Anticholinergic drugs are drugs that block the action of the natural mediator - acetylcholine - on cholinergic receptors. In foreign literature, this group of medicinal substances is called "deliriants" due to the ability to cause delirium.
Some historical facts
Earlier, in the middle of the 20th century, anticholinergic drugs were used to treat chronic obstructive pulmonary disease and bronchial asthma, but they were supplanted by more modern drugs with fewer possible side effects. With the development of pharmacology, scientists have been able to develop anticholinergics that do not have the same huge list of side effects. Dosage forms have been improved, and anticholinergic drugs have again been used in the therapeutic practice of pulmonological diseases. The mechanism of action of this group of medicinal substances is rather complicated, but it is possible to describe the main links.
How do anticholinergics work?
The main action of an anticholinergic drug is to blockcholinergic receptors and the impossibility of influencing them with a mediator - acetylcholine. For example, receptors located in smooth muscles are blocked in the bronchi.
Classification of drugs
Depending on which receptors are affected by anticholinergic drugs, the list is divided into large groups:
- M-anticholinergics (atropine, scopolamine, ipratropium bromide).
- N-anticholinergics (pentamine, tubocurarine).
Depending on the selectivity of the action:
- Central, or non-selective (atropine, pirenzepine, platifillin).
- Peripheral or selective (ipratropium bromide).
M-anticholinergics
The main representative of this group of drugs is atropine. Atropine is an alkaloid found in some plants such as belladonna, henbane, and datura. The most pronounced property of atropine is antispasmodic. Against the background of its action, the tone of the muscles of the gastrointestinal tract, bladder, and bronchi decreases.
Atropine is administered orally, subcutaneously and intravenously. The duration of its action is about 6 hours, and when using atropine in the form of drops, the duration increases to seven days.
Pharmacological effects of atropine:
- Expansion of the pupils of the eyes due to the stimulating effect on the circular muscle of the iris - the muscles of the iris relax, respectively, the pupil expands. The maximum effect occurs 30-40 minutes afterinstillation.
- Accommodation paralysis - the lens stretches and flattens, anticholinergic drugs adjust the eye for far vision.
- Increased heart rate
- Relaxation of smooth muscles in the bronchi, gastrointestinal tract, bladder.
- Decreased secretion of internal glands such as bronchial, digestive and sweat glands.
Atropine use
- In ophthalmology: examination of the fundus, determination of the refraction of the eye.
- In cardiology, atropine is used for bradycardia.
- In pulmonology, anticholinergic drugs are used for bronchial asthma.
- Gastroenterology: with peptic ulcer of the stomach and duodenum, hyperacid gastritis (by reducing the secretion of hydrochloric acid by the digestive glands). The drug is effective for intestinal colic.
- In anesthesiologists, atropine is used as a premedication before various surgical interventions.
Side effects of atropine
Characterized by dry mouth and larynx, photophobia, impaired near vision, constipation, difficulty urinating.
Atropine is categorically contraindicated for use in glaucoma due to the effect of increasing intraocular pressure. Anticholinergic drugs are contraindicated for urinary incontinence, as they relax the muscles of the bladder. Cholinolytics need accuratedosage selection. If the dose is exceeded, poisoning of the body occurs, which is characterized by motor and emotional arousal, dilated pupils, hoarseness, difficulty in swallowing, and possibly an increase in temperature. With more severe poisoning, patients begin to lose orientation in space, cease to recognize the people around them, hallucinations and delusions appear. Perhaps the development of convulsions that turn into a coma, and due to paralysis of the respiratory center, death quickly occurs. Children are most sensitive to overdose - their lethal dosage is 6-10 mg.
Scopolamine is similar in structure to atropine, but unlike it, it has a predominantly depressing effect on the central nervous system, acting as a sedative. It is this property that is used in practical medicine - scopolamine is used for various disorders of the vestibular apparatus - dizziness, gait and balance disorders, to prevent the development of sea and air sickness.
Anticholinergic drugs are included in Aeron, which is often used before upcoming trips on planes and ships. The action of the tablets lasts about 6 hours. There is a non-tablet form - a transdermal therapeutic system - a patch that is glued behind the ear and releases the drug for 72 hours. These anticholinergic drugs - antidepressants, in especially advanced cases, help to quickly lift the mood of a patient who is chronically depressed.
Ipratropium bromide ("Atrovent") is a bronchodilator. When inhaled, it is practically not absorbed into the blood and does not have a systemic effect. Due to the blockade of cholinergic receptors of the smooth muscles of the bronchi, it expands them. These anticholinergics are available as an inhaler solution or metered-dose aerosol and are effective for asthma and COPD. Side effects include nausea and dry mouth.
Tiotropium bromides are anticholinergic drugs similar in properties to ipratropium bromide. Available as a powder for inhalation. A distinctive feature of this drug is that it acts on cholinergic receptors for a longer time, therefore it is more effective than ipratropium bromide. Used for COPD.
Platifillin - cross alkaloid. Unlike other anticholinergics, platifillin is able to dilate blood vessels. Due to this property, there is a slight decrease in blood pressure. The drug is produced in the form of a solution and rectal suppositories. It is used for spasms in the smooth muscles of internal organs, hepatic and renal colic, bronchial asthma, as well as for pain caused by spasm during exacerbation of gastric ulcer and duodenal ulcer. In ophthalmic practice, platifillin is used in the form of eye drops to dilate the pupils.
Pirenzepine - mainly blocks the cells of the stomach that release histamine. By reducing the secretion of histamine, the release of hydrochloric acid is reduced. In normal therapeutic doses, this drug has little effecton the pupils and heart contractions, so pirenzepine is mainly taken orally for the treatment of gastric and duodenal ulcers.
N-anticholinergics (ganglion blockers)
The mechanism of action is that anticholinergic drugs of this group block sympathetic and parasympathetic innervation at the level of nerve nodes, reduce the release of adrenaline and norepinephrine, and prevent the excitation of the respiratory and vasomotor center. Moreover, the greater the influence of sympathetic or parasympathetic innervation, the more the blocking effect will manifest.
For example, the size of the pupils is more influenced by parasympathetic innervation - as a rule, the pupils are usually constricted. In this case, anticholinergics will affect the parasympathetic nervous system - as a result, the pupils will dilate. Almost all blood vessels are under the influence of the sympathetic nervous system - drugs eliminate its influence and dilate blood vessels, thereby reducing pressure.
H-cholinergic blockers have a bronchodilatory effect and are used for bronchospasm, reduce the tone of the bladder, so these anticholinergic drugs can be prescribed for difficult urination. Additionally, these medicinal substances reduce the secretion of internal glands, and also slow down the peristalsis of the gastrointestinal tract. In medical practice, the hypotensive effect that these anticholinergic drugs have is mainly used. List of side effectsextensive:
- Gastrointestinal side: dry mouth and constipation.
- Respiratory system: cough, possible sensation of local irritation.
- From the CCC: arrhythmias, pronounced palpitations. These symptoms are rare and easily managed.
- Other effects: decreased visual acuity, development of acute glaucoma, edema.
Contraindications for the use of anticholinergics
- Increased sensitivity to atropine derivatives and other drug components.
- Pregnancy (especially 1st trimester).
- Lactation.
- Childhood (relative contraindication).
- The use of drugs in angle-closure glaucoma is absolutely contraindicated, in patients with renal insufficiency it is necessary to carefully monitor the condition of the blood and urine.
