4.10:
Dose-Response Relationship: Selectivity and Specificity
Different types of receptors are expressed throughout the body. The interaction of these receptors with drug molecules may lead to a pharmacologic response.
Drug–receptor interactions are characterized by selectivity and specificity.
Drug specificity is the ability of a drug to interact with only a specific target.
For example, in the parietal cells of the stomach, omeprazole inhibits the proton pump and decreases acid secretion into the stomach lumen.
In contrast, drugs like amiodarone have low specificity as they interact with multiple targets in the body, including receptors, enzymes and ion channels. Such off-target interactions can lead to several adverse effects beyond the drug's primary action.
Drug selectivity describes the strong preference of a drug for its intended receptor over other receptors.
For instance, consider two β-adrenergic agonists, isoprenaline and salbutamol.
As isoprenaline is a nonselective β agonist, it can stimulate β-1 receptors of the heart and β-2 receptors of the bronchioles. This increases the heart rate and relaxes the bronchial muscles.
In comparison, salbutamol is a selective β agonist with a higher affinity for the β-2 receptors, causing bronchodilation.
4.10:
Dose-Response Relationship: Selectivity and Specificity
Drugs exert their therapeutic effects by interacting with receptors, enzymes, or ion channels that are present throughout the human body. The strength and duration of the interaction between a drug and its target receptor are characterized by the selectivity and specificity of the drug. Selectivity refers to a drug's strong preference for its intended target over other targets. For instance, isoprenaline, a non-selective β-adrenergic agonist, interacts with both β1– and β2-adrenergic receptors in the heart and smooth muscle tissues, respectively. Due to its lack of selectivity, it can stimulate receptors for both cardiac and bronchial effects. The nonselective nature of isoprenaline makes it less ideal for treating asthma. On the other hand, salbutamol is a selective β2-adrenergic agonist that is commonly used to treat asthma. Its selectivity for β2-adrenergic receptors allows it to specifically target the smooth muscle cells in the bronchioles, causing bronchodilation and relieving asthma symptoms.
Specificity describes the extent to which a drug produces only the desired therapeutic effect without causing any other physiological changes. A drug with high specificity exhibits a strong drug–receptor interaction, ensuring targeted action and minimal side effects. In contrast, drugs with low specificity may produce unintended consequences due to their weak drug-receptor interaction. For example, amiodarone, an antiarrhythmic drug, demonstrates low specificity, affecting multiple ion channels and causing various side effects. On the other hand, omeprazole, a proton-pump inhibitor, shows high specificity by selectively inhibiting gastric acid secretion without impacting other physiological processes.