Chemical structure and pharmacological properties
In its chemical structure, isoprenaline (also known as isadrin or isoproterenol) is N-isopropylnoradrenaline.
The main feature of its mechanism of action is that it is a direct non-selective $\beta$-adrenoreceptor agonist. This means that the drug simultaneously and actively stimulates both receptor subtypes:
- $\beta_1$-receptors (located predominantly in the heart);
- $\beta_2$-receptors (mediating the bronchodilatory effect).
Clinical application
The scope of medical use of isoprenaline covers two main directions:
- In pulmonology: the drug is used as a bronchodilator (for this purpose, special aqueous solutions for inhalation and lozenges are used).
- For conduction disorders: the medication is prescribed to improve AV conduction in atrioventricular block (in the form of sublingual tablets placed under the tongue).
Nevertheless, in modern clinical practice, the drug is inferior as a bronchodilator to newer selective $\beta_2$-adrenoreceptor agonists due to a less favorable safety profile.
Side effects and cardiac risks
Since isoprenaline non-selectively stimulates all beta-adrenoreceptors, its side effects are divided into two groups:
- The effects of $\beta_2$-receptor activation are similar to the effects of salbutamol.
- Cardiac side effects from $\beta_1$-receptor stimulation are significantly more pronounced than those of selective drugs.
Main cardiovascular risks:
- Onset of pronounced tachycardia.
- Significant increase in myocardial oxygen demand.
- High probability of developing arrhythmias.
Development of tolerance
With prolonged use of any $\beta$-adrenoreceptor agonists (both selective and non-selective), tolerance inevitably develops—a gradual decrease in the therapeutic effect when using the previous dose of the drug (habituation).
The underlying mechanism involves:
- Desensitization (decreased sensitivity) of the receptor apparatus.
- Reduction in receptor density and number on cell membranes.
Process dynamics:
- Tolerance develops first to various side effects (such as tremor or tachycardia).
- With some delay, a decrease in the therapeutic (bronchodilatory) effect occurs.
Briefly: answers to topical questions
What are the possible routes of administration of isoprenaline into the body?
Possible routes of administration of isoprenaline indicated in the sources:
- Sublingual route — tablets under the tongue are used to improve atrioventricular conduction in AV block.
- Inhalation route — aqueous solutions for inhalation are used in pulmonology as a bronchodilator.
- Lozenges are also indicated as a form of application in pulmonology.
What side effects of isoprenaline are caused by beta-2 adrenergic receptor stimulation?
The side effects of isoprenaline caused by $\beta_2$-adrenoreceptor stimulation are described in the sources as similar to the effects of salbutamol.
It is also noted for $\beta$-adrenoreceptor agonists that with prolonged use, tolerance develops first to side effects such as tremor and tachycardia.
Iso-PREN-aline: PRENess the heart to tachycardia and arrhythmia due to a non-selective hit on both types of beta-receptors.
Class and exam questions
What is the mechanism of action of isoprenaline?
Isoprenaline is a direct non-selective $\beta$-adrenoreceptor agonist. It equally stimulates both $\beta_1$ and $\beta_2$ adrenergic receptors.
Why does isoprenaline lose to modern bronchodilators?
As a bronchodilator, it is inferior to modern selective $\beta_2$-adrenoreceptor agonists due to a poorer safety profile and pronounced cardiac side effects.
What is the essence of tolerance to $\beta$-adrenoreceptor agonists?
Tolerance develops with prolonged use of drugs and manifests as a decrease in the effect from the previous dose. This occurs due to receptor desensitization and a decrease in their density on membranes.
What else to study on this topic
- The role of Gq-proteins and smooth muscle contraction
- Dosage forms for sublingual and inhalation use
- Comparison of safety profiles with salbutamol
- Molecular mechanisms of receptor desensitization
- Pharmacokinetics and chemical structure features of N-isopropylnoradrenaline
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