Mechanism of action and classification
Analeptics restore body function by exciting the vital centers of the medulla oblongata. Depending on how the drugs transmit the stimulating signal, they are divided into three main groups:
- Direct-acting. Directly activate centers in the brain. This group includes pentetrazol and bemegride.
- Reflex-acting. Excite n-cholinergic receptors located in the carotid sinus zone. From there, nerve impulses are reflexively directed to the medulla oblongata. Representatives: cytisine and lobeline.
- With a mixed mechanism. Combine both pathways of stimulation (both direct and reflex). A typical example is nikethamide.
In addition, drugs differ in their safety profile. For example, caffeine has a relatively large therapeutic window, whereas strychnine has a narrow one, which requires high caution when prescribing it.
Features of action of individual representatives
Different analeptics have their own specific "targets" in the nervous system, which determines the features of their clinical use:
- Strychnine predominantly stimulates the spinal cord.
- Caffeine has a greater effect on the cerebral cortex and subcortical structures.
- Sulfocamphocaine acts selectively, stimulating only the medulla oblongata.
In terms of the strength of their stimulating effect on the CNS, drugs can be arranged in descending order:
- Pentetrazol (Corazole)
- Bemegride
- Strychnine
- Caffeine
- Sulfocamphocaine
- Nikethamide (Cordiamine)
- Methylamide ethylimidazole dicarboxylate (Ethimizole)
Pharmacological effects and indications
The main result of analeptic action is enhanced respiration and blood circulation. Indirectly, they contribute to the restoration of renal function and also accelerate the biotransformation and elimination of toxic substances with narcotic properties from the body.
In clinical practice, analeptics are used for the following conditions:
- Asphyxia in newborns.
- Shock, collapse, and severe hypotension.
- Depression of vital centers of various etiologies.
- As antagonists in overdose of general anesthetics and hypnotic drugs.
Important clinical nuance: the best therapeutic effect is achieved not by increasing the dose of a single drug, but by the combined use of various analeptics in small doses.
Side effects and contraindications
The use of CNS stimulants is always associated with the risk of adverse reactions. The main side effects of analeptics include:
- Dyspeptic disorders: nausea and vomiting.
- Neurological disorders: involuntary muscle twitching.
- Severe complications: overdose causes pronounced convulsive syndrome (seizures).
Special attention is required for bemegride. Despite the fact that analeptics are generally used as antagonists of hypnotics, bemegride is contraindicated in severe poisonings with hypnotic drugs. This is due to the pathophysiology of the process: the drug sharply increases oxygen consumption by brain neurons. If hypoxia, characteristic of severe poisoning, has not been eliminated, such metabolic stimulation will only exacerbate nerve cell damage.
Place in respiratory therapy
In the general classification of pharmacological agents affecting the respiratory system, five main categories are distinguished. Analeptics act as respiratory stimulants.
To understand their place in therapy, it is important to distinguish them from other groups:
- Antitussive drugs are aimed at suppressing the cough reflex.
- Expectorants improve the elimination of sputum from the respiratory tract.
- Bronchodilators widen the lumen of the bronchi.
- Surfactant preparations affect surface tension in the alveoli.
Briefly: answers to topical questions
What dosages and dosage forms do analeptics have?
The best effect is achieved with the combined use of various analeptics in small doses. For bemegride, use is indicated as a 0.5% solution: 10 ml intravenously slowly, repeatedly, as an antidote in barbiturate poisoning.
To memorize direct-acting drugs, use the mnemonic: Pentetrazol and Bemegride strike right into the Bulbus (medulla oblongata).
Class and exam questions
Why should bemegride not be used in severe hypnotic poisoning?
Severe poisoning leads to pronounced hypoxia. Bemegride stimulates neuronal metabolism and increases their oxygen demand, which under conditions of uncorrected oxygen starvation leads to even greater damage to brain cells.
How to achieve the maximum effect from analeptics with minimal risk?
The best clinical result is provided by the combined use of several different analeptics in small doses, rather than using a single drug in a high dosage.
Which analeptic has the narrowest therapeutic window?
Strychnine. It requires the strictest dosage control, since the slightest excess can cause severe convulsions due to powerful stimulation of the spinal cord.
To which group of drugs affecting the respiratory system do analeptics belong?
In the classification of agents affecting the respiratory system, analeptics (such as nikethamide and caffeine) are isolated into a separate group of respiratory stimulants.
What else to study on this topic
- Comparative profile of the therapeutic width of caffeine and strychnine
- Mechanism of excitation of n-cholinergic receptors of the carotid sinus zone by cytisine and lobeline
- Pathophysiology of convulsive syndrome in analeptic overdose
- Interaction of analeptics with hypnotics and general anesthetics
- The role of analeptics in complex therapy of shock and collapse
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