Pharmacokinetics

Question 1

Give a definition for Tachyphylaxis.

Answer 1

Reduction in substrate, causing a reduction in efficacy of the drug. (e.g. GTN: reduction in tissue sulfhydryl groups)

Question 2

Give a definition for Tolerance.

Answer 2

Reduction in receptors, causing a reduction in efficacy of the drug . (e.g. morphine: receptors become down-regulated, and salbutamol)

Question 3

Give a definition for Volume of Distribution.

Answer 3

This is the apparent volume into which the drug is distributed. It does not reflect an actual volume in the patient, but rather the volume that would be required to distribute the drug if it was homogenously distributed at the concentration present in plasma.

Question 4

What is drug biotransformation?

Answer 4

Metabolism of drugs to allow them to be excreted (e.g. more hydrophilic) and/or less active.

Question 5

Describe phase I and phase II reactions.

Answer 5

Phase I is the unmasking of a functional group, to make a more polar metabolite - usually hydrolysis, oxidation or reduction.

Phase II is the conjugation with endogenous substrate, to make it highly polar - e.g. glucuronidation, sulfation.

Question 6

What factors determine the Volume of Distribution of a drug?

Answer 6

Drug factors: Lipid solubility, protein-binding

Patient factors: Obesity, Age, Gender, Co-morbidities

(2 from each group to pass)