Download Chapter 4 - Wolters Kluwer Health

Chapter 4
How Drugs Work
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Local and Systemic Effects
• Drugs with local effects
– Used to treat one specific area of body
– Can have systemic side effects
Learning Objective 4-1
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Examples of Drugs with Local Effects
• Lidocaine injection: numbs patient’s jaw for dental work
• Lidocaine patch: relieves pain of shingles
• Bacillus Calmette-Guérin (BCG) solution: prevents and
treats bladder cancer tumors
• Corticosteroid creams: counteracts inflammation caused
by eczema
• Benzoyl peroxide: mild acne treatment
Learning Objective 4-1
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Local and Systemic Effects (cont’d)
• Drugs with systemic effects
– Travel through bloodstream to reach specific body
tissues
– Target specific body systems; may have effects on
other systems also
Learning Objective 4-1
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Common Drugs and the Body’s Systems
• [Insert untab4-1]
Learning Objective 4-1
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How Drugs Work in the Body
• Solid forms of drugs go through three phases
– Pharmaceutic phase
– Pharmacokinetic phase
– Pharmacodynamic phase
Learning Objective 4-2
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How Drugs Work in the Body (cont’d)
• Liquid forms of drugs go through two phases
– Pharmacokinetic phase
– Pharmacodynamic phase
Learning Objective 4-2
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The Pharmaceutic Phase—Entering the
Body
• Drug breaks into small particles in gastrointestinal tract
• Drug dissolves and releases medication into body
• Drugs in solid form turn into form body can take in and
use
Learning Objective 4-2
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The Pharmaceutic Phase—Entering the
Body (cont’d)
• Some tablets are made to dissolve in stomach acids
• Time-release capsules and extended release capsules are
made to dissolve very slowly in stomach
• Enteric coated tablets do not break apart until in alkaline
environment of intestines
Learning Objective 4-2
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The Pharmacokinetic Phase—Entering the
Bloodstream
• Pharmacokinetics refers to activities involving drug within
body after it has been administered
• Happens after patient swallows pill or capsule and
medication dissolves
• Injected medications take effect so quickly because they
are ready for use immediately as liquids
Learning Objective 4-2
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The Pharmacokinetic Phase—Entering the
Bloodstream (cont’d)
• Drug goes through four activities inside body:
– Absorption
– Distribution
– Metabolism
– Excretion
Learning Objective 4-2
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Absorption
• Drug is taken into bloodstream through walls of stomach
or intestines
• Bloodstream carries drug to places in body that drug is
meant to reach and affect
• Speed of absorption depends on how drug is given, rate
at which drug dissolves, and conditions inside body
Learning Objective 4-2
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Absorption Rates by Administration
• Fastest absorption: inhalation, IV, sublingual
• Second-fastest absorption: IM injection
• Third-fastest absorption: SubQ injection
Learning Objective 4-2
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Distribution
• Bloodstream carries drug to target place
• Bioavailability: sometimes only part of drug is available
to do job once it reaches correct site
– Portions of drug may have been bound to protein in
blood
– Some drugs are not fat soluble and cannot cross
body tissues around brain, placenta, or testes
Learning Objective 4-2
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Metabolism
• Liver metabolizes drugs: takes out all important
chemicals body needs (active ingredients)
• Remaining ingredients are turned into substances body
can get rid of
• Liver cannot fully metabolize drug sometimes; if liver is
diseased, lower dosages may be required
Learning Objective 4-2
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Excretion
• Liver gets rid of inactive leftovers by sending to kidneys
• Kidneys excrete leftovers in urine
Learning Objective 4-2
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Excretion
• Some medications bypass liver and go straight to
kidneys; if kidneys are diseased, lower dosages may be
required
• Drugs that bypass liver and kidneys are eliminated
through sweat, breast milk, breathing, and feces
Learning Objective 4-2
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Half-Life
• Time it takes body to eliminate 50 percent of drug
– Drugs with short half-life are administered more
frequently
– Longer half-life drugs are administered less often
• Patients with liver or kidney disease may have problems
eliminating a drug; half-life may be longer for them and
toxic levels may build up
Learning Objective 4-2
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The Pharmacodynamic Phase—Going into
Action
• Drugs actions and effects within body
• Whole body is exposed to possible effects when traveling
through bloodstream
– Primary effect: intent of active ingredient
– Secondary effects: all other effects of drug
Learning Objective 4-2
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Drug Reactions
• Contraindications
• Adverse reactions
• Allergic reactions
• Idiosyncratic reactions
• Drug tolerance
• Cumulative drug effect
• Toxic reactions
Learning Objective 4-3
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Contraindications
• Contra = “against”, indication = “sign”
• Circumstances under which a drug or treatment should
not be used
Learning Objective 4-3
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Adverse Reactions
• Harmful side effects, or adverse reactions, may occur
when medications are taken
• May:
– Be mild, severe, or even life threatening
– Happen after the first dose, after several doses, or
after many doses
– Happen in a predictable way or without warning
Learning Objective 4-3
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Adverse Reactions
• [Insert figure 4-13]
Learning Objective 4-3
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Allergic Reactions
• Happen when patient’s immune system responds to drug
as if it were an antigen
• Immune system produces antibodies to combat invader
• Usually take time to build up; most occur after patient
has received more than one dose of drug
• Be aware of how allergies or reactions are flagged in
patients’ charts
Learning Objective 4-3
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Signs and Symptoms of Drug Allergies
• Itching and skin rash
• Urticaria (hives)
• Dyspnea
• Wheezing
• Cyanosis
• Swelling of eyes, lips, or tongue
• Sudden loss of consciousness
Learning Objective 4-3
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Idiosyncratic Reactions
• Response to drug is unusual and different from what is
normally expected
• It is unclear why some patients have idiosyncratic
responses to some medications
Learning Objective 4-3
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Drug Tolerance
• Decreased response to drug; same dosage no longer has
same effect
• Patients may need larger dosage of medication to get
desired results
Learning Objective 4-3
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Cumulative Drug Effect
• Part of medication dose remains active in body due to
body being unable to fully metabolize and excrete the full
dose before another one is taken
• Too much medication can build up in body and cause
harmful reactions
• Liver and kidneys are organs that metabolize and excrete
medications from body
Learning Objective 4-3
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Toxic Reactions
• Certain circumstances can produce toxic reactions of
most drugs
– Dosages too large
– Unsafe amount of drug remaining in bloodstream, or
above therapeutic level
– Kidneys are not working properly and cannot excrete
drug in patient’s urine
Learning Objective 4-3
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Angioedema
• Type of allergic reaction to medication
• Edema is abnormal build-up of fluid
• Angioedema appears as welts, or ridges, below skin
• Usually appear around eyes, lips, mouth, throat, and
sometimes other parts of body
Learning Objective 4-4
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Anaphylactic Shock
• Most serious allergic reaction to medication
• Requires immediate medical attention
• Usually occurs soon after patient is given drug to which
he is extremely sensitive
Learning Objective 4-4
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Signs and Symptoms of Anaphylactic
Shock
• [Insert untab4-2]
Learning Objective 4-4
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Drug Interactions
• Drug-drug interactions occur when one drug interacts
with or interferes with action of another drug
– Synergism: two drugs work together
– Antagonism: one drug reduces effects of another
drug
– Potentiation: one drug increases or prolongs effects
of another drug
Learning Objective 4-5
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Synergistic Drug Reactions
• Two or more drugs work together to produce an effect
greater than what each drug would have produced alone
• Combination medications take advantage of positive
aspects of synergism
• Negative effects can occur also
Learning Objective 4-5
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Antagonistic Drug Reactions
• One drug interferes with action of another drug either
canceling each other out or making one drug less
powerful
• Patients should be warned about antagonistic reactions
Learning Objective 4-5
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Obtaining a Patient’s Medical History
• Physician needs to be aware of all medications patient is
currently taking
• Patients should be encouraged to be forthcoming and
complete
• Ask patient if he has adjusted drug dosages on his own
• Explain need to know alcohol or drug use for potential
drug interactions; remind patient of confidentiality
Learning Objective 4-5
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Obtaining a Patient’s Medical History
(cont’d)
• If patient is unable to remember all medications:
– Ask for names of physicians, dentists, and other
health care professionals patient is seeing; this may
help with recall of prescriptions
– Have patient or family member collect patient’s
prescriptions and OTC medications and bring them to
next appointment
Learning Objective 4-5
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Drug Interactions (cont’d)
• Food-drug interactions occur when foods eaten interact
with or interfere with action of a drug
• Foods contain chemicals that affect body
• Patients need to know about any possible food-drug
interactions and adjust their diets accordingly
Learning Objective 4-6
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Drug Interactions (cont’d)
• Some medications should be taken on an empty stomach
– Food may interfere with absorption
• Some medications irritate stomach and cause nausea,
vomiting, or epigastric irritation
– Taking them with food is helpful
• Some drugs, when taken with certain foods, produce
enhanced effects in the body
Learning Objective 4-6
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Food-Drug Interactions
• [Insert untab4-3]
Learning Objective 4-6
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Factors Influencing Drug Responses
• Age
• Weight
• Gender
• Pre-existing disease or condition
Learning Objective 4-7
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Age
• Can affect dosage size
• Organs are more immature in children, so drug
metabolism is different
Learning Objective 4-7
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Weight
• Dosages calculated for average 150 pound patient
• Adjustments in dosage can be made for higher or lower
weight
Learning Objective 4-7
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Gender
• Females may require smaller dose than males due to
makeup of bodies
• Men and women differ in amount of body fat
• Males and females also differ in ratio of body mass to
body water
Learning Objective 4-7
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Pre-existing Disease or Condition
• Liver or kidney disease affects drug metabolism
• Pregnancy affects choice of medications due to ability to
cross placenta
Learning Objective 4-7
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