Ch9 DRUG EXCRETION

Question 1

Drug excretion

Answer 1

the elimination of drugs or drug metabolites from the body. Drugs can be excreted via breath, urine, saliva, perspiration, feces, milk, skin, and hair, but the kidneys are the most important organs involved in elimination of water-soluble drugs and drug metabolites, while the liver is critical for the excretion of less water-soluble drugs in the bile.

Question 2

Excretion by the Kidneys - 3 stages?

Answer 2

The kidneys have three means of interacting with drugs: glomerular filtration, tubular secretion, and tubular reabsorption.

The kidneys filter up to 25% of cardiac output in adults

The normal newborn’s kidney filters 4% to 6% of cardiac output

Question 3

glomerular filtration rate

Answer 3

is a measure of the amount of this filtrate produced. The clearance rate of many drugs varies directly with the glomerular filtration rate because the drugs enter the filtrate but are never reabsorbed. Note that not all drugs are dissolved in the blood; rather, some are bound to proteins such as albumin and thus cannot enter the filtrate

Changes in the filtration rate may dramatically alter the half life of many drugs

The GFR in pregnant women increases 40% to 65% because of increased blood volume and hormonal changes

Question 4

what does hypertension do to the GFR in pregnancy?

Answer 4

it lowers the GFR allowing some drugs reliant on the kidney for clearance a longer half life

Question 5

Tubular Secretion

Answer 5

occurs when solutes are moved out of the peritubular capillaries and into the filtrate in the renal tubule. This is an active process that requires a specific carrier protein. Like all carrier systems, the renal active transport system can be saturated, and therefore the amount of tubular secretion is finite

Question 6

Tubular Reabsorption

Answer 6

normally a passive process whereby solutes follow a concentration gradient back to the capillaries. It can also be an active process in which case adenosine triphosphate is needed to transport solutes against their concentration gradient

Question 7

What can proteinuria indicate?

Answer 7

kidney filtration is not functioning well. May indicate the onset of hypertension. Drugs may build up in circulation

Question 8

Excretion by the Liver

Answer 8

the liver makes drugs more water soluble and therefore more easily excreted via bile and urine; this is critical for lipophilic substances such as many drugs and drug metabolite.