Prescribing in specific circumstances

Question 1

Pharmacokinetics

Answer 1

The science of the rate of movement of drugs within biological systems, as affected by the absorption, distribution, metabolism, and elimination of medications

what your body does to the drug

important in the elderly

Question 2

Pharmacodynamics

Answer 2

Study of the biochemical and physiologic processes underlying drug action
Mechanism of drug action
Drug-receptor interaction
Efficacy
Safety profile

What the drug does to your body

Question 3

Bioavailability

Answer 3

Fraction of the administered dose of drug that reaches the systemic circulation
Expressed as letter F
Affected by many factors:

Drug factors
-Molecular weight / ionization

Absorption
-Gastric pH / health of GI tract

First pass metabolism (hepatic)

• Phenytoin may reduce F
• Grapefruit juice may increase F

Question 4

Apparent volume of distribution

Answer 4

• Artificial construct that if you give 100mg of drug and you measure the concentration as 10mg/L then it must have been put in 10L.
• It changes with age, renal function and hepatic function. Doesn’t changes much though