Lecture 20: Drug Interactions

Question 1

Pharmacodynamic interaction of Atenolol (β antagonist) & Salbutamol (β2-agonists)

Answer 1

Antagonism: β-receptor antagonists reduce the effectiveness of β2-agonists.

Question 2

Pharmacokinetic Interaction of Cimetidine

Answer 2

Altered Metabolism: Enzyme inhibition: increased risk of bleeding.

Question 3

Pharmacokinetic Interaction of Iron

Answer 3

Altered Gastrointestinal Absorption:

Iron or antacids containing aluminum or calcium can chelate tetracycline & reduce its absorption and effectiveness.

Question 4

Pharmacokinetic Interaction of Phenobarbital

Answer 4

Altered Metabolism:

Enzyme induction → (inducers) accelerate the metabolism of many drugs.

Question 5

Pharmacokinetic Interactions of Probenecid

Answer 5

Altered Renal Elimination (Excretion):

Inhibition of active tubular secretion (important and beneficial).

Question 6

Pharmacokinetic Interactions of Salicylate

Answer 6

-Altered Renal Elimination (Excretion)
●Inhibition of tubular re-absorption via changing the ratio of non-ionized to ionized fractions by altering pH of the urine.
E.g. making urine alkaline to increase excretion of salicylates (aspirin).

Question 7

Pharmacodynamic interaction of Salicylate

Answer 7

-Additive effect

●Increased risk of bleeding when aspirin is co-administered with the anticoagulant warfarin

Question 8

Pharmacokinetic Interaction of Tetracyclines

Answer 8

-Altered Gastrointestinal Absorption

●Iron or antacids containing aluminum or calcium can chelate tetracycline & reduce its absorption and effectiveness.

Question 9

Interaction of Diet and Drugs of Tetracyclines

Answer 9

Tetracycline with milk products (Ca 2+) resulting in decreased absorption of the antibiotic.

Question 10

Pharmacokinetic Interaction of Warfarin (Altered Drug Distribution)

Answer 10

-Displacement from protein binding sites:
●Many drugs are highly bound to plasma proteins.
●Displacement from protein binding sites by other drugs increases the concentration of free form of the object drug leading to increased pharmacological activity.

Question 11

Pharmacokinetic Interaction of Warfarin (Altered Metabolism)

Answer 11

• Enzyme induction

- Enzyme inhibition: increased risk of bleeding

Question 12

Pharmacodynamic interaction of Warfarin

Answer 12

-Additive effect

●Increased risk of bleeding when aspirin is co-administered with the anticoagulant warfarin