Pharmacokinetics

Question 1

Define Excretion

Answer 1

Excretion is inactive drug or metabolites leaving the body.

Question 2

T/F drugs can be eliminated from the body unchanged.

Answer 2

T

Question 3

Renal excretion consists of 3 mechanisms:

Answer 3

Passive Glomerular Filtration, Partial Resorption, Active Tubular secretion.

Question 4

Through what process does glomerular filtration occur?

Answer 4

Passive diffusion, The drug most be lipid-soluble enough to be filtered by the glomeruli.

Question 5

Explain the process of Partial Reabsorption.

Answer 5

Lipid-soluble drugs will cross the renal tube and re-enter blood circulation. Polar (water soluble) drugs remain in the urine.

Question 6

Explain the concept of Active Tubular Secretion

Answer 6

Drugs are moved into the urine via facilitated proteins against the concentration gradient

Question 7

What is the purpose of Creatinine Clearance ?

Answer 7

Creatinine is a waste product of muscle wear and tear. It is removed from the body only by renal excretion. As a result, it is used a way to determine nephron function, how well your kidneys are working.

Question 8

What is the normal range for Creatinine clearance?

Answer 8

80-100 ml/min. Anything below this will indicate poor glomerular filtration. Over 100mL/min indicates great kidney function.

Question 9

The rate of excretion depends on ?

Answer 9

The relationship between albumin bound drugs and free drugs, blood flow, glomerular filtration rate.

Question 10

What are some limitations of Creatinine Clearance?

Answer 10

Serum creatinine is assumed at steady state (will always be the same), Creatinine level lag behind renal function by 1-2 days, Muscle trauma (higher Creatinine levels), less muscle mass ( but mid range normal= not good renal function)

Question 11

What is the role of cystatin C?

Answer 11

Cystatin C is a protein, it is being explored as a Novel way to determine kideny function. Found in all tissues. Might be a more accurate predictor of renal function.

Question 12

Explain why weak acids are excreted readily in basic urine and slowly in acidic urine.

Answer 12

Weak acid become water soluble in basic urine but lipid soluble in acidic urine.

Question 13

What is hemodialysis?

Answer 13

It is an artificial kidney helpful in treating drug overdoses thats inserum.

Question 14

What are other means of drug excretion?

Answer 14

Biliary excretion, Lung excretion, Sweat, saliva, Mammary Glands

Question 15

What is the process of Biliary Excretion?

Answer 15

After liver metabolism- metabolites move from bile to the duodenum for fecal excretion.

Question 16

What are factors that affect drug excretion by lung?

Answer 16

Rate and depth of respiration and cardiac output. Respiratory compromise and decreased cardiac output can prolong elimination of drug.

Question 17

Explain why some drug can get trapped in breast milk?

Answer 17

The breast milk is acidic and drugs can get trapped by ion trapping. Basic drugs can get ionized

Question 18

What is the distinction between pharmacokinetics and pharmacodynamics?

Answer 18

Pharmacodynamics is how drugs affect the body. Pharmacokinetics is what the body does to drug.

Question 19

What is first order elimination?

Answer 19

1st order elimination is concentration dependent and it is the rate at which drugs leave the body. (half-life elimination).

Question 20

Define half-life.

Answer 20

The time required for half the drug to leave the body when drug equilibrium is achieved. The time it takes to remove half the drug from the body.

Question 21

When is a drug consider to be gone from the body?

Answer 21

When 5 half-lives has passed.

Question 22

What is the difference between alpha 1/2 life and beta 1/2 life?

Answer 22

Alpha 1/2 life is the time it takes the drug to be distributed throughout the body. Beta 1/2 life is the elimination of the drug. The time it takes for half the drug to leave the body.

Question 23

Ampicillin has a half life of 2 hours while diazepam has a half life of 48 hours. Which drug will require more redose to maintain it’s therapeutic effect?

Answer 23

Ampicillin

Question 24

Explain what it mean for 1st order elimination not to be dose dependent.

Answer 24

Regardless of the dose administered of a drug the half-life will always be the same. For example the half-life of ampicillin is 2 hours. If 20 mg of ampicillin is Iv administered, in 2 hours 10mg will remain. Of if 50 mg of ampicillin is Iv administered, 25 mg remain in 2 hours.

Question 25

How is zero order elimination different from 1st order elmination?

Answer 25

1st order elimination is concentration dependent and it is elimination by half-life elimination. While zero order elimination in not concentration dependent and elimination occurs every hour. zero order elimination is seen when the system in saturation by a drug. Once enough drug has been removed and the body is no longer saturated, 1st order elimination may occur.

Question 26

define steady state.

Answer 26

With repeated dosing, the rate of input= rate of output. (the rate of administered drug will = the rate of excretion). This will only work for 1st order elimination.

Question 27

How many half-life dose it take to reach steady state?

Answer 27

4-5 half-lives.

Question 28

What is the purpose of combining loading dose with maintenance dose?

Answer 28

Load dose is the administration of a larger dose of drug to achieve the desired therapeutic effect at the receptor. However, once that effect has been achieved it will not be maintained with that one dose. By adding the maintenance dose we are able to maintained the therapeutic effect. Steady state will not be achieved until 5 half-lives..

Question 29

What is trough and peak? And at which phase would it be best to draw blood?

Answer 29

Trough is the point at which the drug is low in the blood and peak is the point at which the drug is high in the blood. It would be best to draw blood during the trough, indicate when its time to redose.

Question 30

Patient factors that influence the action of drug. Please provide examples.

Answer 30

Age: the liver of an old vs young person determines the body’s ability to metabolise drugs via liver. drugs.
body mass: some drugs are given based on body mass. (large body, less concentration of drug will enter systemic circulation and vice versa)
gender: the size of male vs women
pathological state: nausea vomiting, diarrhea, renal dysfunction
psychological factors: Placebo- pt believes med will work they feel better.
Genetics: inherited enzyme deficiencies