excretion

Question 1

some of the molecules that are released into the bile are..

Answer 1

absorbed again in the small intestine and returned to the liver

Question 2

what are the molecules that are absorbed in the small intestine and liver part of?

Answer 2

enterohepatic circulation

Question 3

transfer of drug or drug metabolites from the plasma to the bile through the hepatocytes (biliary excretion) is…

Answer 3

irreversible

Question 4

transfer of drug or drug metabolites from the plasma to the bile through the hepatocytes (biliary excretion) is followed by

Answer 4

intestinal reabsorption of the active drug (enterohepatic cycle).

Question 5

how can active drug be regenerated after it has been through phase one and 2

Answer 5

Concentrated in bile and given back into intestines – into interstines and hydrolysed - be deivered back into the circulatory system – known as enterohepatic circulation

Question 6

Excretion

Answer 6

Combination of mechanisms by which a drug is irreversibly transferred from the systemic circulation into extracorporal fluids (e.g. urine or bile).”

Question 7

how are the majority of drugs removed form the body?

Answer 7

renal excretion in the urine

Question 8

clearance is

Answer 8

the volume of plasma from which a substance is completely removed in a given amount of time.

For example, the clearance for urea is 65 ml/min. This means that the all of the urea in 65 ml of plasma is removed in one minute.

Question 9

what is the maximum renal clearance

Answer 9

700ml/min, which is the renal blood flow

Question 10

what are some other routes of elimination?

Answer 10

saliva, sweat, tears faeces (especially in renal impairment) and lungs (e.g. volatile anaesthetics)

Question 11

what sort of compounds would concentrate in breast milk?

Answer 11

basic compounds because breast milk is more acidic than blood plasma

Question 12

renal clearance equation

Answer 12

Clren = (Cu x Vu) / Cp

Question 13

what are the 3 fundamental processes which account for renal drug excretion?

Answer 13

• glomerular filtration
• active tubular secretion
• passive reabsorption (diffusion from the concentrated tubular fluid back across tubular epithelium).

Question 14

why should you consider renal function when dosing a drug?

Answer 14

• work out whether the drug will accumilate in body or all be excreted
  Varies massively per drug

Question 15

if a drug was going to reabsorbed in the kidney where would this be?

Answer 15

proximal convoluted tubule

Question 16

how are the drugs eliminated in the urine

Answer 16

as whole or metabolites

Question 17

how much plasma(blood) is filtered through the glomerulus?

Answer 17

20%

Question 18

what would secrete drugs into the tubules for excretion?

Answer 18

peritubular capilaries

Question 19

what is the difference in glomeruli filtration and peritubular elimination?

Answer 19

glomerulus will only remove free drug, where as peritubular will also remove protein bound drug (polarity and ionised would affect whether bound or not)

Question 20

how would penicillin be removed from the plasma

Answer 20

completely through peritubular secretion

Question 21

how does most peritubular secretion occur?

Answer 21

via OAT (organic anion transporter) or OCT (organic cation transporter). These use co-transportation of ions into/out of cell.

Question 22

what size of molecule will the glomerulus allow to cross

Answer 22

20 kilo dalton

albumin - 68kD

Question 23

how much drug excretion goes through organic anionic and cationic transporters?

Answer 23

80%

Question 24

why are OAT and OCTs important

Answer 24

removing drugs that are bound to plasma proteins and drugs that are too large in molecular weight to remove through glomerulus

Question 25

what is the range of pH in urine?

Answer 25

4.5-8

pH is lower in the morning than in the evening

Question 26

if you overdosed on a weak acidic drug what would happen to the urine/

Answer 26

would make the urine more alkali – from pKa the drug wont be ionised will stay in compartment and be excreted

Question 27

if you overdosed on a basic drug what would happen to the urine/

Answer 27

make the urine more acidic – from pKa the drug wont be ionised will stay in compartment and be excreted

Question 28

is it more common for drugs to be excreted through the kidney unchanged or as metabolites

Answer 28

as metabolites

Question 29

how do free drugs pass into the glomeruli filtrate

Answer 29

freely

20% of renal plasma flow

Question 30

how are 80% or weak acid/basic drugs secreted into the renal tubule for excretion?

Answer 30

actively through peritubular capilaries

Question 31

how are lipid soluble drugs (uncharged) reabsorbed

Answer 31

by diffusion drag in the renal tubules

Question 32

what happens to charged molecules in the urine

Answer 32

they are trapped and held back

Question 33

Absorption

Answer 33

Speed, route, bioavailability, effect of GI pH

Question 34

Distribution

Answer 34

Final equilibrium volumes of distribution
Equilibration in/out of ‘compartments’ with differing speeds
Plasma protein binding

Question 35

Metabolism

Answer 35

First order, zero order, saturating first order

Individual/ethnic differences in CYP450

Question 36

Excretion

Answer 36

Entero-hepatic circulation

pH of urine