Biopharmaceutics Part A

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Questions and Answers

What is the approximate length of the human small intestine?

10 meters

4-5 meters (correct)

6 meters

1.5 meters

What is the primary role of the stomach in drug absorption?

Breakdown of food into chyme (correct)

Production of enzymes for digestion

Storage and compaction of feces

Absorption of most drugs

What is the typical pH range of the small intestine?

1-2

7-8

4-5

6-7 (correct)

What is the primary function of villi in the small intestine?

Increase surface area for absorption Signup and view all the answers

What is the approximate ratio of surface area between the stomach and the small intestine?

1:3800 Signup and view all the answers

Which of the following is NOT transported by the paracellular pathway?

Proteins Signup and view all the answers

Which of the following statements about the paracellular pathway is TRUE?

Absorptive epithelia are generally more permeable to the paracellular pathway than other epithelia. Signup and view all the answers

Which of the following factors can INFLUENCE the bioavailability of a drug?

All of the above Signup and view all the answers

What is the MAXIMUM molecular weight of a drug that can be efficiently transported by the paracellular pathway?

200 Da Signup and view all the answers

How does the presence of food in the GI tract affect drug absorption?

Food can either increase or decrease drug absorption, depending on the drug and the food. Signup and view all the answers

Which of these best describes the movement of molecules in active transport?

Molecules move from low to high concentration Signup and view all the answers

What is a defining characteristic of carrier-mediated transport?

Requires energy input Signup and view all the answers

Which of these are NOT transported via active transport? (Select all that apply)

Oxygen Signup and view all the answers

Which of the following is a key difference between active and facilitated diffusion?

Active transport moves molecules against a concentration gradient, while facilitated diffusion does not. Signup and view all the answers

Which transport mechanism(s) require(s) a concentration gradient for driving force?

Passive diffusion and facilitated diffusion Signup and view all the answers

What is the primary function of active transport in drug absorption?

To move drugs from areas of low concentration to areas of high concentration. Signup and view all the answers

Which of the following statements about active transport is TRUE?

Active transport is a vital mechanism for the absorption of nutrients, vitamins, and some drugs. Signup and view all the answers

Which type of endocytosis is considered non-specific and low efficiency?

Pinocytosis Signup and view all the answers

What is the relationship between gastric emptying time and the nature of the dosage form?

Gastric emptying time is highly variable depending on the dosage form. Signup and view all the answers

How does the fed state affect gastric emptying?

It enhances retropulsion in the stomach. Signup and view all the answers

What dosage form is expected to remain in the fed stomach longer?

Extended release dosage forms Signup and view all the answers

What is the primary goal of the migrating myoelectric complex (MMC)?

To clear undigested material from the gastrointestinal tract. Signup and view all the answers

In what manner should drugs be taken to reach the intestine quickly?

Without food and/or water Signup and view all the answers

Which of the following drugs is typically administered via enteric-coated tablets to influence absorption?

Both erythromycin and omeprazole Signup and view all the answers

How long does small intestinal transit typically take?

3 to 4 hours Signup and view all the answers

Which physiological factor does NOT influence the absorption of drugs in the gastrointestinal tract?

Body temperature Signup and view all the answers

Which of the following is NOT a factor that influences the rate of passive diffusion?

Presence or absence of food in the GI tract Signup and view all the answers

Which of the following statements accurately describes the significance of the gastrointestinal membrane in drug absorption?

It acts as a barrier to drug absorption, controlling the rate at which drugs enter the bloodstream. Signup and view all the answers

Which type of transport mechanism is primarily responsible for the absorption of the majority of drugs across the gastrointestinal membrane?

Passive diffusion Signup and view all the answers

In the equation `dC/dt = k(Cg-Cb)`, what does `Cb` represent?

The concentration of the drug in the blood Signup and view all the answers

Which of the following is a characteristic of passive diffusion?

It is influenced by the drug's lipid solubility. Signup and view all the answers

What form of a weak electrolyte drug is generally more readily absorbed via passive diffusion?

The unionized form Signup and view all the answers

Which of the following drugs is mentioned in the text as being affected by food-induced changes in presystemic metabolism?

Ciclosporin Signup and view all the answers

Which of the following statements is TRUE regarding the environment within the lumen of the gastrointestinal tract?

Local diseases and physiological disorders can influence drug absorption in the GI tract. Signup and view all the answers

What role does mucus play in the gastrointestinal epithelium?

It acts as a protective barrier and aids in lubrication. Signup and view all the answers

What effect does the pyloric sphincter have on gastric residence time?

It controls the passage of stomach contents into the small intestine. Signup and view all the answers

Which factor can greatly influence the rate of passive diffusion in drug absorption?

The concentration of the drug in gastric fluids. Signup and view all the answers

Under what conditions are 'sink conditions' maintained during drug absorption?

When the concentration of the drug in the blood is much less than in the GI fluids. Signup and view all the answers

What describes the absorption of small lipophilic molecules in the GI tract?

They primarily utilize passive diffusion. Signup and view all the answers

Which statement is true about active transport mechanisms in the GI membrane?

They can operate against a concentration gradient using energy. Signup and view all the answers

What is the primary impact of food and gastrointestinal pH on drug absorption?

They can either increase or decrease the bioavailability of certain drugs. Signup and view all the answers

Which mechanism is primarily responsible for drug absorption across the gastrointestinal membrane?

Passive diffusion. Signup and view all the answers

Study Notes

Aulton chapter 19, 20
Topics covered include GI tract physiology, drug absorption, pharmaceutical transit, GI barriers, and drug transport mechanisms.
Oral route is the most common drug administration method.

Objectives

Students should understand the GI tract physiology for drug absorption.
Students should understand the transit of pharmaceuticals in the GI tract.
Students should understand barriers to drug absorption in the GI tract.
Students should know GI membrane structures and drug transport mechanisms.

GI Tract - Physiology and Drug Absorption

GI Tract is 6 meters long and has four main segments: esophagus, stomach, small intestine, and large intestine.
Mucous lining covers the GI epithelium and acts as a viscoelastic aqueous gel, composed of large glycoproteins called mucins. The average thickness is 80 µm (ranging from 5 to 500 µm).

Stomach

Stomach's volume under fasting conditions.
Chyme is the uniform creamy consistency in the stomach.
Absorption? (Question, with no definite answer in provided information)
Stomach pH and secretions: acid, gastrin, pepsin, and mucus.
The pyloric sphincter is crucial in regulating stomach emptying.

Small Intestine

Length is 4-5 meters.
pH? (Question, with no specific pH value).
Villi are finger-like projections into the lumen, roughly 0.5-1.5 mm in length and 0.1 mm in diameter. Each villus has 600-1000 microvilli.
Roles of the small intestine: major site of nutrient absorption.
Duodenum, jejunum, and ileum are the sections of the small intestine, relevant for absorption.
Ratio of stomach to small intestine surface area is 1 to 3800.

Colon

Length is approximately 1.5 meters.
Roles of the colon: absorption of sodium ions, chloride ions, and water; storage and compaction of feces; presence of bacteria.
Colon is colonized by bacteria. The bacteria in the colon can affect certain medications.

Transit of Pharmaceuticals in GI Tract

Gastric emptying time is equal to gastric residence time, which is highly variable, and is dependent on the nature of the dosage form and the fed/fasting state.
The presence of food can significantly impact the transit time of pharmaceuticals.

Interdigestive Myoelectric Cycle

Also known as the migrating myoelectric complex (MMC).
Occurs in the fasting state.
Describes the stages of the myoelectric cycle (e.g. phases I-III).
MMC plays a role in removing undigested food and preventing bacterial overgrowth.

Fed State

Peristalsis—contraction of the distal stomach
Mixes and breaks down food and moves towards pyloric sphincter.
Emptying and retropulsing into the stomach's antrum (The action of retropulsing)
Which dosage form stays in the stomach for longer if fed? Extended release dosage forms are the answer.

Gastric Emptying of Drugs

For rapid intestinal drug delivery, dosage form should be taken without food and/or water.

Small Intestinal and Colonic Transit

Small intestinal transit is relatively constant, at around 3-4 hours.
Colonic transit can range from 2-48 hours.

Barriers to Drug Absorption

Barriers to drug absorption in the GI tract include unstirred water layer, presystemic metabolism, chemical degradation, enzymatic degradation, complexation to mucus, adsorption, water and mucus diffusion, and efflux.
Gastrointestinal pH.

Environment within the Lumen

GI pH can influence drug absorption (enteric coated tablets can be used to target pH).
Importance of drugs with examples.
GI lumen enzymes may affect drugs, with example of sulfasalazine.
Food components (food-drug interactions) can affect drug absorption, with example of tetracycline.
Disease state and physiological disorders (e.g., local diseases, gastric surgery) can alter drug absorption.

GI Membrane and Mechanisms of Drug Transport

GI membrane is the major cellular barrier to drug absorption and is semi-permeable.

Mechanisms of Drug Transport Across the Membrane

Several transport mechanisms exist: Paracellular (between cells), Transcellular (across cells), Passive diffusion, carrier mediated transport (active transport, facilitated diffusion), and Endocytosis (pinocytosis and phagocytosis).

Passive Diffusion

Drugs move from higher to lower concentration across GI membrane.
Rate of transport depends on physicochemical properties of the drug, nature of the membrane, and concentration gradient.
Factors like the diffusion coefficient, surface area, and membrane thickness affect the rate.

Carrier-mediated Transport: Active Transport

Energy-dependent process.
Transport can occur against concentration gradients.
Transporters show specificity towards particular compounds (e.g., nutrients, amino acids, sugars, electrolytes, vitamins B1, B2, B12, bile salts); these transporters are vital for absorption.

Carrier-mediated Transport: Facilitated Diffusion

No energy input.
Similar to active transport, shows dependence on specific chemical structures.
Plays a minor role in drug absorption.

Review Questions

Small intestine's material transit is relatively constant.
Food's presence might increase or reduce drug absorption.
The transit of materials through the small intestine is relatively constant.

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Description

This quiz focuses on the gastrointestinal tract's physiology and its essential role in drug absorption. Key topics include the anatomy of the GI tract, drug transport mechanisms, and barriers to absorption. Understanding these principles is crucial for mastering pharmaceutical studies.

Biopharmaceutics Part A - Aulton Chapters 19, 20

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