Pharmacokinetics: A Tutorial Study Guide

Nicoladie Tam

• Publisher: Nicoladie Tam, Ph.D.
• eBook ISBN: 9781301010776
• Topic: Medicine
• Subtopic: Pharmacology

"Pharmacokinetics" is a part of the college-level Neuropsychopharmacology course series textbooks. It is a tutorial written in questions and answers format to describe the pharmacokinetics, drug interactions and drug-binding.

It is a study guide with in-depth explanations. Each section is a modular unit that is self-contained for easy reading. The principles and concepts are introduced systematically so students can learn and retain the materials intuitively.

1.Pharmacokinetics

Objectives

• Understand the factors affecting drug distribution
• Understand the factors affecting drug elimination

Concepts to Learn

• Routes of drug administration
• Oral, sublingual, inhalation, intravenous, intraperitoneal, intracranial, intramuscular, subcutaneous, topical administration
• Time course of drug distribution
• Depot binding
• Silent receptors
• Half-life of drug
• Plasma steady-state level of drug
• Therapeutic drug monitoring
• Periods of drug administration
• Duration of drug effects
• Factors affecting drug distribution
• Factors affecting drug absorption
• Ionization of drugs
• Lipid solubility
• Drug metabolism
• Synthetic reactions
• Non-synthetic reactions
• Conjugation groups
• Biotransformation
• Drug excretion
• Drug tolerance
• Pharmacological mechanisms in tolerance
• Behavioral mechanisms in tolerance
• State-dependent learning
• Cross-tolerance
• Placebo effects
• Blood-brain barrier
• Placental barrier

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1.1.Route of Administration

Objectives

• Understand the different routes in which drugs are administered into the body
• Understand the characteristics of these routes of administration

Concepts to Learn

• Oral administration
• Sublingual administration
• Inhalation
• Intravenous administration
• Intraperitoneal administration
• Intracranial administration
• Intramuscular administration
• Subcutaneous administration
• Topical administration

Drugs can be administered into the body through many different routes. Each route of administration has its own characteristics in terms of the distribution and absorption of the drug.

Oral administration is delivering the drug through the gastrointestinal tract. Because it goes through the stomach, the absorption is delayed until it reaches the small intestine. The rate-limiting step is the gastric emptying. It takes between 30 min to 2 hours for drugs to be absorbed, depending on whether the stomach is full or not. Because the stomach contains gastric juice, which is highly acidic, it can alter the absorption and effectiveness of the drug. Ionization of drug can affect the absorption rate. The acidic medium can also disintegrate the drug molecule.

Sublingual administration is delivering the drug by dissolving it under the tongue. It is absorbed in the buccal cavity. This bypasses the GI tract and avoids the acidic environment in the stomach, which may disintegrate the drug if swallowed.

Inhalation is administering the drug through breathing into the lungs. Absorption occurs at the alveolar interface through simple diffusion into the capillaries. The time to reach the target site is short for inhalation because drug molecules are carried by the pulmonary veins into the left ventricles, and into the arteries directly. Compared to intravenous administration, drug molecules are carried by veins into the right ventricles, and then are circulated through the pulmonary system in the alveolae before they are pumped into the arteries.

Intravenous administration is administering the drug by injecting into the vein. The absorption rate is fast because it is delivered by the circulatory system. Injection of drug into the system directly can be overdosed easily without means of recall if the injection rate is too high. It is highly susceptible to infection compared to other routes of administration.

Intraperitoneal administration is administering the drug into the peritoneal (abdominal) cavity. The interstitial fluid in the peritoneal cavity can acts as a buffer for the absorption of drug.

Intracranial administration is delivering the drug into the brain directly. This is often done in experimental animal in which drug is delivered through a cannula into specific site in the brain to test for its effects. It also bypasses the blood-brain-barrier (BBB), which often restricts a lot of chemicals from entering the brain from the peripheral system. The absorption rate is also fast.

Intramuscular administration is injection of drug into the muscle. The drug is slowly diffused into the capillaries. The rate of absorption is also depending on the vasoconstrictive (or vasodilative) property of the drug. If the drug causes vasoconstriction, such as cocaine, it slows down the absorption. If it causes vasodilation, the absorption is greatly increased.

Subcutaneous administration is injecting the drug under the skin. This is often done in veterinary medicine for injecting vaccines into the animal.

Topical application is the transdermal delivery of drug by applying onto the skin surface. Drug is absorbed through the skin. Drug can also be delivered through the absorption in the mucous membrane, such as the inside of the nose, rectal, vaginal or penile mucous membrane.

Summary

There are many different routes of administration, including: oral administration, sublingual administration, inhalation, intravenous, intraperitoneal, intracranial, intramuscular administration, subcutaneous and topical administration. They all have different characteristics of absorption, buffering and distribution rate.

Q&A

What is pharmacokinetics?

Pharmacokinetics includes the factors influencing the drug absorption, drug distribution, drug metabolism, and drug elimination.

The dose-response curve is often used to describe the pharmacokinetics. It is similar (although not exactly equal) to drug effect.

What is pharmacodynamics?

Pharmacodynamics is the dynamical interaction of the drug-receptor complex at the molecular level.

It is the mechanism of action that produces the biochemical and physiological effects. It is similar (although not exactly equal) to drug action.

What is route of administration of drug?

It is the method of delivering drug into the body.

Examples of route of administration are: oral administration, sublingual administration, inhalation, intravenous, intraperitoneal, intracranial, intramuscular administration, subcutaneous and topical administration.

What are the characteristics of...

Table of contents

• Preface
• 1.Pharmacokinetics
• About the Author
• Other Books Published by the Author