chapter 2 principles of drug action

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Transcript chapter 2 principles of drug action

Principles of Drug Action
Medical Math
Chapter 2
Buffy Ryan, RN
Drug Action
• The chemical in a drug combines with or
alters the molecules in body cells so that it
changes the way the cells work.
• The 4 main drug actions are:
• 1. Depressing
• 2. Stimulating
• 3. Destroying cells
• 4. Replacing substances
Drug Action
• Drugs usually speed up or slow down the
ordinary processes the cells carry out
• Example: antihistamines slow the body’s
natural reactions to irritation, and stimulants
speed up the energy-producing functions of
cells
Drug Action
• Some drugs destroy certain cells or parts of
cells
• Example: antibiotics kill disease
microorganisms; 5FU and methotrexate kill
cancer cells
Drug Action
• Some drugs action is to replace or
supplement natural substances that the body
lacks due to organ malfunction or poor
nutrition
• Example: Potassium chloride and calcium
carbonate
4 Basic Body Processes That
Affect Drug Action
Absorption
Distribution
Metabolism/Biotransformation
Excretion
Absorption
• Absorption is the passage of a drug from
the site of administration into the
bloodstream
• How quickly a drug is absorbed is important
because it determines how soon it will start
it’s action
• The route of administration can affect the
rate of absorption
Absorption
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Route of Administration
Sublingual(under tongue)
Oral(by mouth)
Subcutaneous
Intramuscular
Intravenous
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Absorption begins
In the mouth
In the stomach/intestine
Under the skin
In the muscle
In the blood stream
Distribution
• Distribution is the transport of the drug
from the bloodstream to the body tissues
and intended site of action
• Some of the drug passes through the
capillaries thin walls (alcohol passes easily
thru capillaries and into tissues quickly)
• Distribution time varies with different drugs
Metabolism/Biotransformation
• This is a series of chemical reactions that
inactivate a drug by converting it into a
water-soluable compound so it can be
excreted by the body
• Sort of like digesting food, the body uses
enzymes to break down the drug and
detoxify toxic substances
• The liver is where most metabolism takes
place , some occurs in the lungs, intestines,
kidneys, & blood
Excretion
• Excretion is the body’s way of removing the
waste products.
• Most drugs leave the body through the
kidneys and large intestine
• The lungs, sweat, hair, and milk glands also
excrete
• An elderly person with kidney disease has
an increased risk of toxicity….WHY?
Patient Education Concerning Excretion
Increase fluid
intake to aid in
excretion
Cough & deep
breathe after
anesthesia
Chew gum or
hard candy to
decrease
Avoid laxatives, Keep skin clean Unpleasant taste
they speed up
to avoid
from excretion
drug excretion irritation from
via saliva
excretion(sweat)
Improper diet & Pregnant or
lack of activity nursing moms
slow excretion should check
with MD
Factors Affecting Drug Action
AGE
• Infants body systems
are immature
• The body systems of
the elderly may have
decreases in kidney
and liver function
• Smaller doses may be
required to treat the
young and old
SIZE
• The average adult dose
is calculated for a
person age 15-65
weighing 150lbs
• As a result, doses for
the young, elderly, or
obese must be
calculated by body
weight
DIET
• Combining certain
foods with certain
drugs can alter the
effects
• EX: Tetracycline/Milk
• Coumadin/Vitamin K
SEX
• Women are generally
smaller than men and
have more body fat
• Pregnant women must
always consult their
physician because of a
drugs risk to the fetus
GENETIC FACTORS
• Heredity can affect a
persons metabolism
and excretion process
• Some people lack the
naturally occurring
enzymes to break
down drugs for
excretion
PATHOLOGICAL
CONDITIONS
• Diseases can strongly
affect how patients
respond to drugs
• Heart disease, kidney
failure, diabetes, and
low blood pressure
can affect drug action
• Cancer can also affect
drug action, requiring
a stronger dose
PSYCHOLOGICAL FACTORS
• A positive attitude is
likely to respond well
to medication
• Some patients have
taken a placebo and
reported feeling better
• Strong feelings such
as worry, anger, fear
or jealousy can affect
drug action
ROUTE OF
ADMINISTRATION
• A drug acts more
quickly when injected
directly into the
bloodstream
• Medications taken by
mouth take the longest
time to show effects
TIME OF ADMINISTRATION
• Important to give
meds at time they
were ordered
• Some drugs need to be
taken with a meal,
others are absorbed
more quickly on an
empty stomach
DRUG-TAKING HISTORY
• A patient can build up
a tolerance to a
particular drug
• Some drugs can
interact with each
other
• Always check
allergies
ENVIRONMENTAL
CONDITIONS
• Heat and cold can
affect drug action
• Heat relaxes the blood
vessels, speeds up
circulation, drugs act
faster
• Cold slows action by
constricting vessels
DRUG EFFECTS
Drug Effects
• Therapeutic effect – what you want
• Side effect – what you may get along with
the therapeutic effect (some good, some
bad)
• Ex: Morphine – therapeutic effect – kills
pain, side effect – respiratory
depression/constipation/urine retention
Classification of
Drug Effects
• Local – affects mainly the area it enters or is
applied. Benadryl ointment applied to a bug
bite on skin.
• Systemic – travel throughout bloodstream to
affect cells or tissues. Benadryl capsule
taken by mouth due to allergic rash.
Adverse Reactions
• What you don’t want!!!
• Idiosyncrasy – opposite of expected
effect
• Tolerance – lessened effect
• Cumulation – stronger effect
• Toxicity – different symptoms affecting
organs
• Synergism – stronger effect when more
than one drug taken
Adverse Reactions
• Antagonism – weaker effect when more
than one drug taken (tetracycline & antacid)
• Potentiation – effect of one drug increases
effect of another drug (tylenol & codeine)
• Interaction – therapeutic or adverse effect
on body
• Physical dependence – physical need for a
drug
• Psychological dependence – mental craving
for drug