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Respiratory Stimulants

Stimulantia respiratoria

For medical students2 min readUpdated 2026-10-10

Respiratory stimulants are a pharmacological group of drugs used to restore respiratory function during pathological depression. They act on the respiratory center either directly or indirectly, helping the body cope with the effects of anesthesia or mild poisoning.

Central actionBemegride and caffeine (classified as analeptics)

Reflex actionLobeline and cytisine (classified as nicotinic receptor agonists)

Strict contraindicationSevere poisoning with profound depression of the respiratory center

Sites of actionDirectly on the respiratory center or carotid bodies

Main Indications for Respiratory Agents

In clinical pharmacology, several groups of pathological conditions require the administration of drugs affecting the respiratory system. The choice of a specific drug class depends strictly on the nature of the pathology:

In respiratory depression, direct respiratory stimulants and specific antagonists of the depressant agents are used.
If the patient suffers from a cough, doctors prescribe expectorants (to improve sputum clearance) and antitussives.
In bronchial asthma, therapy is based on bronchodilators, as well as anti-inflammatory and antiallergic drugs.
In the case of respiratory failure and acute respiratory distress syndrome (ARDS), the primary indication is the administration of surfactant preparations.

Classification of Respiratory Stimulants

Drugs that restore depressed breathing are classified into three main groups based on their mechanism of action on the nervous system:

Central action. This group includes bemegride (Bemegridum) and caffeine (Coffeinum). Pharmacologically, they are analeptics.
Reflex action. The main representatives are lobeline (Lobelinum) and cytisine (Cytisinum). Structurally and functionally, they are nicotinic (N)-cholinomimetics.
Mixed action. This category includes nikethamide (Nikethamidum), widely known in clinical practice by the trade name Cordiamine.

Pharmacology of Analeptics (Central and Mixed Action)

Drugs such as nikethamide, bemegride, and caffeine exert a direct stimulation of the respiratory center. Their key pharmacodynamic effect is the ability to effectively reduce the inhibitory influence of hypnotics and general anesthetics on the respiratory center.

Main indications for use:

Mild poisoning with hypnotics or narcotic analgesics.
Postoperative period (administered to rapidly restore adequate breathing after anesthesia).

The route of administration for these drugs is exclusively parenteral (intravenous or intramuscular).

Important aspect: contraindications and limitations Analeptics are strictly contraindicated in severe poisoning. The pathogenesis involves the following physiological mechanism: in profound nervous system depression, breathing is not restored by these drugs. However, neuronal stimulation dramatically increases the brain's oxygen demand. Under conditions of inadequate ventilation, this only worsens hypoxia and significantly worsens the patient's prognosis.

Features of Reflex Respiratory Stimulants

Lobeline and cytisine operate via a completely different pharmacological principle. The primary site of their action is the sinocarotid zone, specifically the carotid bodies.

The mechanism of action unfolds in three consecutive steps:

Activation of nicotinic acetylcholine receptors located in the carotid bodies.
This causes a marked increase in afferent nerve impulses traveling via neural pathways to the medulla oblongata.
As a result, secondary (indirect) excitation of the respiratory center occurs.

Efficiency limitations: Based on this mechanism, these drugs have clear limitations. They are entirely ineffective in two clinical situations: if the patient's reflex arc is physically disrupted, or if the respiratory center is profoundly depressed and incapable of adequately responding to incoming afferent impulses.

Mnemonic

To quickly memorize the classification, use the acronyms based on initial letters: Central — Bemegride, Caffeine (CBC). Reflex — Lobeline, Cytisine (RLC). Mixed — Nikethamide (MN).

Frequently asked questions

Which specific drugs act as antagonists in respiratory depression?

Specific antagonists for drug-induced respiratory depression include opioid and benzodiazepine receptor antidotes. Clinical examples include:

Naloxone — administered intravenously, acts for up to 1 hour, displaces opioids from the respiratory center.
Naltrexone — administered orally, duration of action up to 36 hours.
Flumazenil — administered via IV infusion, competitive antagonist of benzodiazepine receptors, effective in classic benzodiazepine and Z-drug overdose.

What side effects are characteristic of analeptic overdose?

Analeptic overdose causes dyspeptic and neurological disorders, as well as more severe central nervous system complications:

Dyspeptic disorders — nausea and vomiting.
Neurological disorders — muscle twitching.
Severe complications — development of seizures (convulsions).

Which pharmacological groups are used to treat bronchial asthma?

Bronchodilators, anti-inflammatory drugs, and antiallergic agents are used to treat bronchial asthma. Main groups include:

Bronchodilators — muscarinic antagonists, beta-2 agonists, and phosphodiesterase inhibitors for relieving bronchospasm.
Glucocorticoids — baseline anti-inflammatory therapy (including inhaled forms).
Mast cell stabilizers — cromones, used exclusively for prophylaxis.
Leukotriene receptor antagonists — baseline anti-leukotriene therapy.
Biologics — monoclonal antibodies used as add-on therapy for severe cases.

Why are analeptics extremely dangerous in severe hypnotic poisoning?

During profound depression, they cannot trigger spontaneous breathing while forcing neurons to consume more oxygen. This inevitably leads to severe cerebral hypoxia.

To which pharmacological group do lobeline and cytisine belong?

They are classified as nicotinic receptor agonists. They stimulate respiration not directly, but reflexively by acting on receptors in the carotid bodies.

In which cases do reflex-acting drugs fail to work?

They will have no effect if the patient's reflex arc is damaged or if the respiratory center is in a state of profound depression so severe that it cannot process incoming impulses.

Go deeper

Antagonists of respiratory depressants (specific antidotes and principles of their use).
Pharmacology of expectorants and antitussives.
Bronchodilators and anti-inflammatory drugs in the complex therapy of bronchial asthma.
Surfactant preparations in respiratory failure and acute respiratory distress syndrome (ARDS).