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Intrinsic activity (IA) and efficacy (E max) refer to the relative ability of a drug-receptor complex to produce a maximum functional response. This must be distinguished from the affinity, which is a measure of the ability of the drug to bind to its molecular target, and the EC 50, which is a measure of the potency of the drug and which is proportional to both efficacy and affinity.
Affinity describes how well a drug can bind to a receptor. Faster or stronger binding is represented by a higher affinity, or equivalently a lower dissociation constant. The EC 50 should not be confused with the affinity constant, K d. While the former reflects the drug concentration needed for a level of tissue response, the latter reflects ...
The affinity is a measure of how tightly a drug binds to the receptor. If the drug does not bind well, then the action of the drug will be shorter and the chance of binding will also be less. This can be measured numerically by using the dissociation constant K D. The value of K D is the same as the concentration of drug when 50% of receptors ...
Early forms of the receptor theory of pharmacology stated that a drug's effect is directly proportional to the number of receptors that are occupied. [14] Furthermore, a drug effect ceases as a drug-receptor complex dissociates. Ariëns & Stephenson introduced the terms "affinity" & "efficacy" to describe the action of ligands bound to receptors.
For example, assume that Drug A and Drug B are both protein-bound drugs. If Drug A is given, it will bind to the plasma proteins in the blood. If Drug B is also given, it can displace Drug A from the protein, thereby increasing Drug A's fraction unbound. This may increase the effects of Drug A, since only the unbound fraction may exhibit activity.
Allosteric modulators can alter the affinity and efficacy of other substances acting on a receptor. A modulator may also increase affinity and lower efficacy or vice versa. [ 4 ] Affinity is the ability of a substance to bind to a receptor .
Druggability is a term used in drug discovery to describe a biological target (such as a protein) that is known to or is predicted to bind with high affinity to a drug. Furthermore, by definition, the binding of the drug to a druggable target must alter the function of the target with a therapeutic benefit to the patient.
The dissociation constant is commonly used to describe the affinity between a ligand (such as a drug) and a protein; i.e., how tightly a ligand binds to a particular protein. Ligand–protein affinities are influenced by non-covalent intermolecular interactions between the two molecules such as hydrogen bonding , electrostatic interactions ...