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Analgesics

Analgetica

For medical students2 min readUpdated 2026-10-10

Analgesics are medications that selectively suppress or completely eliminate pain sensation, inducing a state of analgesia. Their key feature is the ability to act systemically without impairing the patient's conscious state or blocking other essential bodily functions.

Main GoalSelective elimination exclusively of pain sensations.
Type of ActionResorptive — drugs produce systemic effects only after absorption into the bloodstream.
CNS StatusIn therapeutic doses, the medications do not cause loss of consciousness.
MotilityThe patient's motor functions are completely preserved.

Pharmacological Profile of Analgesics

The action of analgesics is strictly resorptive in character. This means that for a clinical effect to develop, the drug must undergo absorption, enter the systemic circulation, and distribute throughout the body. Only then does the systemic analgesic effect develop.

A fundamental property of this group of drugs is their high specificity. Within strict therapeutic doses, they act selectively: pain sensation is the sole target.

During analgesic administration, the patient preserves:

Differential Diagnosis: How to Distinguish from Anesthetics

In clinical pharmacology, it is crucial to clearly differentiate analgesics from 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 (General Anesthesia Agents):

  1. Effect on consciousness. Analgesics never shut down the patient's consciousness, whereas general anesthetics purposefully induce a state of surgical anesthesia.
  2. Effect on sensation. General anesthetics totally suppress absolutely all types of sensation. Analgesics, conversely, suppress only the perception of pain.

Differences from Local Anesthetists: The difference here lies in the mechanism of blocking nerve impulses in a specific area. Local anesthetics work non-selectively: absolutely all types of sensation (pain, temperature, tactile) are blocked in the injection zone. Analgesics, by contrast, act selectively, eliminating only the pain itself.

Comparative Characteristics

For clarity, the main distinguishing features can be summarized in a simple structure:

ParameterAnalgesicsGeneral AnestheticsLocal Anesthetics
ConsciousnessPreservedEliminatedPreserved
Pain SensationSuppressedSuppressed (total)Suppressed (in the injection zone)
Other Sensation (tactile, temperature)PreservedDepressedBlocked (in the injection zone)
Type of EffectResorptive (systemic)SystemicLocal

Mnemonic

Remember the rule of the "Three P's" (or Three S's in Russian, adapted to English): Analgesics Save Consciousness, Save Motility, and Save Specific sensations (touch, temperature).

Frequently asked questions

What are the main pharmacological groups used to classify analgesics?

Analgesics are classified into two major groups depending on their site and mechanism of action.

  • Predominantly centrally acting agents — 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).
  • Predominantly peripherally acting agents.
What is the mechanism of action of narcotic (opioid) analgesics?

The mechanism of action of opioid analgesics involves the stimulation of opioid receptors. Analgesic and euphoric effects develop primarily due to the activation of $\mu$ (mu) receptors. Depending on the specific drug, they may 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 analgesic mechanism of non-narcotic analgesics (NSAIDs) is based on the inhibition of the cyclooxygenase (COX) enzyme. This leads to the blockade of prostaglandin synthesis (specifically $E_2$ and $I_2$) from arachidonic acid. Since pain syndromes are driven by prostaglandins, reducing their tissue concentration achieves a pronounced analgesic effect.

What specific adverse effects are characteristic of opioid analgesics?

Opioid analgesics are characterized by several specific adverse effects affecting the central nervous system and internal organs.

  • Respiratory depression — effect on the respiratory center.
  • Drug dependence — high abuse and addiction potential.
  • Euphoria — central adverse/psychotropic effect.
  • Decreased GI motility — development of constipation.
  • Increased tone of the urinary tract.
  • Hallucinations and aggressive behavior — upon $\kappa$ (kappa)-receptor stimulation.
Which drugs belong to the non-narcotic analgesic group?

Drugs utilized primarily as pain relievers include:

  • Metamizole sodium
  • Ketorolac

Acetylsalicylic acid (aspirin) belongs to NSAIDs with analgesic effects.

What is the core mechanism of action of analgesics?

Their core action involves the selective suppression or complete elimination of pain sensation to achieve analgesia.

Does a patient retain the ability to feel warmth or cold when taking these drugs?

Yes, temperature sensation, as well as tactile and proprioceptive sensation, are completely preserved at therapeutic doses.

How do analgesics differ from local anesthetics?

Local anesthetics non-selectively block all types of sensation in the application area, whereas analgesics act selectively only on pain.

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