L3: Targets for drug action Flashcards
(21 cards)
What are the mechanisms of drug action (main targets for drug action)?
- Receptors
- Ion channels
- Enzymes
- Carrier molecules
What are receptors?
Receptors are protein macromolecules on the surface or within the cell that combines chemically with small molecules (ligands) and produce physiological regulatory functions.
What are the types of bonds between drugs and receptors?
1- The ionic bonds
2- The hydrogen bonds
3- The covalent bonds
What are the biological responses to drug-receptor binding?
1) Agonist effect
2) Antagonist effect
3) Partial agonist effect
What is an agonist?
The drug has both affinity and efficacy
What is the affinity of drugs?
it is the empathy of the receptor to the ligand.
What does affinity determine?
It determines the number of receptors occupied by the drug.
What is the efficacy of the drug?
It is the ability of a drug to produce a response (effect) after binding to the receptor.
What is efficacy measured by?
It is measured by the Emax(the maximal response that a drug can elicit at full concentration)
What is an antagonist?
the drug has affinity but no efficacy
What is a partial agonist effect?
Agonist gives submaximal response even at full concentration i.e never gives Emax.
What is a Graded response?
The response is increased proportionally to the dose of the agonist
ο e.g. the response of the heart to adrenaline.
What is a quantal response?
The response does not increase proportionally to the agonist but it is an all-or-none response
ο e.g. prevention of convulsions by antiepileptic drugs.
What is the importance of drug-response curves?
- Determination of potency
- Determination of efficacy
- determination of therapeutic index ( a measure of safety)
What is ED50 (effective dose)?
-the dose of the drug that gives 50% of the Emax, or it is the dose that gives the desired effect in 50% of a test population of subjects. A drug that gives ED50 in smaller doses is described as a βpotentβ drug.
What does TI equal?
LD50/ED50
-Drugs with high TI are safer for clinical use, and vice versa.
What does LD50 mean?
means the dose which is lethal to 50% of experimental animals
What does ED50 mean?
means the dose which is effective in 50 percent of animals
How do drugs affect ion channels?
ο Drugs could modulate ion channels e.g. Ion channels could be physically blocked by the drug molecule e.g. local anesthetics
How do drugs affect enzymes?
- The drug may act on the enzyme itself by competition with its normal substrate for the active binding sites on the enzyme.
- The drug molecule may inhibit the enzyme by covalent binding with the structure of the enzyme (irreversible binding).
What does it mean if there is a large difference between the dose of a drug that produces the desired effect and the dose that produces a toxic effect?
it is said that the drug has a large TI.
