Transcript pharmintro

Principles of Pharmacology
SOURCES AND NAMES OF DRUGS
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Sources of Drugs
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Many drugs are isolated from plants or
chemically derived from plant substances.
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Names of Drugs
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Chemical Name
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Chemical description of the molecule
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e.g., acetylsalicylic acid
Generic Name
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The legal or official name, listed in the USP
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e.g., aspirin
Brand Name
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Trademark belongs to the manufacturer
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e.g., Exedrin
CATEGORIES OF DRUGS
AND DRUG IDENTIFICATION
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Drug Classification Systems
 Chemical Structure
 Pharmacological Actions
 Clinical/Behavioral Effects
For our purposes, the most practical
classification system is by effects on
the user.
QUANTIFYING DRUG EFFECTS
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Pharmacodynamics
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the physiological actions of drugs
Dose-Response Relationships
 Efficacy (ED50 = median effective dose)
 Lethality (LD50 = median lethal dose)
 Therapeutic Index = LD 50 /ED 50
DOSE RESPONSE FUNCTIONS
QUANTIFYING DRUG EFFECTS
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Potency
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The amount of drug required to produce a particular
response
NOT the same as efficacy
Potencies of different drugs are compared by
comparing the ED50 ’s of each drug.
Time-Dependent Factors in Drug Actions
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Several factors may prolong or maintain a drug’s
effects.
DOSE RESPONSE FUNCTIONS
PERCENT EFFECT
100
A
B
C
75
50
25
0
0.1
1
10
DOSE (mg/kg)
100
300
MOVEMENT OF DRUGS IN THE BODY
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Pharmacokinetics
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Several factors influence the movement of drugs
through the body to target sites of action
Pharmacokinetics is the study of factors that
influence:
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Absorption from tissue sites to bloodstream
Distribution throughout the body
Metabolism (detoxification, breakdown)
Elimination of metabolic waste products
DRUG ABSORPTION
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A Little Chemistry
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Lipid solubility
pKa = pH at which 50% of drug molecules are
ionized (charged).
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Only uncharged molecules are lipid soluble.
The pKa of a molecule influences its rate of
absorption through tissues into the bloodstream.
pH varies among tissue sites (e.g., stomach pH is 34, intestinal pH is 8-9)
DRUG ABSORPTION
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Routes of
Administration
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Oral administration (P.O.)
Injection (I.M., I.V., S.C., I.P.)
Inhalation
Other mucous membrane
routes
 Intranasal, Sublingual,
Rectal
Topical (skin surface)
DRUG ABSORPTION
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Oral Drug Administration
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Advantages:
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relatively safe, economical, convenient, practical
Disadvantages:
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Blood levels are difficult to predict due to multiple
factors that limit absorption.
Some drugs are destroyed by stomach acids.
Some drugs irritate the GI system.
INJECTION ROUTES
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Advantages of Injection Routes
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Absorption is more rapid than with oral
administration.
Rate of absorption depends on blood flow to particular
tissue site (I.P. > I.M. > S.C.).
Advantages specific to I.V. injection
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No absorption involved (inject directly into blood).
Rate of infusion can be controlled.
A more accurate prediction of dose is obtained.
INJECTION ROUTES
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Disadvantages/Risks of Injection
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A rapid onset of action can be dangerous in
overdosing occurs.
If administered too fast, heart and respiratory
function could collapse.
Drugs insoluble in water or dissolved in oily
liquids can not be given I.V.
Sterile techniques are necessary to avoid the
risk of infection.
DRUG DISTRIBUTION
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Cell Membranes
Capillaries
 Drug affinities for plasma proteins
 Bound molecules don’t cross capillary walls, while
unbound molecules are free to pass through cell
membranes to sites of action
Blood Brain Barrier
 Tight junctions in capillaries plus glial cells
surrounding capillaries
 Less developed in infants
 Cerebral trauma can decrease integrity of BBB
Placenta
 Not a barrier to lipid soluble substances.
DRUG DEACTIVATION
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Metabolism and Excretion
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Liver microsomal enzymes
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Drug metabolism differs by age and gender due
to differences in microsomal enzyme systems.
Two-stage kidney process (filter, absorption)
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Some drugs have active (lipid soluble)
metabolites.
DRUG DEACTIVATION
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Drug Half-Life
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The half-life of a drug is the amount of time
required for half the drug to be eliminated from
the body.
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A drug with a half-life of 30 minutes is eliminated.
It takes approximately 6 half-lives for a single drug
dose to be eliminated.
Some drugs are eliminated at a constant rate, and
therefore do not have half-lives (e.g. alcohol).