Absorption and distribution of drugs

Question 1

What is absorption of drugs

Answer 1

It is the transfer of a drug from its site of administration to the bloodstream. The rate and efficiency of absorption depends on the route of administration.

Question 2

methods of Transport of a drug from the GI tract

Answer 2

1) Passive diffusion
2) active transport
3) endocytosis and exocytosis

Question 3

effect of pH on drug absorption

Answer 3

for acids: HA = H*+A-

for bases: BH* = B+H*

Question 4

Determination of how much drug will be found on either side of the membrane

Answer 4

pH = pKa + log{(nonprotonated species)/(protonated

species)}

Question 5

Physical fctors influencing absorption

Answer 5

1) blood flow to absorption site
2) total surface area available for absorption
3) contact time at the absorption surface

Question 6

Bioavailability

Answer 6

it is the fraction of administered drug that reaches the systemic circulation. It is expressed as the fraction of administered drug that gains access to the systemic circulation in a chemically unchanged form.

Question 7

determination of bioavailability

Answer 7

it is determined by comparing plasm levels of a drug after a particular route of administration. When the drug is given orally, only a part of administered drug appears in the plasma. By plotting plasma concentration of the drug versus time one can measure the Area Under Curve (AUC).

Question 8

Factors that influence bioavailability

Answer 8

1) First pass hepatic metabolism
2) solubility of the drug
3) chemical instability
4) nature of the drug formulation

Question 9

Bioequivalence

Answer 9

2 related drugs are bioequivalent if they show comparable bioavailability and similar times to achieve peak blood concentrations. 2 related drugs with a significant difference in bioavailability are said to be bioinequivalent.

Question 10

Therapeutic equivalence

Answer 10

2 similar drugs are therapeutically equivalent if they have comparable efficacy and safety.