Transcript Characterization of Drug Action

Chapter 2
Drug Action and Handling
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Characterization of Drug Action
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Dose-Effect Curve
Intensity of the drug changes as the dose
changes.
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Intensity of the effect changes with time.
Desired therapeutic effect is related to dose.
Adverse and therapeutic effects are related to
dose.
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Figure 2-1 Dose-effect curve.
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Figure 2-2 Log dose-effect curve.
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Figure 2-3 Potency of agent.
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Drug Mechanism of Action
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Nerve Transmission
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Normally, an impulse travels along the nerve
and produces an action potential.
The action potential is triggered by the
neurotransmitter released at the previous
synapse.
Ultimately, the nerve transmission binds to a
receptor on a cell and enters the cell.
Once inside the cell, the message is given to
produce a response (i.e. increased heart rate).
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Drug Receptors
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When a drug combines with a receptor it
either enhances cell function or inhibits cell
function.
Drugs that enhance cell function are called
agonists.
Drugs that inhibit cell function are call
antagonists.
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Drug Agonists
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Have an affinity for a receptor
Combine with the receptor
Produce an effect
Naturally occurring neurotransmitters are
agonists
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Antagonists
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Competitive Antagonists – These drugs
have an affinity for the receptor, combine
with the receptor, and produce no effect
once attached to the receptor.
Noncompetitive Antagonists – These
drugs bind to a receptor site that is
different from the binding site of the
neurotransmitter or agonist. This reduces
the maximal response of the agonist.
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Antagonists
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Physiologic Antagonist – These drugs
have an affinity for a different receptor site
than the neurotransmitter or agonist. This
decreases the maximal response of the
agonist by producing an opposite effect by
means of different receptors.
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Routes of Drug Administration
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Enteral – Drugs are placed directly into the
gastrointestinal tract by oral or rectal
administration.
Parenteral – This type of drug administration
bypasses the gastrointestinal tract and
includes various injection routes, inhalation,
and topical preparations.
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Oral Routes of Administration
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Convenient, easy to use
Most widely accepted by Americans
Small intestine provides a large area for
drug absorption
Slower onset of action
Gastrointestinal adverse effects
Blood levels are less predictable
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Rectal Routes of Administration
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Good for patients who are vomiting or
unconscious
Can be used for local or systemic effects
Poor patient acceptance
Poor and irregular absorption of drugs
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Intravenous Routes of
Administration
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Produces the most rapid drug response
Can produce an almost immediate onset of action
Bypasses the absorption phase of the
pharmacokinetic process
Produces a more predictable drug response
Route of choice for an emergency situation
Disadvantages include phlebitis, local irritability,
drug irretrievability in the face of an allergic
reaction
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Pharmacokinetics
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Passage Across Body Membranes
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In order for a drug to be absorbed into the
body it must pass across different body
membranes.
 Drug passage across body membranes is
facilitated by several different transport
systems.
 The transport systems include passive transfer,
active transport, and facilitated diffusion.
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Pharmacokinetics – Absorption
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This is the process that transports drug
molecules from the site of administration to
the circulating blood.
Once in the circulating blood, drug
molecules must then pass through or
across biologic membranes.
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Drug Absorption
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Factors that Effect the Rate of Drug Absorption
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Physicochemical factors
 Site of administration
 Drug’s solubility
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Absorption from Oral
Dose Forms
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Dose form influences drug absorption.
Liquid dose forms are absorbed right away.
Tablets and capsules must be broken down
so that the drug can be released into the
gastrointestinal tract.
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Drug Release from Solid, Oral
Dose Forms
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Disruption
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Disintegration
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Tablet or capsule contents break apart.
Dispersion
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The tablet coating or capsule shell begins to
disintegrate.
Concentrated drug particles are spread
throughout the stomach or small intestine.
Dissolution
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The drug is dissolved in the gastrointestinal
fluid.
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Drug Distribution
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Distribution is the passage of drugs into target
organs, non-target organs, plasma, interstitial
fluids, intracellular fluids, brain, placenta, and
enterohepatic circulation.
Distribution is determined by the size of the organ,
drug solubility, plasma protein binding capacity,
and the presence of barriers.
The proportion of drug distribution to site of action
determines how quickly it will produce a response
and the duration of that response.
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Drug Metabolism
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Active parent compound is converted to an
inactive compound.
Active parent compound is converted to a
second active compound that is then.
converted to an inactive compound
Inactive parent compound is transformed
into an active compound.
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Drug Excretion
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Routes of Excretion
Kidneys
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Sweat
 Saliva
 Gingival crevicular fluid
 Respiratory tract
 Gastrointestinal tract
 Breast milk
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Factors that Effect
Pharmacokinetics
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Patient compliance
Age and weight
Sex
Pathologic state
Genetic variations
Placebo effect
Time or route of administration
Other drugs
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