chapter 1 drugs/agents and factors affecting their action

Chapter 1

Drugs/Agents and Factors Affecting Their Action

Copyright 2007 Thomson Delmar Learning, a division of Thomson Learning Inc. All rights reserved.

Pharmacology

Study of the history, sources, and physical and chemical properties of drugs

Also looks at the ways in which drugs affect living systems

Various subdivisions of pharmacology have evolved

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Pharmacodynamics

Study of the biochemical and physiological effects of drugs

Study of drugs’ mechanisms of action

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Pharmacokinetics

Study of the absorption, distribution, biotransformation (metabolism), and excretion of drugs

Four steps Absorption Distribution Metabolism Excretion

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Pharmacotherapeutics

Study of how drugs may best be used in the treatment of illnesses

Study of which drug would be most appropriate or least appropriate to use for a specific disease; what dose would be required; etc.

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Pharmacognosy

The study of drugs derived from herbal and other natural (plant and animal) drug sources

Studying compositions of natural substances helps to gain knowledge for developing synthetic versions

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Toxicology

Study of poisons and poisonings All drugs have the potential to become

toxic.

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History of Pharmacology

Ancient Egypt: the cradle of pharmacology

These medical sources listed over 700 different remedies for different ailments.

First century: Dioscorides prepared De Materia Medica:

Listed and classified 600 different plants used for medicinal purposes; first time plants were ever classified

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Sources of Drugs

Drugs derived from: Natural sources Semisynthetic sources Synthetic sources

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Drug Uses

Symptomatic treatment Prevention Diagnostic drugs Curative Health maintenance Contraception

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Dosage Forms

Tablets Timed or sustained release Tablets or controlled release Capsule Troches Suppositories

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Dosage Forms

Solutions Douche Suspensions Emulsions Topicals

Patches Drug implants

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Parenteral Product Packaging

Ampules Sterile Sealed glass or plastic container Contain a single liquid dose

Vials: either single or multiple dose Glass or plastic container Sterile liquid dose Sealed with a rubber diaphragm

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Drug Names

Chemical name The drug’s chemical composition and

molecular structure Generic name (nonproprietary name)

Name given by the United States Adopted Names Council

Allows the drug to be marketed

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Brand Name

Also called trade name (proprietary name)

The drug has a registered trademark; use of the name is restricted by the drug’s owner

(usually the manufacturer) Allows the drug to be commercially

distributed The superscript ® is registered by the U.S.

Patent Office and approved by the FDA (Food and Drug Administration)

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Drug Names: Examples

Chemical name (+/-)-2-(p-isobutylphenyl) propionic acid

Generic name Ibuprofen

Trade name Motrin

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U.S. Drug Legislation

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Pure Food and Drug Act of 1906 Required all drugs to meet minimal

standards Federal Food, Drug, and Cosmetic Act of

1938 Required the drug to be safe before being

distributed over state lines

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U.S. Drug Legislation(continued)

1970: Comprehensive Drug Abuse Prevention and Control Act

Also known as Controlled Substance Act: classified drugs according to their abuse potential

Regulates the manufacture and distribution of drugs causing dependence

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Controlled Substances Schedules

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Schedule I High potential for abuse

No medical use HeroinLSD

Schedule II High potential for abuse

Accepted medical use

MorphineDemerol

Schedule III Lower potential for abuse


Librium, Valium, hydrocodone, Tylenol with codeine

Schedule IV Lower potential for abuse


LibriumValium

Schedule V Lowest potential for abuse


LomotilRobitussin A-C


Prescription Drugs

Prescription drugs = legend drugs Drugs prescribed by:

Physician Nurse practitioner Physician’s assistant Dentist Veterinarian Others

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Principles of Drug Action

Drugs Alter existing cellular or chemical functions Exert their action by forming a chemical

bond with specific receptors within the body Referred to as a lock and key effect

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Drug receptor interaction. Binding with specific receptors occurs only when the drug and its receptors have a compatible chemical

shape.

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Receptors The better the fit, the stronger the drug’s

affinity, thus Drug effect occurs at lower doses

(continued)

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Agonist effect Antagonistic effect Adverse drug effect Therapeutic effect

(continued)

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Pharmacokinetics: Absorption

Routes Oral Parenteral Topical

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Metabolism: First-Pass Effect

The metabolism of a drug and its passage from the liver into the circulation

Metabolism occurs in the liver Liver enzymes react with the drug Increases the dosage requirement

The same drug—given IV—bypasses the liver, preventing the first-pass effect from taking place, and more drug reaches the circulation.

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Pharmacokinetics: Distribution

The transport of a drug in the body by the bloodstream to its site of action

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Elimination/Excretion

The elimination of drugs from the body Kidneys (main organ) Liver Bowel

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Renal excretion of drugs. Note sites where drugs are secreted and

reabsorbed.

(continued)

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Pharmacokinetics:Measuring Drug Action

Half-life The time it takes for one half of the original

amount of a drug to be removed from the body

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chapter 1 drugs/agents and factors affecting their action

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