Pharmacological profile of analgesics
The action of analgesics is strictly resorptive in nature. This means that for a clinical effect to develop, the drug must undergo absorption, enter the systemic circulation, and distribute throughout the body. Only after this does the systemic analgesic effect develop.
A fundamental property of this group of medications is their high specificity. Within strict therapeutic dose limits, they work selectively: pain sensitivity becomes their sole target.
Against the background of analgesic use, the patient retains:
- Consciousness (there is no hypnotic or narcotic effect of CNS shutdown).
- Other types of sensitivity (the person continues to adequately perceive tactile touches, ambient temperature changes, and maintains proprioceptive sensitivity — the sense of body position in space).
- Motor functions (the ability to perform voluntary movements is not depressed).
Differential diagnosis: how to distinguish from anesthetics
In clinical pharmacology, it is extremely important to clearly differentiate between analgesics and drugs used for anesthesia. The main distinguishing criterion is the degree of selectivity of action and the effect on the central nervous system.
Differences from general anesthetics (narcotic drugs):
- Effect on consciousness. Analgesics never turn off the patient's consciousness, whereas general anesthetics purposefully induce a state of general anesthesia.
- Effect on sensitivity. General anesthetics totally depress absolutely all types of sensitivity. Analgesics, on the other hand, suppress only the perception of pain.
Differences from local anesthetics: The difference here lies in the mechanism of blocking nerve impulses in a specific area. Local anesthetics work unselectively: in the area of their administration, absolutely all types of sensitivity (pain, temperature, tactile) are blocked. Analgesics, conversely, act selectively, eliminating only the pain itself.
Comparative characteristics
For clarity, the main distinguishing features can be summarized in a simple structure:
| Parameter | Analgesics | General anesthetics | Local anesthetics |
|---|---|---|---|
| Consciousness | Preserved | Suppressed | Preserved |
| Pain sensitivity | Suppressed | Suppressed (totally) | Suppressed (in the administration area) |
| Other sensitivity (tactile, temperature) | Preserved | Depressed | Blocked (in the administration area) |
| Type of effect | Resorptive (systemic) | Systemic | Local |
Briefly: answers to topical questions
What are the main pharmacological groups into which analgesics are classified?
Analgesics are classified into two large groups depending on the localization and mechanism of action.
- Agents with predominantly central action — include opioid (narcotic) analgesics (agonists, partial agonists, agonist-antagonists), non-opioid drugs with analgesic activity, and mixed-action analgesics (combining opioid and non-opioid components).
- Agents with predominantly peripheral action.
What is the mechanism of action of narcotic (opioid) analgesics?
The mechanism of action of narcotic analgesics involves the stimulation of opioid receptors. Analgesic and euphoric effects develop primarily due to the activation of mu-receptors ($\mu$-receptors). Depending on the specific drug, they can act as full agonists, partial agonists (e.g., acting on $\mu$-opioid receptors), or agonist-antagonists.
What is the mechanism of the analgesic action of non-narcotic analgesics?
The mechanism of the analgesic action of non-narcotic analgesics (NSAIDs) is based on the inhibition of the cyclooxygenase (COX) enzyme. This leads to the blockade of the synthesis of prostaglandins (specifically, $E_2$ and $I_2$) from arachidonic acid. Since the pain syndrome is caused by the action of prostaglandins, a decrease in their concentration in tissues ensures the realization of a pronounced analgesic effect.
What specific side effects are characteristic of narcotic analgesics?
Narcotic analgesics are characterized by a number of specific side effects involving the central nervous system and internal organs.
- Respiratory depression — effect on the respiratory center.
- Drug dependence — high abuse potential.
- Euphoria — central side effect.
- Decreased GI motility — development of constipation.
- Increased tone of the urinary tract.
- Hallucinations and aggressive behavior — upon stimulation of kappa-receptors.
Which drugs belong to the group of non-narcotic analgesics?
Drugs used primarily as pain relievers include:
- Metamizole sodium
- Ketorolac
NSAIDs with an analgesic effect include acetylsalicylic acid (aspirin).
Remember the rule of the "Three S's" for analgesics: they Save Consciousness, Save Movement ability, and Save Specific types of sensitivity (warmth, touch).
Class and exam questions
What is the essence of how analgesics work?
The essence of their action lies in the selective suppression or complete elimination of pain sensitivity (achieving analgesia).
Does the patient retain the ability to feel heat or cold when taking these drugs?
Yes, temperature, as well as tactile and proprioceptive sensitivity, are completely preserved at therapeutic doses.
How do analgesics differ from local anesthetics?
Local anesthetics non-selectively block all types of sensation in the administration area, whereas analgesics act selectively on pain alone.
What else to study on this topic
- Resorptive drug action: phases and characteristics
- Proprioceptive, tactile, and temperature sensitivity
- Therapeutic doses and limits of selectivity of the pharmacological effect
- Comparative analysis of general anesthetics and analgesics
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