Excretion - PK5

Question 1

What are the two main processes involved in drug elimination?

Answer 1

Metabolism + Excretion

Question 2

What is drug excretion?

Answer 2

The irreversible transfer of drugs/metabolites from the internal environment (body) to the external environment.

Question 3

Why is drug excretion important?

Answer 3

It terminates pharmacological action and prevents toxicity.

Question 4

What are the major routes of drug excretion?

Answer 4

1. Renal (Kidneys – Urinary system) 2. Non-Renal (Biliary, GI, Pulmonary, Skin, Saliva, Mammary, Genital).

Question 5

Which route is responsible for 25-30% of drug elimination?

Answer 5

Renal excretion (Urinary system).

Question 6

What types of drugs are primarily excreted by the kidneys?

Answer 6

Water-soluble (hydrophilic) and low molecular weight drugs (<500 Da).

Question 7

How are lipophilic drugs excreted?

Answer 7

Metabolized in the liver to more water-soluble metabolites, then excreted via kidneys.

Question 8

What are the three main stages of renal excretion?

Answer 8

1. Glomerular Filtration (F) 2. Tubular Secretion (S) 3. Reabsorption (R).

Question 9

How is the total drug eliminated in urine calculated?

Answer 9

Total renal excretion = Filtration + Secretion - Reabsorption.

Question 10

What is glomerular filtration?

Answer 10

Passive filtration of small molecules (<500 Da) into the renal tubule.

Question 11

What factors affect glomerular filtration?

Answer 11

1. Molecular weight (<500 Da filtered easily). 2. Protein binding (only free drugs pass).

Question 12

What is tubular secretion?

Answer 12

Active transport of drugs from blood → renal tubule (requires energy).

Question 13

Which transporters are involved in tubular secretion?

Answer 13

OAT (Organic Anion Transporter) for acidic drugs & OCT (Organic Cation Transporter) for basic drugs.

Question 14

What is tubular reabsorption?

Answer 14

Movement of drugs from renal tubule back into blood (depends on lipid solubility & ionization).

Question 15

How does urine pH affect drug excretion?

Answer 15

It affects ionization, influencing whether a drug is reabsorbed or excreted.

Question 16

What is the pH partition theory?

Answer 16

Ionized drugs are poorly reabsorbed and excreted more easily.

Question 17

How does urine pH influence weak acids?

Answer 17

Basic urine → ionized acid (A-) → more excretion.

Question 18

How does urine pH influence weak bases?

Answer 18

Acidic urine → ionized base (BH⁺) → more excretion.

Question 19

Give a clinical example of urine pH manipulation.

Answer 19

Aspirin overdose (weak acid, pKa = 3.5) → treated with urinary alkalinization (e.g., bicarbonate) to increase excretion.

Question 20

What factors can affect renal drug excretion?

Answer 20

1. Plasma protein binding 2. Urine pH 3. Drug competition at transporters 4. Renal function 5. Age & Sex.

Question 21

How does plasma protein binding affect excretion?

Answer 21

High protein binding → less filtration → reduced excretion.

Question 22

How does renal function affect excretion?

Answer 22

Poor renal function → reduced drug elimination → dose adjustment needed.

Question 23

How does sex & age affect renal excretion?

Answer 23

Females excrete 10% less than males. Elderly & infants have lower renal function, requiring dose adjustments.

Question 24

What are the main non-renal excretion routes?

Answer 24

1. Biliary (Liver & Intestine) 2. Gastrointestinal (Feces) 3. Pulmonary (Lungs) 4. Skin (Sweat) 5. Salivary 6. Mammary (Breast Milk).

Question 25

How does the biliary system contribute to excretion?

Answer 25

Drugs/metabolites are secreted into bile, enter the intestine, and can be excreted in feces.

Question 26

What molecular weight drugs are excreted in bile?

Answer 26

>500 Da → Biliary excretion <300 Da → Renal excretion 300-500 Da → Both routes.

Question 27

What is enterohepatic circulation?

Answer 27

Drug is excreted in bile, hydrolyzed in intestine, reabsorbed, and recirculated (prolongs drug action).

Question 28

What is an example of enterohepatic circulation?

Answer 28

Leflunomide (rheumatoid arthritis drug) → remains in blood for >2 weeks, requiring activated charcoal for washout.

Question 29

What is pulmonary excretion?

Answer 29

Excretion via lungs (important for volatile drugs like anesthetics & alcohol).

Question 30

Give an example of a drug excreted via lungs.

Answer 30

Halothane (anesthetic gas) & alcohol (breath test detection).

Question 31

What is gastrointestinal excretion?

Answer 31

Drugs excreted in feces (unabsorbed drugs or those secreted into bile).

Question 32

What drugs are excreted in feces?

Answer 32

Nicotine, quinine, corticosteroids, streptomycin.

Question 33

What is mammary excretion?

Answer 33

Drugs excreted into breast milk (lipophilic, unionized drugs).

Question 34

Why can weak bases accumulate in breast milk?

Answer 34

Milk is slightly acidic (pH 6.4-7.6), so basic drugs ionize and get trapped.

Question 35

What drugs are excreted in saliva?

Answer 35

Caffeine, phenytoin, theophylline (causing a bitter taste).

Question 36

How does skin excrete drugs?

Answer 36

Through sweat, hair follicles, and keratin (e.g., arsenic, mercury, ethanol, amphetamines).

Question 37

What is the formula for total renal excretion?

Answer 37

F (filtration) + S (secretion) - R (reabsorption).

Question 38

How can drug excretion be enhanced?

Answer 38

By manipulating urine pH (acidic urine → basic drugs excreted, basic urine → acidic drugs excreted).

Question 39

How does enterohepatic circulation affect drug half-life?

Answer 39

It prolongs drug action by recirculating drugs.

Question 40

Why must drug dosing be adjusted in renal disease?

Answer 40

Reduced renal clearance → risk of drug accumulation and toxicity.