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 "delirium" due to its ability to cause delirium.
Some historical facts
Earlier, in the mid-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 were able to develop such anticholinergics that do not have the previous huge list of side effects. Dosage forms were improved, and in the therapeutic practice of pulmonological diseases, anticholinergic drugs began to be used again. The mechanism of action of this group of drugs is rather complicated, but it is possible to describe the main links.
How do anticholinergic drugs work?
The main action of an anticholinergic drug is to block cholinergic receptors and the inability to expose them to a mediator - acetylcholine. For example, in the bronchi, receptors located in the smooth muscles are blocked.
Drug classification
Depending on which receptors are affected by anticholinergics, 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 that is found in some plants, such as belladonna, henbane, and dope. The most pronounced property of atropine is antispasmodic. Against the background of its action, the tone of the muscles of the gastrointestinal tract, bladder, bronchi decreases.
Atropine is prescribed 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:
- The 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 after instillation.
- Accommodation paralysis - the lens is stretched and flattened, anticholinergic drugs adjust the eye to distant vision.
- Heart rate
- Relaxation of smooth muscles in the bronchi, gastrointestinal tract, bladder.
- Decreased secretion of internal glands, such as bronchial, digestive and sweat.
Use of atropine
- In ophthalmology: fundus studies, determination of eye refraction.
- In cardiology, atropine is used for bradycardia.
- In pulmonology, anticholinergics are used for asthma.
- Gastroenterology: with peptic ulcer of the stomach and duodenum, hyperacid gastritis (due to decreased secretion of hydrochloric acid by the digestive glands). The drug is effective for intestinal colic.
- In anesthesiologists, atropine is used as a sedation before various surgical interventions.
Side effects of atropine.
Dry mouth and larynx, photophobia, impaired near vision, constipation, difficulty urinating are characteristic.
Atropine is categorically contraindicated in glaucoma due to the effect of increasing intraocular pressure. Anticholinergics for urinary incontinence are contraindicated, as they relax the muscles of the bladder. Anticholinergics need accurate dosage selection. When the dose is exceeded, poisoning of the body occurs, which is characterized by motor and emotional arousal, dilated pupils, hoarseness, difficulty swallowing, and possibly a temperature increase. With more severe poisoning, patients begin to lose their orientation in space, cease to recognize people around them, hallucinations and delusions appear. Perhaps the development of seizures that turn into a coma, and due to paralysis of the respiratory center, death quickly occurs. Children are most sensitive to excess doses - their lethal dosage is 6-10 mg.
Scopolamine is similar in structure to atropine, but in contrast, it has a predominantly depressing effect on the central nervous system, acting as a sedative. This property is used in practical medicine - scopolamine is used for various disorders of the vestibular apparatus - dizziness, impaired gait and balance, to prevent the development of sea and air sickness.
Anticholinergic drugs are included in the composition of the drug "Aeron", which is often used before upcoming trips on airplanes and ships. The action of the tablets lasts about 6 hours. There is a non-tabular form - the transdermal therapeutic system - a patch that sticks to the ear and releases the drug for 72 hours. These anticholinergic drugs are antidepressants, in especially advanced cases, they help to quickly raise the mood of a patient who is in chronic depression.
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. These anticholinergics are available as a solution for an inhaler or metered-dose aerosol, and are effective for asthma and COPD. Side effects are nausea and dry mouth.
Thiotropium bromides are anticholinergics similar in properties to ipratropium bromide. Available in powder form for inhalation. A distinctive feature of this drug is that it has a longer effect on cholinergic receptors, therefore it is more effective than ipratropium bromide. It is used for COPD.
Platifillin is an alkaloid of the cross. Unlike other anticholinergic blockers, platifillin is able to dilate blood vessels. Due to this property, a slight decrease in blood pressure occurs. The drug is released in the form of a solution and rectal suppositories. It is used for cramping in smooth muscles of internal organs, hepatic and renal colic, bronchial asthma, as well as for pain caused by spasm during exacerbation of peptic ulcer of the stomach and duodenum. In ophthalmic practice, platifillin is used in the form of eye drops to dilate the pupils.
Pirenzepine - predominantly blocks the cells of the stomach that secrete histamine. Due to the decrease in histamine secretion, the release of hydrochloric acid is reduced. In usual therapeutic doses, this drug has practically no effect on the pupils and heart contractions, therefore, mainly pirenzepine is taken orally for the treatment of peptic ulcer of the stomach and duodenum.
N-anticholinergics (ganglion blockers)
The mechanism of action is that anticholinergic drugs of this group block the 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 a blocking effect will manifest itself.
For example, the size of the pupils is more strongly affected by parasympathetic innervation - as a rule, the pupils are usually narrowed. In this case, anticholinergics will affect the parasympathetic nervous system - as a result, the pupils will expand. Almost all blood vessels are under the influence of the sympathetic nervous system - drugs eliminate its effect and expand the blood vessels, due to which the pressure decreases.
N-anticholinergic drugs have a bronchodilator effect and are used for bronchospasm, reduce the tone of the bladder, therefore, these anticholinergics can be prescribed for difficulty urinating. Additionally, these medicinal substances reduce the secretion of the internal glands, as well as slow down gastrointestinal motility. In medical practice, the hypotensive effect used by these anticholinergics is mainly used. The list of side effects is extensive:
- From the digestive tract: dry mouth and constipation.
- On the part of the respiratory system: cough, possibly a feeling of local irritation.
- From the CCC: arrhythmias, severe heartbeat. These symptoms are rare and can be easily eliminated.
- Other effects: a decrease in visual acuity, the development of an acute form of glaucoma, edema.
Contraindications to the use of anticholinergics
- Hypersensitivity to atropine derivatives and other components of drugs.
- Pregnancy (especially 1 trimester).
- Lactation.
- Children's age (relative contraindication).
- The use of drugs with angle-closure glaucoma is absolutely contraindicated; in patients with renal failure, it is necessary to carefully monitor the condition of blood and urine.