2 - Drug movement in the body/ Drug Disposition

Question 1

define distribution?

Answer 1

the process by which a drug leaves the circulation and enters the tissues perfused by the blood. Once within a tissue further, blood-independent, distribution may occur (or carrier- mediated transport)

Question 2

define metabolism?

Answer 2

the process by which tissue enzymes (principally in the liver - hepatic metabolism) catalyse the chemical conversion of a drug to a more polar form that is more readily excreted from the body

Question 3

____ drugs are more readily excreted by the body?

Answer 3

polar

Question 4

where is the principle site for excretion?

Answer 4

the kidneys

Question 5

where is the interstitial fluid?

Answer 5

fluid between cells

Question 6

___ absorbs very little apart from ethanol

Answer 6

stomach

Question 7

partition coefficient
the ratio of the concentrations of a solute in two _____ or slightly _____ liquids, or in two ____, when it is in ______ across the interface between them

Answer 7

partition coefficient
the ratio of the concentrations of a solute in two immiscible or slightly miscible liquids, or in two solids, when it is in equilibrium across the interface between them

Question 8

drugs must ___ in order to release the active drug molecule

Answer 8

dissolve

Question 9

absorption of a drug occurs by ___ ____ across membranes - although some agents are ____ .

Answer 9

simple diffusion, transported

Question 10

for a given drug concentration gradient across a membrane, the rate of diffusion increases with the ___ ____ of the drug

Answer 10

lipid solubility

Question 11

what is delta CM

Answer 11

the difference in concentration of a drug in the outer part of the membrane to the innermost part of the membrane

Question 12

why is it important for drugs to be lipid soluble

Answer 12

so that a concentration gradient is set up between the outside and inside of the cell

Question 13

only ____ forms of drugs readily diffuse across the lipid bilayer

Answer 13

unionised

Question 14

acids become more ionised as the pH ______

Answer 14

increases

Question 15

Bases become more ionised as the pH ______

Answer 15

decreases

Question 16

acids ____ protons

Answer 16

donate

Question 17

bases ___ protons

Answer 17

accept

Question 18

the degreee of ionisation depends on the ____ of the drug and the ____ ____

Answer 18

pKa, local pH

Question 19

what is pKa

Answer 19

the pH at which 50% of the drug is ionised and 50% unionised

Question 20

acid = pKa - pH = log (\_\_\_/\_\_\_ ) 
base = pKa - pH = log (\_\_\_/\_\_\_ )

Answer 20

acid= pKa - pH = log (HA/A-) or pH- pKa = log (A-/HA) 
base= pKa - pH = log (BH+/B)

Question 21

absorption of __ ___ is facilitated by the pH of the stomach

Answer 21

weak acids

Question 22

weak acids and bases are ___ absorbed and strong acids and bases are ___ absorbed

Answer 22

well, poorly

Question 23

the rate of absorption of a drug is modified by ___ rich foods as the drug becomes ____ if bound to this

Answer 23

calcium, charged

Question 24

what is oral availability?

Answer 24

the fraction of the drug that reaches the systemic circulation after oral ingestion

Question 25

what is systemic availability?

Answer 25

the fraction of the drug that reaches the systemic circulation after absorption

Question 26

what is first pass or presystemic metabolism

Answer 26

when drugs administered orally, once absorbed are inactivated by enzymes in the gut wall and liver before reaching the systemic circulation and body tissues in general.

Question 27

which administration routes avoid first pass metabolism?

Answer 27

sublingual/buccal transdermal/subcutaneous IV Intramuscular partly rectal and partly not

Question 28

ionised and unionised drugs that are NOT BOUND TO PROTEIN can move freely by _____ between ___ ___ and ___ ___

Answer 28

diffusion, between plasma water and interstitial water

Question 29

____ drugs cannot move between compartments

Answer 29

bound

Question 30

only unionised drugs can move readily by ___ between interstitial water and ___ , ____ ___ and ______ ____

Answer 30

diffusion, between fat, intracellular water and transcellular water