Week 13 / Pharmacology 3/Polypharmacy

Question 1

Q: What is drug antagonism in drug interactions?

Answer 1

A: Drug antagonism is an interaction between two drugs where the effect of one drug is diminished or completely abolished by the presence of the other drug.

Question 2

What are the types of drug antagonism are?

Answer 2

Competitive Antagonism
Non-Competitive Antagonism
Chemical Antagonism
Pharmacokinetic Antagonism
Physiological or Functional Antagonism

Question 3

Q: What is competitive antagonism in drug interactions?

Answer 3

A: Competitive antagonism occurs when the agonist and antagonist drugs compete for the same receptor binding site, with the antagonist reducing the chance of the agonist binding and producing an effect.

Question 4

Q: What are the two subtypes of competitive antagonism?

Answer 4

A: The two subtypes are:

Reversible (surmountable): The antagonist’s effect can be overcome by increasing the concentration of the agonist.

Irreversible (insurmountable): The antagonist binds permanently to the receptor, and its effect cannot be overcome by increasing the agonist concentration.

Question 5

Q: What happens in reversible competitive antagonism?

Answer 5

A: In reversible competitive antagonism, both the agonist and antagonist drugs bind reversibly to the receptor, and the fraction of receptors occupied depends on their relative concentrations and affinities.

Question 6

Q: Can reversible competitive antagonism be overcome?

Answer 6

A: Yes, the antagonism can be overcome by increasing the concentration of the agonist drug.

Question 7

Q: What effect does reversible competitive antagonism have on the agonist’s log D-R curve?

Answer 7

A: It causes a parallel shift to the right on the log D-R curve, with no reduction in the maximal response.

Question 8

Q: What happens in irreversible competitive antagonism?

Answer 8

A: In irreversible competitive antagonism, the antagonist binds irreversibly to the receptor, often due to high affinity or covalent bonding, rendering a fraction of receptors permanently unavailable for agonist binding.

Question 9

Q: Can irreversible competitive antagonism be overcome by increasing the agonist concentration?

Answer 9

A: No, the antagonism cannot be overcome by increasing the concentration of the agonist drug.

Question 10

Q: What effect does irreversible competitive antagonism have on the agonist’s log D-R curve?

Answer 10

A: It results in a reduction in the slope of the curve and a reduction in the maximal response.

Question 11

Q: What happens in non-competitive antagonism?

Answer 11

A: In non-competitive antagonism, the antagonist drug does not compete with the agonist for the same receptor binding site. Instead, it may bind to a different site on the receptor or interfere with response coupling.

Question 12

Q: Can non-competitive antagonism be overcome by increasing the agonist concentration?

Answer 12

A: No, the antagonism cannot be overcome by increasing the concentration of the agonist drug.

Question 13

Q: What effect does non-competitive antagonism have on the agonist’s log D-R curve?

Answer 13

A: Non-competitive antagonism leads to a reduction in the slope of the curve and a reduction in the maximal response.

Question 14

Q: What is chemical antagonism?

Answer 14

A: Chemical antagonism occurs when the antagonist drug directly interacts with the agonist drug, binding or combining with it in solution and rendering it inactive or unavailable to interact with its target receptors.

Question 15

Q: Can you give an example of chemical antagonism?

Answer 15

A: Yes, typical examples include protamine binding with heparin, and dimercaprol binding with heavy metals (Hg, Cu, Pb).

Question 16

Q: What is pharmacokinetic antagonism?

Answer 16

A: Pharmacokinetic antagonism occurs when the antagonist drug reduces the effective concentration of the active drug (agonist) at its site of action, altering its pharmacokinetics.

Question 17

Q: What are the possible mechanisms of pharmacokinetic antagonism?

Answer 17

A: The mechanisms include reduced absorption from the GIT, increased metabolic degradation, or increased renal excretion.

Question 18

Q: Can you provide an example of pharmacokinetic antagonism due to reduced absorption?

Answer 18

A: Yes, ferrous salts can reduce the absorption of tetracycline antibiotics.

Question 19

Q: Can you provide an example of pharmacokinetic antagonism due to increased metabolic degradation?

Answer 19

A: Yes, phenobarbital can increase the metabolic degradation of warfarin.

Question 20

Q: Can you provide an example of pharmacokinetic antagonism due to increased renal excretion?

Answer 20

A: Yes, sodium bicarbonate (NaHCO₃) can increase the renal excretion of aspirin.

Question 21

Q: What is physiological or functional antagonism?

Answer 21

A: Physiological or functional antagonism occurs when two opposing agonist effects cancel each other out by eliciting opposing responses through different receptors in a single biological system.

Question 22

Q: Can you provide an example of physiological antagonism with acetylcholine and noradrenaline?

Answer 22

A: Yes, acetylcholine and noradrenaline produce opposing effects on heart rate, where acetylcholine decreases heart rate, and noradrenaline increases it.

Question 23

Q: Can you provide an example of physiological antagonism with glucocorticoids and insulin?

Answer 23

A: Yes, glucocorticoids increase blood sugar levels, while insulin decreases them, leading to opposing effects on blood sugar regulation.

Question 24

Q: What is summation in drug interactions?

Answer 24

A: Summation occurs when the combined effect of two drugs, which elicit the same overt response, is equal to the algebraic sum of their individual effects, regardless of their mechanism of action.

Question 25

Q: What is additivity in drug interactions?

Answer 25

A: Additivity occurs when the combined effect of two drugs, which act by the same mechanism, is equal to the expected sum of their individual effects.

Question 26

Q: What is synergism or potentiation in drug interactions?

Answer 26

A: Synergism or potentiation occurs when the combined effect of two drugs is greater than the algebraic sum of their individual effects.

Question 27

Q: How can a synergist drug act to enhance the effect of another drug?

Answer 27

A: A synergist may act to:

Increase the concentration of the other drug at its receptor sites (e.g., tyramine & MAO inhibitors)
Increase the responsiveness of the other drug’s receptor-effector protein (e.g., benzodiazepines & GABA at the GABA receptor)