Download - General principles of drug action
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Chapter 2
General Principles of Drug Action
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General Factors that Characterize the action of all Drugs and that Determine the effective level of any
Therapeutic agent at its site of action
Route of administration Passage across body membrane Absorption Transport and distribution Molecular mechanism of drug action Drug metabolism excretion
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A. Route of administration
General Routes of Drug Administration
I. Enteral- (Oral and Rectal)
Oral Dosage forms: tablet, capsule, suspension,
solution, pills etc.
Area of Absorption: gastric and intestinal mucosa
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oral
Advantages - Safest
- Most convenient
- Cheapest
Disadvantages- Irritation of the gastric
mucosa- Destruction of some
drugs by the gastric acid
- Variable rate of absorption
- Slow rate of absorption
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II. Parenteral ( IV, IM, SC ID)
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Intravenous
Advantages- Most rapid and uniform
response- More predictable
response- Useful for
administering drugs that poorly absorbed by other routes
Disadvantages- Produces more side
effects- Drugs can not be
withdrawn once injected
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Sublingual routes
Area of absorption : oral mucous membrane Drug is placed under the tongue By- Passed effect Example of drug: Nitroglycerine
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B. Passage Across Body Membrane
Types of Body MembraneCell membraneIntracellular membraneBlood capillaries
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Composition Phospholipid (40%)Protein (50-60%
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Physiochemical propertiesLipid solubilityMolecular size and shapeDegree of ionization
pHPka
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Types of Passage ( Transport)
I. Passive transport Simple diffusion filtration
II Specialized transport Active transport Facilitated diffusion Pinocytocis
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C. Absorption
movement of molecules from the site of administration to the blood stream
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Factors Affecting Absorption
Physiochemical factors that affect passage Dosage form (bioavailability) Drug solubility Area of absorbing surface Drug concentration Blood flow
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D. Distribution
Movement of molecules from the blood stream to the different tissues of the body
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Factors Contributing to the unequal rate of Distribution
Plasma protein binding Cellular binding Storage in body fats Blood-Brain Barrier
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E. Molecular Mechanism of Drug action
Receptors
Affinity
Agonist
Antagonist
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Factors affecting Drug activity
1. Antagonism
a. pharmacologic
e.g. histamine + antihistamine
b. physiologic
e.g. diuretics + sympathomimetic amide
c. chemical
e.g. heparin + protamine
2. Additve effect
3. Potentiation
4. Cummulation
5. Tolerance /tachyphylaxis
6. Variation in drug response
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Drug Termination
Redistribution Excretion (kidney)
Amount of drug excreted by the kidney depends on the following process
1. passive tubular diffusion ( reabsorption)
2. active tubular secretion
3. filtration
*Metabolism
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Chapter 3 Adverse Drug Reactions
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Classification1. Toxic
a. exaggerated effect on target organ
b. effects on non target organ (side effect)c. effects on fetal development ( terratogenic)d. local reactione. drug interactions
2. Allergic reactions3. Idiosyncrasy4. Interference in natural defense mechanism