Pharmacodynamic interaction
Pharmacodynamic interaction is realized at the level of the mechanism of action and effect manifestation, rather than by altering the substance concentration in the body.
The most common variant of this process is receptor interaction, which is based on competition for identical receptors. In the simultaneous presence of agonists (stimulants) and antagonists (blockers), a competition for binding sites develops.
Interaction in the adrenergic system
A striking example is the adrenergic system:
- Adrenoceptor blockers, such as phentolamine and propranolol, can significantly reduce or completely eliminate the physiological effects of stimulants (norepinephrine and isoprenaline).
- Sympatholytics, among which reserpine and guanethidine stand out, also participate in such processes.
Doxazosin: selective blocker
The drug doxazosin (known under trade names Cardura, Artesin, Camiren, Tonocardin) is a selective competitive blocker of postsynaptic α1-adrenoceptors.
The main feature of its pharmacodynamics is high selectivity: the drug's affinity for α1-receptors is exactly 600 times higher than for α2-adrenoceptors.
H2-histamine receptor blockers
This group of pharmacological agents is among the most effective and frequently used in clinical practice.
Mechanism of action:
- They block the effect of histamine, released by enterochromaffin-like cells, on the corresponding receptors.
- They reduce basal secretion of gastric juice at rest, during the day, and between meals.
- They reduce nocturnal acid production.
- They effectively inhibit pepsin production.
Blockers are receptor competitors: they occupy the sites of stimulants, reducing their effects.
Class and exam questions
What is the essence of the pharmacodynamic interaction of blockers?
It is realized at the level of the mechanism of action and effect, rather than substance concentration. Usually, this is competition between stimulators (agonists) and blockers (antagonists) for the same receptors.
What is the selectivity of doxazosin for adrenoceptors?
Doxazosin is a selective competitive blocker of postsynaptic α1-adrenoceptors. Its affinity for α1-receptors is 600 times higher than for α2-receptors.
How do H2-histamine receptor blockers affect secretion?
They block the effect of histamine, reduce basal daytime secretion, decrease nocturnal acid production, and inhibit pepsin output.
What else to study on this topic
- Differences between agonists and antagonists in receptor interaction
- Pharmacological effects of sympatholytics (reserpine, guanethidine)
- Trade names and analogs of doxazosin
- Comparison of affinity for α1 and α2 adrenoceptors
- The role of enterochromaffin-like cells in histamine production
- Features of basal and nocturnal hydrochloric acid secretion
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