Drug Absorption and GI Motility

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Questions and Answers

What is the primary site for drug absorption after oral administration?

Upper small intestine (correct)

Lower small intestine

Stomach

Large intestine

Which anatomical feature of the duodenum enhances drug absorption?

Lymphatic vessels

Smooth muscle layer

Valve-like folds (correct)

Circular folds

What effect does GI motility have on orally administered drugs?

It ensures the drug is absorbed in the stomach

It facilitates the movement of the drug through the alimentary canal (correct)

It slows down absorption by increasing concentration

It stabilizes the drug at the absorption site

During which state is the migrating motor complex (MMC) primarily active?

Interdigestive state Signup and view all the answers

What is the role of the capillary network in the duodenal region?

To maintain a concentration gradient for drug diffusion Signup and view all the answers

What type of contractions replace the MMC during the fed state?

Irregular contractions Signup and view all the answers

How does food presence in the GI tract impact drug absorption?

It causes a delay in reaching the absorption window Signup and view all the answers

What type of drugs must be fully released into the absorption window for effective absorption?

Nonbiodegradable controlled-release dosage forms Signup and view all the answers

What primarily influences the rate of gastric emptying of fatty acids?

The concentration and carbon chain length of fatty acids Signup and view all the answers

Which of the following factors is NOT associated with delayed gastric emptying time?

Drinking warm beverages Signup and view all the answers

What happens to the stability of penicillin if there is a delay in gastric emptying?

It decomposes due to acid instability Signup and view all the answers

Which type of meal is likely to empty the stomach more slowly?

Fatty foods Signup and view all the answers

What is the typical gastric emptying time for liquids compared to solid foods?

Liquids empty faster than digested solids Signup and view all the answers

How does the volume of a meal affect gastric emptying after an initial period?

Larger volume initially empties quickly but slows down later Signup and view all the answers

Which of the following particles is least likely to be retained in the stomach?

Small particles less than 1 mm Signup and view all the answers

Which type of triglycerides is more effective at reducing gastric emptying rate?

Unsaturated triglycerides Signup and view all the answers

What percentage of cardiac output does the splanchnic circulation receive?

28% Signup and view all the answers

How does a decrease in mesenteric blood flow affect drug bioavailability?

It decreases the rate of drug removal. Signup and view all the answers

What is the primary function of the lymphatic circulation in drug absorption?

To absorb drugs through lacteal vessels. Signup and view all the answers

Which of the following is NOT a way food can affect drug bioavailability from an oral drug product?

Increase in hepatic metabolism Signup and view all the answers

What effect does the presence of food have on splanchnic blood flow?

Increases it Signup and view all the answers

Which type of drugs are typically absorbed through the lymphatic system?

Lipophilic drugs Signup and view all the answers

What physiological change does food NOT cause in the gastrointestinal tract?

Decrease in drug permeability Signup and view all the answers

What are chylomicrons primarily responsible for absorbing?

Dietary lipids Signup and view all the answers

What is the primary recommendation by the FDA regarding the study of drug bioavailability?

Use of high-calorie and high-fat meals Signup and view all the answers

Which drug's absorption decreases when consumed with food?

Penicillin Signup and view all the answers

How does food presence in the gastrointestinal (GI) lumen affect drug absorption?

It stimulates gastric acid secretion Signup and view all the answers

What is the effect of a large volume of water on drug bioavailability?

It enhances the solubility and bioavailability of drugs Signup and view all the answers

Why are certain drugs given with food despite a potential reduction in absorption rates?

To avoid irritation of the GI mucosa Signup and view all the answers

What effect does food have on the GI transit time of enteric-coated drugs?

It may prolong GI transit time Signup and view all the answers

Which of the following statements is true regarding antibiotics and GI flora?

Unabsorbed antibiotics can influence the GI flora Signup and view all the answers

What happens to the absorption of basic drugs when gastric acid secretion is reduced?

Absorption is decreased Signup and view all the answers

What effect does co-administration of sodium bicarbonate have on tetracycline absorption?

Reduces absorption by increasing stomach pH Signup and view all the answers

Which meal timing leads to enhanced absorption of ticlopidine?

30 minutes after a fatty meal Signup and view all the answers

What is a common side effect experienced by subjects who fast before taking ticlopidine?

Increased gastrointestinal complaints Signup and view all the answers

What generally causes the double-peak phenomenon in drug absorption?

Presence of food and variability in gastrointestinal function Signup and view all the answers

After administration, which drug also exhibits the double-peak phenomenon apart from cimetidine?

Dipyridamole Signup and view all the answers

How does ranitidine aid in producing a double-peak effect after IV administration?

By being concentrated in the bile and released into the small intestine Signup and view all the answers

What happens during the absorption of highly water-soluble drugs in relation to the stomach?

Dissolution occurs but minimal absorption happens Signup and view all the answers

What benefit might patients experience by taking certain medications with food?

Improved drug tolerance and compliance Signup and view all the answers

Study Notes

Drug Absorption in the GI Tract

The duodenum is the optimal absorption site for most oral drugs due to its large surface area, consisting of folds, villi, and microvilli.
The duodenum is highly perfused, facilitating a concentration gradient for drug diffusion from the lumen into the bloodstream.

Gastrointestinal Motility

Drug movement within the GI tract is influenced by motility, which varies between the digestive (fed) and interdigestive (fasted) states.
The migrating motor complex (MMC) is a propulsive movement that empties the upper GI tract during the fasted state.
The fed state features irregular contractions responsible for mixing intestinal contents and advancing them towards the colon.

Gastric Emptying Time

The stomach is the initial destination of swallowed drugs, and its emptying rate can significantly affect drug absorption.
Delayed gastric emptying can slow down drug absorption, potentially altering both the rate and extent of drug absorption.
Factors impacting gastric emptying include meal composition (high fat, cold beverages), anticholinergic drugs, and the physical characteristics of the drug (liquids empty faster than solids).

Splanchnic Circulation and Lymphatic Absorption

The splanchnic circulation, receiving 28% of cardiac output, plays a vital role in drug absorption.
Mesenteric blood flow influences drug removal from the intestinal tract, and its reduction can decrease bioavailability.
Lymphatic absorption bypasses the first-pass effect of liver metabolism.
Chylomicrons, lipid-containing particles, facilitate the absorption of lipophilic drugs via the lymphatic system.

Food Effects on Gastrointestinal Drug Absorption

Food can alter drug bioavailability by:
- Delaying gastric emptying: Meals high in fat and calories tend to delay gastric emptying.
- Stimulating Bile Flow: Bile acids can enhance the solubility of fat-soluble drugs.
- Altering pH: Food can affect the pH of the GI tract, impacting the solubility of drugs.
- Increasing Splanchnic Blood Flow: Food increases blood flow to the GI tract.
- Influencing Luminal Metabolism: Food can alter the metabolism of drugs within the GI tract.
- Physical/Chemical Interactions: Food components can interact with drugs, changing their absorption.

Double-Peak Phenomenon

Some orally administered drugs, like ranitidine, cimetidine, and dipyridamole, exhibit a double-peak blood concentration curve in fasted patients.
This phenomenon can be caused by variations in:
- Gastric emptying and intestinal flow rates
- Enterohepatic recycling: Drug reabsorption from the bile.
- Tablet dosage form
This phenomenon might be due to the initial drug release from the stomach and subsequent absorption, followed by a second absorption peak when the remaining dose reaches the duodenum.
Ranitidine exhibits a double-peak after both oral and IV administration.
- Enterohepatic recycling appears to contribute to this phenomenon, as ranitidine is concentrated in the bile and reabsorbed after stimulation by food.

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Description

This quiz covers essential concepts related to drug absorption in the gastrointestinal tract, focusing on the role of the duodenum and factors influencing motility. It also explores the impact of gastric emptying time on drug absorption. Test your knowledge on these critical pharmacological principles.