive to them and cause the effect of adrenaline or norepinephrine, are called direct-acting agents.
The result of the influence of drugs can also occur by indirect action, which is manifested by stimulation of the production of its own mediators, prevents their destruction, and helps to increase concentration on nerve endings.
Adrenergic agonists 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 membranes of the eyes and nose;
- hypoglycemic coma;
- local anesthesia.
Alpha-agonists
The group of drugs includes selective (acting on one type of receptor) and non-selective (excitation of a1- and a2-receptors) agents. The non-selective alpha-agonist is represented directly by norepinephrine, which also has a stimulating effect on beta receptors.
Alpha-agonists that affect a1 receptors -anti-shock medicines used for a sharp decrease in blood pressure. They can be used topically, causing narrowing of the arterioles, which is effective for glaucoma or allergic rhinitis. Known drugs of the group:
- "Midodrine";
- "Mezatone";
- "Ethylephrine".
Alpha-agonists that affect a2 receptors are better known to the general population due to their widespread use. Popular representatives are Xylometazoline, Nazol, Sanorin, Vizin. Used in the treatment of inflammatory diseases of the eyes and nose (conjunctivitis, rhinitis, sinusitis).
Drugs are known for their vasoconstrictive effect, which allows you to eliminate nasal congestion. The use of funds should only take place under the supervision of a specialist, since prolonged uncontrolled use can cause the development of drug resistance and mucosal atrophy.
Young children are also prescribed drugs containing alpha-agonists. The preparations in this case have a lower concentration of the active substance. The same forms are used in the treatment of people suffering from diabetes and hypertension.
Alpha-adrenergic agonists that excite a2 receptors also include drugs of central action ("Methyldopa", "Clonidine", "Katapresan"). Their action is as follows:
- hypotensive effect;
- decrease in heart rateabbreviations;
- calming action;
- minor pain relief;
- decrease in secretion of lacrimal and salivary glands;
- decrease in water secretion in the small intestine.
Mezaton
A drug based on phenylephrine hydrochloride that causes an increase in blood pressure. Its use requires an accurate dosage, since a reflex decrease in heart rate is possible. "Mezaton" increases the pressure gently compared to other drugs, but the effect is longer.
Indications for use of the remedy:
- 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
A drug that has the same active substance, which is part of "Galazolin", "Otrivin", "Xymelin", "Dlyanos". It is used in local therapy of acute infectious rhinitis, sinusitis, hay fever, otitis media, in preparation for surgical or diagnostic interventions in the nasal cavity.
Produced as a spray, drops and gel for intranasal applications. The spray is allowed for use by children from 12 years of age. Prescribed with caution under the following conditions:
- angina;
- breastfeeding period;
- thyroid disease;
- prostatic hyperplasia;
- diabetes mellitus;
- pregnancy.
Clonidine
The drug is alpha-agonists. The mechanism of action of "Clonidine" is based on the excitation of a2-adrenergic receptors, resulting in a decrease in pressure, the development of a slight analgesic and sedative effect.
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 addiction.
"Clonidine" is contraindicated during pregnancy, however, in case of severe late gestosis, when the benefit to the mother outweighs the risk of harm to the fetus, it is possible to use small doses of the drug in combination with other drugs.
Vizin
Tetrizoline-based vasoconstrictor used in ophthalmology. Under its influence, the pupil expands, the swelling of the conjunctiva decreases, and the production of intraocular fluid decreases. Used in the treatment of allergic conjunctivitis, with mechanical, physical or chemical effects of foreign agents on the mucous membrane of the eyelids.
Alpha agonist overdose
Overdose is manifested by persistent changes that characterize the effects of alpha-agonists. The patient is worried about high blood pressure,increased heart rate with rhythm disturbances. During this period, a stroke or pulmonary edema may develop.
Overdose therapy consists of the following groups of drugs:
- Peripheral sympatholytics disrupt the transmission of nerve impulses in the periphery and in the nervous system. Thus, pressure decreases, heart rate and peripheral resistance decrease.
- Calcium antagonists are aimed at blocking the entry of calcium ions into cells. The heart muscle reduces the need for oxygen, its contractility decreases, relaxation during diastole improves, all groups of arteries expand.
- Myotropic drugs help to relax smooth muscles, including the muscular wall of blood vessels.
Alpha-agonists, the use of which has a large group of indications, require careful selection of dosage, monitoring of electrocardiogram, blood pressure, peripheral blood.
