Factors Affecting Absorption -PK2

Question 1

What are the two key parameters of drug absorption?

Answer 1

1. Rate of absorption (related to Tmax) 2. Extent of absorption (related to Cmax).

Question 2

What factors influence drug absorption?

Answer 2

1. Physiochemical properties of the drug 2. Drug formulation 3. Physiological parameters (pH, vascularization) 4. GI tract physiology 5. Pathophysiological conditions

Question 3

What is the pH partition theory?

Answer 3

The degree of drug ionization affects absorption – only unionized drugs cross membranes easily.

Question 4

How does pH affect drug absorption?

Answer 4

Weak acids absorb better in acidic environments (stomach); weak bases in alkaline environments (intestine).

Question 5

What equation determines the ratio of ionized to unionized drug?

Answer 5

Henderson-Hasselbalch equation.

Question 6

What happens when pH = pKa?

Answer 6

50% of the drug is ionized, 50% is unionized.

Question 7

What happens when pH < pKa?

Answer 7

For weak acids: More unionized → Higher absorption.

Question 8

What happens when pH > pKa?

Answer 8

For weak bases: More unionized → Higher absorption.

Question 9

How does pH vary across the GI tract?

Answer 9

• Stomach: 1.5–2.0 (acidic) - Duodenum: 6.1 - Small intestine: 7.1-7.5 - Large intestine: ~7.

Question 10

Why are weak acids absorbed in the stomach?

Answer 10

Because they are mostly unionized in acidic pH, allowing diffusion across membranes.

Question 11

Why are weak bases absorbed in the intestine?

Answer 11

Because they are mostly unionized in alkaline pH, allowing better membrane permeability.

Question 12

Give an example of a weak acid and its absorption pattern.

Answer 12

Salicylic acid (pKa = 3.5): Stomach pH 1.5 → 99% unionized → High absorption.

Question 13

Give an example of a weak base and its absorption pattern.

Answer 13

Metformin (weak base): Fully ionized in intestine, but still absorbed due to active transport mechanisms.

Question 14

What are the limitations of the pH partition theory?

Answer 14

1. Intestinal surface area is larger than the stomach. 2. Membrane permeability is higher in intestines. 3. Active transport mechanisms exist.

Question 15

How does ion-pairing affect drug absorption?

Answer 15

Oppositely charged ions form a neutral complex, improving membrane permeability.

Question 16

What is an example of a drug using active transport?

Answer 16

Melphalan (anti-cancer drug) is absorbed via the phenylalanine transporter.

Question 17

What is the LADME process?

Answer 17

Liberation, Absorption, Distribution, Metabolism, Excretion.

Question 18

What is the difference between disintegration and dissolution?

Answer 18

• Disintegration: Breaking tablets into small particles. - Dissolution: Drug dissolving into solution.

Question 19

How do different formulations affect absorption speed?

Answer 19

(Fastest to slowest): Solution > Suspension > Soft Gel Capsule > Tablet.

Question 20

Why do solutions absorb faster than suspensions?

Answer 20

Suspensions contain solid particles that must dissolve before absorption.

Question 21

How does an enteric coating affect absorption?

Answer 21

Prevents dissolution in the stomach, delays absorption until the intestine

Question 22

What is an Immediate Release (IR) formulation?

Answer 22

Drug is rapidly released into systemic circulation.

Question 23

What is a Modified Release (MR) formulation?

Answer 23

Drug release is controlled over time or in a specific region.

Question 24

What are two types of MR formulations?

Answer 24

1. Delayed Release (enteric coating) 2. Extended Release (slow release over time).

Question 25

What are excipients?

Answer 25

Non-active ingredients added to formulations for functional properties.

Question 26

How do suspending agents affect absorption?

Answer 26

Increase viscosity → Decrease dissolution → Slower absorption.

Question 27

How do surfactants affect absorption?

Answer 27

Low concentration: Increases dissolution. High concentration: Forms micelles, reducing dissolution.

Question 28

How do absorption enhancers work?

Answer 28

Increase membrane permeability for better drug uptake.

Question 29

Why does salt form improve absorption?

Answer 29

Salts dissolve faster than their parent compounds (e.g., Ibuprofen lysine dissolves faster than ibuprofen).

Question 30

How does particle size affect drug absorption?

Answer 30

Smaller particles → Larger surface area → Faster dissolution and absorption.

Question 31

How do crystal forms affect absorption?

Answer 31

Amorphous forms dissolve faster than crystalline forms.

Question 32

How does water hydration affect dissolution?

Answer 32

Hydrated drugs dissolve slower than anhydrous forms.

Question 33

How does blood flow affect drug absorption?

Answer 33

Higher perfusion → Faster absorption.

Question 34

What areas have high tissue perfusion?

Answer 34

Muscle, lungs, nasal cavity, mouth, skin, GI tract, rectum.

Question 35

How does gastric emptying affect drug absorption?

Answer 35

Faster gastric emptying → Faster drug absorption.

Question 36

What factors delay gastric emptying?

Answer 36

1. High-fat meals 2. Large meal volume 3. Cold food 4. Emotional stress 5. Certain drugs

Question 37

How does diarrhea affect drug absorption?

Answer 37

Increased motility → Less residence time → Poor absorption.

Question 38

How does GI resection (e.g., obesity surgery) affect drug absorption?

Answer 38

Reduced surface area → Reduced absorption.

Question 39

How does cardiovascular disease affect absorption?

Answer 39

Reduced blood flow → Lower absorption.

Question 40

How does liver disease affect absorption?

Answer 40

Affects drugs that undergo first-pass metabolism (e.g., propranolol).

Question 41

What is the fastest route of drug absorption?

Answer 41

Intravenous (IV).

Question 42

What is the slowest oral drug formulation for absorption?

Answer 42

Tablets.

Question 43

Why are drugs often recommended on an empty stomach?

Answer 43

To prevent food interactions and ensure rapid absorption.

Question 44

How does high-fat food affect drug absorption?

Answer 44

Delays gastric emptying → Slows absorption