Drug Distribution

Question 1

Bio availability

Answer 1

The amount of drug that reaches the reaches the circulation and is available for action

Question 2

Drug distribution

Answer 2

The reversible transfer of a drug between blood and the extra vascular fluid and tissues of the body.

Question 3

Factors that determine bio availability

Answer 3

1. Formulation and mode of administration
2. Ability of drug to pass physiological barriers
3. GI effects
4. First pass metabolism

Question 4

Factors that determine drug distribution

Answer 4

1. Plasma protein binding; only the unbound drug is biologically active.
2. Tissue distribution
3. Membrane characteristics
4. Transport mechanisms
5. Disease and other drugs
6. Elimination

Question 5

Tmax

Answer 5

Time to peak concentration

Question 6

Cmax

Answer 6

The peak concentration

Question 7

Vd

Answer 7

Apparent volume of distribution (L/Kg). The volume of plasma that would be necessary to account for the total amount of drug in a patients body, if that drug were present throughout the body at the same concentration as found in plasma. The greater the Vd the greater the ability of a drug to diffuse into/through membranes.

Question 8

Cl

Answer 8

Clearance (ml/min); the theoretical volume from which a drug is completely removed over a period of time i.e. elimination. Dependant on concentration and urine flow rate for renal clearance. Dependant on metabolism and biliary excretion for hepatic clearance.

Question 9

t1/2

Answer 9

half life; the time taken for the drug concentration in the blood to decline to half of the current volume.
t1/2 = 0.693Vd/Cl

Question 10

Selective accumlation

Answer 10

Drugs will not always be uniformly distributed to and retained by body tissues. The concentrations of some drugs will be either considerably higher or lower in particular tissues that could be predicted on the basis of simple distribution assumptions.

Question 11

Drug elimination

Answer 11

The removal of active drug and metabolites from the body. Determines length of action of drug.

Question 12

Location of drug metabolism

Answer 12

Liver

Question 13

Location of drug excretion

Answer 13

Usually kidney but also biliary system, gut and lung. `

Question 14

Renal drug excretion

Answer 14

1. Glomerular excretion/filtration
2. Active tubular secretion
3. Passive tubular re-absorption
   Renal disease will slow excretion and therefore reduce Cl of a drug allowing toxic levels to build up.