New Terms

Question 1

Bioavailability

Answer 1

Fraction (%) of an orally administered dose that reaches systemic circulation

Question 2

First Pass Effect

Answer 2

Efficient extraction by liver or gut wall
Amount reaching systemic circulation < amount absorbed
Large first pass effect = Low bioavailability

Question 3

Phase 1 Metabolism

Answer 3

1st stage of Hepatic metabolism
Catalysed by CYP450 mono-oxygenases
Drug oxidised/reduced/hydrolysed into intermediate metabolite = more readily accepted for Phase 2
Metabolites: More/Less active than parent drug
Other drugs may influence process by inducing or inhibiting CYP450 enzymes

Question 4

Phase 2 Metabolism

Answer 4

2nd stage of Hepatic Metabolism
Catalysed by substitute group transferases (e.g. glucuronyl transferase)
Water soluble (polar) moiety conjugated to drug metabolites to aid elimination by urine/bile
E.g. Glucuronyl, Sulfate, Acetyl, Methyl, Glycol

Question 5

Pro-Drug

Answer 5

Relatively inactive (precursor) 
After metabolism: metabolite more active than parent (inactive precursor) compound

Question 6

Apparent Volume of Distribution

Answer 6

Apparent Volume (L) required to account for all the drug in the body if it were present throughout whole body in same concentration as in the plasma sample

Question 7

Elimination Half Life

Answer 7

Time taken for 1/2 drug in body to be eliminated or for plasma concentration to fall by 1/2
After x5 half-lives drug virtually eliminated completely

Question 8

Zero Order Kinetics

Answer 8

Drug cleared at fixed rate = Fixed amount per unit time
Indicates mode of clearance (metabolism) is saturated
More commonly seen in OD but for some drugs can occur at low/therapeutic doses (Alcohol, Phenytoin)

Question 9

1st Order Kinetics

Answer 9

Exponential decline in plasma concentration
Higher concentration = More quickly eliminated
Most drugs

Question 10

Narrow Therapeutic Index

Answer 10

Effective dose + Toxic dose in close proximity

More susceptible to ADRs or environmental interference

Question 11

Tolerance

Answer 11

Diminished responsiveness to drug action

Decreased effect from constant dose or Increase in minimum dose required to produce given level of effect

Question 12

Physiological Dependence

Answer 12

Drug necessary for normal physiological functioning

Withdrawal reactions = Opposite of physiological effects of drug