2. Narcotic (opioid) analgesics. Classification. Mechanism of action. Side effects. Contraindications Comparative evaluation of drugs. Antagonists of narcotic analgesics.

MECHANISMS OF ANALGESIC ACTION OF NARCOTIC ANALGETICS

1. Inhibition of the conduction of pain impulses in the afferent pathways of the central nervous system (impaired transmission of impulses from the endings of the primary afferents to the intercalary neurons of the spinal cord).

2. Strengthening the inhibitory effect of the descending antinociceptive system on the conduction of pain impulses in the afferent pathways of the central nervous system.

3. Change in emotional assessment of pain.

SIDE EFFECTS 1. Nausea, vomiting; 2. Respiratory depression. 3. Bradycardia. 4. Intestinal colic, constipation. 5. Arterial hypotension. 6. With repeated use - addiction, drug dependence. 7. Retention of urination. 8. Increased intracranial pressure.

CONTRAINDICATIONS: 1. Children under 1 year old (morphine - for children under 3 years old). 2. Severe exhaustion. 3. Respiratory failure. 4. Traumatic brain injury (risk of cerebral edema). 5. Paralytic, spastic and obstructive gastrointestinal diseases. 6. Hypertrophy of the prostate gland. 7. Intracranial hypertension. 8. Pregnancy. 9. Fentanyl is contraindicated: during caesarean section (before fetal extraction) and other obstetric manipulations, severe hypertension in the pulmonary circulation, pneumonia, atelectasis, pulmonary infarction, bronchial asthma, parkinsonism (increases muscle stiffness). 10. Butorphanol and pentazocine are not prescribed for patients with coronary artery disease and heart failure.

Comparative characteristics of drugs.

Morphine - acts on the central nervous system, depresses the respiratory center, does not disturb the ventilation of the lungs, depresses the cough center, the vomiting center, stimulates the center of the vagus (bradycardia), increases smooth muscle tone, reduces intestinal secretion and urine output, reduces basal metabolism, causes hyperglycemia, lowers body temperature ...

Promedol is weaker than morphine in terms of analgesic effect, it inhibits the respiratory center less, does not affect uterine contractions during labor, does not spasm smooth muscles, it acts for 3-4 hours.

Fentanyl is 100 times more active than morphine in terms of analgesic effect, inhibits the respiratory center, pain relief after 1-3 minutes for 30 minutes, is used for neuraleptanalgesia.

Codeine - weak analgesic effect, inhibits the cough center, with prolonged use of constipation and dependence.

ANAGONISTS OF NARCOTIC ANALGETICS

Agonist antagonists - nalorphine (blocks μ- and stimulates κ- and δ-receptors)

Antagonists - naloxone, naltrexone (block all types of opioid receptors).

In case of poisoning with narcotic analgesics, respiratory depression is eliminated, all systemic effects of opioid analgesics, including euphoria, are eliminated, causing withdrawal symptoms in drug addicts.

Naloxone lasts for about 1-3 hours, and it must be re-injected, since narcotic analgesics work for a long time. Administered intravenously or intramuscularly. When administered intravenously, it normalizes breathing in 1-2 minutes. In addition, the drug is used for alcoholic coma, shock conditions, and some mental illnesses.

Naltrexone acts like naloxone, but for a longer period - up to 24-40 hours, is used orally, in tablets, the effect occurs after 1-2 hours.

Nalorphine is rarely used in case of an overdose of narcotic analgesics.