Mechanism of Action and Receptor Profile
The pharmacological activity of the drug is based on its dual interaction with the central nervous system receptor system.
As an agonist, it stimulates $\kappa$- (kappa) and $\delta$- (delta) opioid receptors. This mechanism is responsible for producing analgesia. However, its analgesic potency is significantly lower than that of classical Morphinum. At the same time, the drug causes less respiratory depression.
Simultaneously, the agent acts as a $\mu$- (mu) receptor antagonist. Blocking these structures means the drug does not induce euphoria, and the overall risk of drug dependence is notably lower. However, kappa-receptor stimulation carries its own risks and can provoke dysphoria.
Interaction with Full Agonists
When co-administered with full opioid agonists (e.g., morphine), the drug acts as a competitive antagonist. It can physically displace full agonists from their receptor binding sites.
This poses a major clinical danger to individuals with pre-existing opioid dependence: administering the drug instantly precipitates an acute withdrawal syndrome.
Pharmacokinetics
The drug is well absorbed via all routes of administration. It can be administered enterally (orally) or parenterally (subcutaneously, intramuscularly, intravenously).
Onset of action strictly depends on the route of delivery:
- Intravenous: onset within 2–3 minutes, peak achieved in 15–30 minutes.
- Intramuscular and oral: onset in 15–30 minutes, peak at 30–60 minutes.
The total duration of the therapeutic effect is up to 3 hours.
Effects on the Cardiovascular System
The drug has a pronounced stimulating effect on hemodynamics. It increases pulmonary artery pressure, preload, and cardiac workload. In addition, its administration is accompanied by tachycardia and elevated blood pressure.
Due to the risk of critical myocardial overload, the drug is not recommended for use in patients with myocardial infarction.
Side Effects and Contraindications
Specific central nervous system side effects include dysphoria and hallucinations.
Absolute contraindications for prescribing include:
- Bronchial asthma;
- Traumatic brain injury (TBI);
- Epilepsy;
- Cholelithiasis and urolithiasis;
- Severe hepatic and renal impairment.
There are also strict limitations on its use during pregnancy, lactation, and in children under 1 year of age.