Ppt chapter 05

Chapter 5
Adverse Effects and Drug
Interactions
Copyright © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins

Question
• All drugs have some type of adverse effect(s).
– A. True
– B. False

Answer
• A. True
• Rationale: All drugs produce some type of adverse
effect; some of the effects are mild, and others can
be life threatening.

Adverse Effects
• An adverse effect of drug therapy is a usually undesirable
effect other than the intended therapeutic effect.
• It may occur even with normal drug dosing.
• An adverse effect may result from
– Too much of a therapeutic effect
– Other pharmacodynamic effects of the drug

Drug Interactions
• A drug interaction occurs when two drugs or a drug and
another element have an effect on each other.
• This interaction may
– Increase or decrease the therapeutic effect of the
drugs
– Create a new effect
– Increase the incidence of an adverse effect

Adverse Effects
• Every drug can produce adverse effects.
• Serious adverse effects lead to the withdrawal of a small
number of drugs from the market every year.
• It is important for nurses and other health care
professionals to be alert for adverse effects from drug
therapy.
• Serious adverse reactions to a drug, especially a newly
approved drug, should be reported to a national
database.

Allergic and Idiosyncratic Response
• An allergic response is an immune system response.
• The antigen–antibody response when the drug is taken
again
• Symptoms may become more severe each time the drug
is introduced into the body.
• The most serious allergic response is called anaphylaxis.
• Idiosyncratic responses are unusual and in fact may be
the opposite of what is anticipated.

Question
• Which of the following is not a symptom of anaphylaxis?
– A. Bronchospasms
– B. Vasodilation
– C. Convulsions
– D. Pruritus

Answer
• D. Pruritus
• Rationale: Pruritus is itching and is not a sign of
anaphylaxis but is considered an allergic reaction.

Toxicities
• Neurotoxicity (central nervous system)
– Signs and symptoms: drowsiness, auditory and visual
disturbances, and seizures
• Hepatotoxicity (liver)
– Manifestations include hepatitis, jaundice, elevated
liver enzyme levels, and fatty infiltration of the liver.
• Nephrotoxicity (kidneys)
– Signs and symptoms: decreased urinary output,
elevated blood urea nitrogen, increased serum
creatinine, altered acid-base balance, and electrolyte
imbalances

Toxicities (cont.)
• Ototoxicity (eighth cranial nerve)
– Signs and symptoms: tinnitus, hearing loss, light-headedness,
vertigo, nausea, and vomiting
• Cardiotoxicity (heart)
– Signs and symptoms: irregularities in conduction,
heart failure, and damage to the myocardium
• Immunotoxicity (immune system)
– Signs and symptoms: immunosuppression, increased
incidence of bacterial, viral, and parasitic infections

Drug Interactions
• Drug interactions occur when one drug is affected in
some way by another drug.
• Drug interactions may be beneficial.
• Negative effects from drug interactions are those that
decrease the therapeutic effect.
• Drug interactions may take place in any phase of
pharmacokinetics.
• Drug interactions can also change the pharmacodynamics
of a drug.

Drug Interactions (cont.)

Drug Interactions Affecting Absorption
• Drug absorption is often decreased because of drug
interactions.
• If a drug binds with another substance in the GI tract,
less of the drug is available to be absorbed.
• This binding of a drug is termed chelation.
• Drug absorption may also be increased as a result of a
drug interaction or the presence of food in the GI tract.
• The exact extent of changes in drug absorption caused by
drug interactions is often difficult to predict.

Drug Interactions Affecting Distribution
• Distribution is affected by two types of drug interactions.
• The first is competitive protein binding.
• The second is drug alteration of the extracellular pH.

Drug Interactions Affecting Metabolism
• Probably the most important and common drug
interaction is one that alters the metabolism of a drug.
• Drugs that induce a hepatic enzyme increase the amount
of that enzyme in the liver.
• If two drugs that affect the cytochrome P-450 system
must be administered to a patient together, the dose of
one of the drugs may have to be adjusted.

Drug Interactions Affecting Excretion
• Drugs can alter renal filtration, renal reabsorption, or
renal secretion.
• Glomerular filtration is dependent on blood flow to the
kidney.
• Drugs that decrease cardiac output decrease the amount
of circulating blood that is sent to the kidneys.
• Renal reabsorption of a drug is dependent on whether a
drug is ionized.

Drug Interactions Affecting
Pharmacodynamics
• Drug interactions may affect the pharmacodynamics of
one or both drugs administered.
• The overall effect may be positive or negative.
• The drug that has the weaker affinity for the receptor will
not be able to exert its therapeutic effect.

Additive Effect
• An additive effect occurs when two or more “like” drugs
are combined.
– Example: Codeine with acetaminophen work together
to produce better pain control.
• An additive effect may be intentional or may
unintentionally cause harm.
– Example: Alcohol and aspirin can both cause GI
bleeding; taken together they greatly increase the
risk.

Synergistic Effect
• A synergistic effect occurs when two or more “unlike”
drugs are used together to produce a combined effect.
• Consider the following example:
– A beneficial synergistic effect occurs when two
different types of antibiotics that work in very
different ways are combined, such as penicillin G and
an aminoglycoside antibiotic.

Potentiated Effect
• Potentiation is an interaction in which the effect of only
one of the two drugs is increased.
• In other words, a drug that has a mild effect enhances
the effect of a second drug.
– Example: Hydroxyzine increases the effect of
morphine.

Antagonistic Effect
• An antagonistic drug interaction is the opposite of a
synergistic effect.
• It results in a therapeutic effect that is less than the
effect of either drug alone because the second drug
either diminishes or cancels the effects of the first drug.
• Antagonistic interactions can also occur at receptor sites.
– Example: Protamine reverses the action of heparin.

Question
• When naloxone is given with morphine, it causes what
type of drug reaction?
– A. Additive effect
– B. Synergistic effect
– C. Potentiated effect
– D. Antagonistic effect

Answer
• D. Antagonistic effect
• Rationale: Antagonistic interactions can also occur at
receptor sites. Naloxone is a narcotic antagonist used
to correct narcotic overdosage by displacing the
morphine molecule off the receptor site.

Drug Incompatibilities
• Chemical incompatibilities
– Chemical incompatibilities between drugs change
both the drug’s structure and its pharmacologic
properties.
• Physical incompatibilities
– Physical incompatibilities occur when two drugs are
mixed together.
– The mixture results in the formation of a precipitate.

Assessment of Core Patient Variables
• Health status
– Concurrent medical conditions may increase the risk
of adverse effects from drug therapy.
– A patient’s chronic health condition may also
necessitate drug therapy that may interact with other
drugs.
• Life span and gender
– A patient’s age can greatly increase the risk of
adverse effects from drug therapy.
– In addition, older adults are more likely to be
receiving polypharmacy for multiple chronic illnesses.

(cont.)
• Lifestyle, diet, and habits
– The patient’s lifestyle, diet, and other health habits
can have an impact on drug interactions.
• Environment
– The patient’s environment may increase the
likelihood that a certain adverse effect will occur.
– For instance, some antibiotics can cause the adverse
effect of photosensitivity.
– The environment in which drug therapy is
administered can also play a role in the early
detection of adverse effects.

(cont.)
• Culture and inherited traits
– Researchers are beginning to study responses to
drug therapy that are genetically determined in
various ethnic and racial populations.
– These responses may place the patient at greater
risk than the rest of the global population for adverse
effects or drug interactions.

Nursing Diagnoses and Outcomes
• Risk for Infection related to drug-induced myelosuppression
– Desired outcome: The patient will not develop infection
while on drug therapy.
• Imbalanced nutrition: Less Than Body Requirements related to
drug-induced nausea, vomiting, anorexia, stomatitis
– Desired outcome: Despite adverse effects, the patient
will receive enough nourishment to meet physiologic
needs.
• Risk for Poisoning (Toxicity) related to use of drug with a
narrow therapeutic index
– Desired outcome: The patient will receive drug therapy
without harmful or poisonous effects.

Planning and Intervention
• Maximizing therapeutic effects
– When drug interactions are intentional and desirable,
it is important to give the drugs at the prescribed
time intervals.
• Minimizing adverse effects
– To help protect the patient from serious adverse
effects and drug interactions, obtain a drug history
from the patient.
– If a patient is taking a drug that may interact with
another drug, the drugs should not be
coadministered.
– Throughout therapy, monitor the patient for signs
and symptoms of interactions and adverse effects.

Providing Patient and Family Education
• Inform the patient and family about adverse effects and
drug interactions.
• Initial instruction includes teaching the patient how to
minimize the occurrence of these effects.
• Teach the patient which effects to expect, which to report
to the prescriber, and which require immediate medical
attention.

Assessment and Evaluation
• During drug therapy, monitor for adverse effects and
drug interactions.
• Consider the possibility of a drug interaction each time a
new drug is added to the treatment plan.

Ppt chapter 05

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