Pharmacology Absorption and Routes of Administration

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Questions and Answers

What is the primary effect of increasing the surface area of a drug formulation on oral absorption?

It enhances dissolution and absorption. (correct)

It slows down the absorption rate.

It decreases the bioavailability.

It increases the molecular weight of the drug.

How does the thickness of the diffusion layer impact drug absorption?

Thickness of the diffusion layer has no effect on absorption.

Thicker diffusion layers always increase the absorption rate.

Thinner diffusion layers decrease the residence time.

Thicker diffusion layers can slow down absorption. (correct)

Which alteration of drug formulation is least likely to help extend the drug release for prolonged exposure?

Increase thickness of diffusion layer.

Use extended-release tablets.

Decrease surface area.

Decrease thickness of diffusion layer. (correct)

What is a significant advantage of smaller sized drugs when it comes to oral absorption?

They can pass through epithelial cells more easily. Signup and view all the answers

Which combination of factors would most likely reduce the oral absorption of a drug?

Increasing particle size and thickness of diffusion layer. Signup and view all the answers

What is the primary movement defined in the context of absorption?

Movement of drug from site of administration to the bloodstream Signup and view all the answers

Which of the following routes of administration require absorption?

Intranasal Signup and view all the answers

Which major site of absorption for oral administration is emphasized?

Small intestine Signup and view all the answers

What is one of the advantages of oral drug administration?

Can be administered in outpatient settings Signup and view all the answers

What is a disadvantage of oral drug administration?

It can be inefficient due to multiple barriers Signup and view all the answers

Which of the following factors does NOT affect oral drug absorption?

Economic factors Signup and view all the answers

Which method of drug administration avoids the absorption phase altogether?

Intravenous Signup and view all the answers

Why is the concentration gradient important in drug absorption?

It encourages the movement of the drug into the bloodstream Signup and view all the answers

Which of the following is classified as a parenteral route of administration?

Intramuscular Signup and view all the answers

What distinguishes enteral administration from parenteral administration?

Enteral administration occurs inside the gastrointestinal tract Signup and view all the answers

Study Notes

Absorption

Absorption is the movement of a drug from the site of administration to the bloodstream.
Sites of administration differ and influence the absorption barriers.
The concentration gradient between the blood and site of administration encourages absorption.

Learning Objectives

Identify routes of administration requiring absorption.
Define advantages and disadvantages of oral administration.
Understand and describe the major physiological factors affecting oral drug absorption.
Understand and describe the major physiochemical factors affecting oral drug absorption.

Systemic Routes of Administration: Parenteral

Parenteral administration is outside the gastrointestinal tract.
Absorption phase following parenteral administration is either avoided or occurs at the site of administration.
Examples include intravenous, intraarterial, intramuscular, subcutaneous, intrathecal, transdermal, and intranasal.

Systemic Routes of Administration: Enteral

Enteral administration is inside the gastrointestinal tract.
After oral administration, absorption occurs throughout the intestinal tract.
The small intestine (especially the jejunum) is the major site of absorption.
Examples include buccal, sublingual, oral (PO), and rectal.

Routes of Administration Requiring Absorption

Some routes of administration do not require absorption (e.g., intravenous, intraarterial, intrathecal).
Other routes require absorption. Examples include intramuscular, subcutaneous, oral, buccal, sublingual, transdermal, and intranasal.

Oral Absorption

Oral route advantages: convenient and palatable dosage forms, less expensive than parenteral formulations, and administration in outpatient settings.
Oral route disadvantages: can be inefficient due to multiple barriers to systemic circulation, potential significant local side effects, and variable absorption altering pharmacokinetic profiles.

Sites of Absorption after Oral Administration

Stomach: pH 1-3, length 0.3m, transit time 0.5 hr, surface area 0.2m².
Duodenum: pH 5.8-6.5, length 0.3m, transit time <0.1 hr, surface area 0.02m².
Jejunum: pH 6-8, length 2.5m, transit time 2-3 hr, surface area ~200m².
Ileum: pH 7-8, length 3.5m, transit time 1 hr, surface area ~3m².
Large Intestine: pH 5.5-7, length 1.5m, transit time 10-36 hr, surface area ~3m².
The small intestine, especially the jejunum, is the major site of absorption due to a higher surface area, permeability, and blood flow.

Oral Bioavailability

Oral bioavailability (F) is the fraction of a drug that reaches the bloodstream after oral administration.
It represents the amount of drug escaping the intestine and avoiding the first-pass effect.
F = FF × FG × FH, where FF is the fraction absorbed from the intestine, FG is the fraction escaping the intestine wall, and FH is the fraction escaping the liver.

Factors Affecting Oral Absorption: Physiologic

Patient factors:
- Gastric emptying time.
- Intestinal transit time.
Drugs:
- Solubility/dissolution rate.
- Molecular size.
- Lipophilicity.

Factors Affecting Oral Absorption: Physiologic - Details

Gastric Emptying:
- Accelerators: Liquids, Prokinetic drugs (e.g., metoclopramide).
- Delays: Food (high fat), Diarrhea, Diabetic gastroparesis, Anticholinergic drugs, Opioids, Constipatation
Intestinal Transit Time:
- Accelerators: Diarrhea
- Delays: Constipation, Anticholinergic drugs, Opioids

Factors Affecting Oral Absorption: Physiochemical

Solubility/Dissolution: Ability of a drug to dissolve in an aqueous environment, influence by factors like particle size, salt formation.
Molecule Size: Smaller molecules are generally better absorbed.
Lipophilicity: Ability to dissolve in lipids – balance is crucial for absorption.
Dissolution: Rate is calculated by the Noyes-Whitney equation (Dissolution Rate = D * S (Cs – C) / h). Important variables are diffusion coefficient (D), surface area (S), drug solubility (Cs), concentration of drug in the intestines (C), and diffusion layer thickness (h).
Formulation impacts dissolution rate. Solutions > Capsules > Tablets > Extended-release Tablets

Biopharmaceutical Classification System

Categorizes drugs into 4 classes based on solubility and permeability.
Class IV drugs are not typically used in oral formulations.
Class I: rapid absorption (no apparent rate-limiting step).
Class II: dissolution is the rate-limiting step.
Class III: permeability is the rate-limiting step.

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Description

This quiz covers the essential concepts of drug absorption and various routes of administration, including oral and parenteral methods. It aims to help you identify different administration routes and understand their physiological and physicochemical factors influencing absorption. Test your knowledge on this crucial aspect of pharmacology!