Drug Excretion & Pharmacokinetics Summary - PK6

Question 1

What are the two major processes of drug elimination?

Answer 1

Metabolism & Excretion.

Question 2

What is metabolism in drug elimination?

Answer 2

The conversion of a drug into an inactive form or metabolites.

Question 3

What is excretion in drug elimination?

Answer 3

The irreversible removal of a drug or its metabolites from the body.

Question 4

Can drugs be excreted unchanged?

Answer 4

Yes, some drugs are excreted without metabolism.

Question 5

What is drug clearance?

Answer 5

The efficiency of irreversible elimination of a drug.

Question 6

How is clearance (CL) defined?

Answer 6

The volume of plasma completely cleared of drug per unit time.

Question 7

What is the unit of clearance?

Answer 7

Volume/time (e.g., mL/min, L/hr).

Question 8

What does a high clearance value indicate?

Answer 8

The drug is rapidly eliminated from the body.

Question 9

What does a low clearance value indicate?

Answer 9

The drug is slowly eliminated from the body.

Question 10

What is total body clearance (CL_total)?

Answer 10

The sum of renal clearance, hepatic clearance, and other clearance pathways.

Question 11

What is the formula for total body clearance?

Answer 11

CL_total = CL_renal + CL_hepatic + CL_lung + …

Question 12

What is renal clearance?

Answer 12

The volume of plasma completely cleared of drug per unit time by the kidneys.

Question 13

What factors affect renal clearance?

Answer 13

Urine pH, protein binding, drug solubility, kidney function.

Question 14

How does urine pH affect weak base excretion?

Answer 14

Acidic urine → Increased excretion.

Question 15

How does urine pH affect weak acid excretion?

Answer 15

Alkaline urine → Increased excretion.

Question 16

Example: How does urine pH affect diethylcarbamazine (pKa 10)?

Answer 16

Acidic urine: CL = 38 L/hr (high excretion). Alkaline urine: CL = 1 L/hr (low excretion)

Question 17

What is the elimination rate constant (Kel)?

Answer 17

The rate at which a drug is removed from the body.

Question 18

What is the unit of Kel?

Answer 18

Time⁻¹ (e.g., h⁻¹ or 1/h).

Question 19

How does Kel relate to clearance?

Answer 19

Kel = CL / Vd.

Question 20

What does a high Kel indicate?

Answer 20

The drug is eliminated quickly.

Question 21

What does a low Kel indicate?

Answer 21

The drug is eliminated slowly.

Question 22

What is the definition of drug half-life (t1/2)?

Answer 22

The time required for the plasma concentration of a drug to decrease by 50%.

Question 23

What happens after 1 half-life?

Answer 23

50% of the drug remains in the body.

Question 24

What happens after 2 half-lives?

Answer 24

25% of the drug remains.

Question 25

How many half-lives are required for a drug to be almost fully eliminated?

Answer 25

10 half-lives.

Question 26

What is the formula for half-life?

Answer 26

t1/2 = 0.693 × (Vd / CL).

Question 27

What is the half-life of adrenaline?

Answer 27

2-3 minutes (very short).

Question 28

What is the half-life of lidocaine?

Answer 28

~2 hours.

Question 29

What is the half-life of amiodarone?

Answer 29

Up to 107 days (longest half-life)

Question 30

What factors increase drug half-life?

Answer 30

1. Decreased metabolism (liver disease, enzyme inhibitors). 2. Decreased clearance (renal failure). 3. High plasma protein binding. 4. High tissue binding (high Vd). 5. Enterohepatic circulation.

Question 31

What factors decrease drug half-life?

Answer 31

1. Increased metabolism (enzyme inducers). 2. Increased clearance (alkaline urine for weak acids). 3. Low plasma protein binding. 4. Low tissue binding (low Vd)

Question 32

How does half-life affect dosing frequency?

Answer 32

Short t1/2 → More frequent doses. Long t1/2 → Less frequent doses.

Question 33

How does half-life affect drug accumulation?

Answer 33

Drugs with long half-lives accumulate in the body with repeated dosing.

Question 34

Why is half-life important in overdose management?

Answer 34

Determines how long the drug stays in the body and whether dialysis is effective

Question 35

What is AUC in pharmacokinetics?

Answer 35

The total amount of active drug that reaches systemic circulation.

Question 36

What does AUC represent?

Answer 36

Drug exposure over time.

Question 37

What is the unit of AUC?

Answer 37

Concentration × Time (e.g., mg/L × h).

Question 38

How is AUC calculated?

Answer 38

Using the trapezoidal rule (sum of small trapezoidal areas under the curve).

Question 39

What is the main determinant of drug elimination?

Answer 39

Clearance (CL).

Question 40

How does Vd affect half-life?

Answer 40

Higher Vd → Longer half-life. Lower Vd → Shorter half-life.

Question 41

How does half-life impact steady-state drug levels?

Answer 41

Steady-state is reached after ~5 half-lives.

Question 42

What is the relationship between CL, Vd, and t1/2?

Answer 42

t1/2 = 0.693 × (Vd / CL).

Question 43

How can urine pH be modified for drug excretion?

Answer 43

Sodium bicarbonate (alkaline urine) → Increases weak acid excretion.