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Chapter 38
Antibiotics Part 1
Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Infections: Sites of Origin

Community-associated infections

An infection that is acquired by a person who has not
been hospitalized or had a medical procedure (such
as dialysis, surgery, catheterization) within the past
year
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Infections: Sites of Origin (cont’d)

Health care–associated infections

Contracted in a hospital or institutional setting
 Were not present or incubating in the patient on
admission to the facility
 More difficult to treat because causative
microorganisms are often drug resistant and the most
virulent
 Occur in 10% of hospitalized patients
 MRSA most common
 Previously known as nosocomial
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3
Health Care–Associated Infections:
Prevention



Handwashing
Antiseptics
Disinfectants
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Health Care–Associated Infections:
Prevention (cont’d)

Disinfectant



Kills organisms
Used only on nonliving objects
Antiseptic


Generally only inhibits the growth of microorganisms
but does not necessarily kill them
Applied exclusively to living tissue
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Antibiotics


Medications used to treat bacterial infections
Ideally, before beginning antibiotic therapy, the
suspected areas of infection should be cultured
to identify the causative organism and potential
antibiotic susceptibilities
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Antibiotic Therapy



Empiric therapy: treatment of an infection before
specific culture information has been reported or
obtained
Definitive therapy: antibiotic therapy tailored to
treat organism identified with cultures
Prophylactic therapy: treatment with antibiotics
to prevent an infection, as in intraabdominal
surgery or after trauma
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Antibiotic Therapy (cont’d)

Therapeutic response


Decrease in specific signs and symptoms of infection
are noted (fever, elevated WBC, redness,
inflammation, drainage, pain)
Subtherapeutic response

Signs and symptoms of infection do not improve
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Antibiotic Therapy (cont’d)







Superinfection
Pseudomembranous colitis
Secondary infection
Resistance
Food-drug interactions
Host factors
Allergic reactions
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Antibiotics: Classes







Sulfonamides
Penicillins
Cephalosporins
Macrolides
Quinolones
Aminoglycosides
Tetracyclines
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13
Antibiotic Therapy:
Mechanism of Action




Interference with cell wall synthesis
Interference with protein synthesis
Interference with DNA replication
Acting as a metabolite to disrupt critical
metabolic reactions inside the bacterial cell
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Actions of Antibiotics


Bactericidal: kill bacteria
Bacteriostatic: inhibit growth of susceptible
bacteria, rather than killing them immediately;
will eventually lead to bacterial death
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Antibiotics: Sulfonamides


One of the first groups of antibiotics
Often combined with another antibiotic

Sulfamethoxazole combined with trimethoprim (a
nonsulfonamide antibiotic), known as Bactrim, Septra,
or co-trimoxazole and often abbreviated as SMXTMP, is used commonly in clinical practice
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Sulfonamides:
Mechanism of Action




Bacteriostatic action
Prevent synthesis of folic acid required for
synthesis of purines and nucleic acid
Do not affect human cells or certain bacteria—
they can use preformed folic acid
Only affect organisms that synthesize their own
folic acid
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Sulfonamides: Indications


Effective against both gram-positive and gramnegative bacteria
Treatment of UTIs caused by susceptible strains
of:

Enterobacter spp., Escherichia coli, Klebsiella spp.,
Proteus mirabilis, Proteus vulgaris, Staphylococcus
aureus
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Sulfonamides: Indications (cont’d)

Pneumocystis jirovecii pneumonia (PJP)



Co-trimoxazole
Upper respiratory tract infections
Sulfamethoxazole/trimethoprim is commonly
used for outpatient Staphylococcus infections,
due to the high rate of community-acquired
MRSA infections
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Sulfonamides:
Adverse Effects
Body System
Blood
Integumentary
Adverse Effects
Hemolytic and aplastic
anemia, agranulocytosis,
thrombocytopenia
Photosensitivity, exfoliative
dermatitis, Stevens-Johnson
syndrome, epidermal
necrolysis
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Sulfonamides:
Adverse Effects (cont’d)
Body System
GI
Other
Adverse Effects
Nausea, vomiting,
diarrhea, pancreatitis
Hepatotoxicity,
convulsions,
crystalluria,
toxic nephrosis,
headache, peripheral
neuritis, urticaria, cough
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Beta-Lactam Antibiotics




Penicillins
Cephalosporins
Carbapenems
Monobactams
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Penicillins




Natural penicillins
Penicillinase-resistant penicillins
Aminopenicillins
Extended-spectrum penicillins
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Penicillins (cont’d)

Natural penicillins



penicillin G
penicillin V
Penicillinase-resistant drugs




nafcillin
cloxacillin
oxacillin
dicloxacillin
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Penicillins (cont’d)

Aminopenicillins


amoxicillin (Amoxil), ampicillin (generic only)
Extended-spectrum drugs

carbenicillin
 piperacillin
 ticarcillin
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Penicillins: Mechanism of Action





Penicillins enter the bacteria via the cell wall
Inside the cell they bind to penicillin-binding
protein
Once bound, normal cell wall synthesis is
disrupted
Result: bacteria cells die from cell lysis
Penicillins do not kill other cells in the body
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Penicillins: Indications

Prevention and treatment of infections caused
by susceptible bacteria, such as:

Gram-positive bacteria, including Streptococcus spp.,
Enterococcus spp., Staphylococcus spp.
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Penicillins: Adverse Effects

Allergic reactions to the penicillins occur in 0.7%
to 4% of treatment courses



Urticaria, pruritus, angioedema
Those allergic to penicillins have an increased
risk of allergy to other beta-lactam antibiotics
Only those patients with a history of throat
swelling or hives from penicillin should not
receive cephalosporins
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Penicillins: Adverse Effects (cont’d)

Common adverse effects


Nausea, vomiting, diarrhea, abdominal pain
Other adverse effects are less common
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Penicillins: Interactions

MANY interactions!

NSAIDs
 Oral contraceptives
 Warfarin
 Others
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Classroom Response Question
A patient is receiving Augmentin (amoxicillin and
clavulanic acid) liquid solution through a PEG tube.
What is the purpose of the clavulanic acid?
A. It works synergistically with the antibiotic to
improve potency.
B. It inhibits the action of the enzymes produced by
beta-lactamase–producing bacteria.
C. It protects the antibiotic from the harmful gastric
acid secretions in the stomach.
D. It enhances the absorption of the antibiotic in the
small intestine.
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Cephalosporins





First generation
Second generation
Third generation
Fourth generation
Fifth generation
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Cephalosporins (cont’d)





Semisynthetic antibiotics
Structurally and pharmacologically related
to penicillins
Bactericidal action
Broad spectrum
Divided into groups according to their
antimicrobial activity
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Cephalosporins:
First Generation




Good gram-positive coverage
Poor gram-negative coverage
Parenteral and PO forms
Examples

cefadroxil (Duricef, Ultracef)
 cephradine (Velosef)
 cefazolin (Ancef)
 cephalexin (Keflex)
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Cephalosporins:
First Generation (cont’d)

Used for surgical prophylaxis, and for
susceptible staphylococcal infections


cefazolin (Ancef and Kefzol): IV or IM
cephalexin (Keflex): PO
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Cephalosporins:
Second Generation



Good gram-positive coverage
Better gram-negative coverage than first
generation
Examples:

cefaclor (Ceclor)
 cefprozil (Cefzil)
 cefoxitin (Mefoxin)
 cefuroxime (Zinacef)
 cefotetan (Cefotan)
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Cephalosporins:
Second Generation (cont’d)

cefoxitin (Mefoxin): IV and IM



Used prophylactically for abdominal or colorectal
surgeries
Also kills anaerobes
cefuroxime



Zinacef is parenteral form; Ceftin is PO
Surgical prophylaxis
Does not kill anaerobes
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Cephalosporins:
Third Generation



Most potent group against gram-negative
bacteria
Less active against gram-positive bacteria
Examples

cefotaxime (Claforan)
 ceftazidime (Fortaz)
 cefdinir (Omnicef)
 ceftizoxime (Cefizox)
 ceftriaxone (Rocephin)
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Cephalosporins:
Third Generation (cont’d)

ceftriaxone (Rocephin)



IV and IM, long half-life, once-a-day dosing
Elimination is primarily hepatic
Easily passes meninges and diffused into CSF to
treat CNS infections
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Cephalosporins:
Third Generation (cont’d)

ceftazidime (Ceptaz, Fortaz, Tazidime)





IV and IM forms
Excellent gram-negative coverage
Used for difficult-to-treat organisms such as
Pseudomonas spp.
Excellent spectrum of coverage
Resistance is limiting usefulness
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Cephalosporins:
Fourth Generation


Broader spectrum of antibacterial activity than
third generation, especially against grampositive bacteria
Uncomplicated and complicated UTI

cefepime (Maxipime)
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Cephalosporins:
Fifth Generation

ceftaroline (Teflaro)


Broader spectrum of antibacterial activity
Effective against a wide variety of organisms
• MRSA
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Cephalosporins:
Adverse Effects

Similar to penicillins


Mild diarrhea, abdominal cramps, rash, pruritus,
redness, edema
Potential cross-sensitivity with penicillins if
allergies exist
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Carbapenems



Broadest antibacterial action of any antibiotics to
date
Reserved for complicated body cavity and
connective tissue infections in acutely ill
hospitalized patients
May cause drug-induced seizure activity

This risk can be reduced with proper dosage
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Carbapenems

imipenem/cilastatin (Primaxin)





Used for treatment of bone, joint, skin, and soft-tissue
infections; many other uses
Cilastatin inhibits an enzyme that breaks down
imipenem
meropenem (Merrem)
ertapenem (Invanz)
doripenem (Doribax)
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Monobactams

aztreonam (Azactam)

Synthetic beta-lactam antibiotic
 Primarily active against aerobic gram-negative
bacteria (E. coli, Klebsiella spp., Pseudomonas spp.)
 Bactericidal
 Parenteral use only
 Used for moderately severe systemic infections and
UTIs
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Macrolides



erythromycin (E-mycin, E.E.S, others)
azithromycin (Zithromax)
clarithromycin (Biaxin)
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Macrolides:
Mechanism of Action




Prevent protein synthesis within bacterial cells
Considered bacteriostatic
Bacteria will eventually die
In high enough concentrations, may also be
bactericidal
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Macrolides: Indications

Strep infections


Mild to moderate URI and LRI


Haemophilus influenzae
Spirochetal infections


Streptococcus pyogenes (group A beta-hemolytic
streptococci)
Syphilis and Lyme disease
Gonorrhea, Chlamydia, Mycoplasma
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Macrolides: Indications (cont’d)

azithromycin and clarithromycin


Approved for Mycobacterium avium-intracellulare
complex infection (opportunistic infection associated
with HIV/AIDS)
clarithromycin

Recently approved for use in combination with
omeprazole for treatment of active ulcer disease
associated with Helicobacter pylori infection
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Macrolides: Adverse Effects

GI effects, primarily with erythromycin


Nausea, vomiting, diarrhea, hepatotoxicity, flatulence,
jaundice, anorexia
Azithromycin and clarithromycin: fewer GI
adverse effects, longer duration of action, better
efficacy, better tissue penetration
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Ketolide

telithromycin (Ketek)

Only drug in this class
 Better antibacterial coverage than macrolides
 Associated with severe liver disease
 Use is limited
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Tetracyclines






demeclocycline (Declomycin)
oxytetracycline (Terramycin)
tetracycline
doxycycline (Doryx, Vibramycin)
minocycline (Minocin)
tigecycline (Tygacil)
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Tetracyclines (cont’d)





Natural and semisynthetic
Obtained from cultures of Streptomyces
Bacteriostatic—inhibit bacterial growth
Inhibit protein synthesis
Stop many essential functions of the bacteria
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Tetracyclines (cont’d)



Bind (chelate) to Ca+++ and Mg++ and Al+++ ions
to form insoluble complexes
Dairy products, antacids, and iron
salts reduce oral absorption of tetracyclines
Should not be used in children under age 8 or in
pregnant/lactating women because tooth
discoloration will occur if the drug binds to the
calcium in the teeth
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Tetracyclines: Indications

Wide spectrum


Gram-negative and gram-positive organisms,
protozoa, Mycoplasma, Rickettsia, Chlamydia,
syphilis, Lyme disease, acne, others
Demeclocycline is also used to treat SIADH by
inhibiting the action of ADH
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Tetracyclines: Adverse Effects

Strong affinity for calcium


Discoloration of permanent teeth and tooth
enamel in fetuses and children, or nursing infants if
taken by the mother
May retard fetal skeletal development if taken during
pregnancy
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Tetracyclines: Adverse Effects
(cont’d)

Alteration in intestinal flora may result in:

Superinfection (overgrowth of nonsusceptible
organisms such as Candida)
 Diarrhea
 Pseudomembranous colitis
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Tetracyclines: Adverse Effects
(cont’d)

May also cause:

Vaginal candidiasis
 Gastric upset
 Enterocolitis
 Maculopapular rash
 Other effects
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Nursing Implications




Before beginning therapy, assess drug allergies;
renal, liver, and cardiac function; and other lab
studies
Be sure to obtain thorough patient health history,
including immune status
Assess for conditions that may be
contraindications to antibiotic use or that may
indicate cautious use
Assess for potential drug interactions
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Nursing Implications (cont’d)

It is ESSENTIAL to obtain cultures from
appropriate sites BEFORE beginning antibiotic
therapy
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Nursing Implications (cont’d)


Instruct patients to take antibiotics exactly as
prescribed and for the length of time prescribed;
they should not stop taking the medication early
when they feel better
Assess for signs and symptoms of
superinfection: fever, perineal itching, cough,
lethargy, or any unusual discharge
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Nursing Implications (cont’d)

For safety reasons, check the name of the
medication carefully because there are many
drugs that sound alike or have similar spellings
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Classroom Response Question
When completing an admission assessment, the
patient states that she is allergic to sulfa drugs.
What will the nurse do next?
A. Mark the allergy on her medical record.
B. Place an “allergy” armband on the patient.
C. Ask the patient for more information about the
allergic reaction she had.
D. Notify the physician about the patient’s allergy.
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Nursing Implications (cont’d)



Each class of antibiotics has specific adverse
effects and drug interactions that must be
carefully assessed and monitored
The most common adverse effects of antibiotics
are nausea, vomiting, and diarrhea
All oral antibiotics are absorbed better if taken
with at least 6 to 8 ounces of water
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Classroom Response Question
A patient has a prescription for a sulfa drug as treatment for
a urinary tract infection. She is also taking an oral
contraceptive, an oral sulfonylurea antidiabetic drug, and
phenytoin for a history of seizures. Which drug may pose a
potential serious interaction with the sulfa drug?
A. The oral contraceptive
B. The oral antidiabetic drug
C. The phenytoin
D. All of these
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Nursing Implications (cont’d)

Sulfonamides



Take with 2000 to 3000 mL of fluid/24 hr
Assess RBCs prior to beginning therapy
Take oral doses with food
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Nursing Implications (cont’d)

Penicillins


Take oral doses with water (not juices) as acidic fluids
may nullify drug’s antibacterial action
Monitor patients taking penicillin for an allergic
reaction for at least 30 minutes after administration
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Nursing Implications (cont’d)

Cephalosporins

Assess for penicillin allergy; may have cross allergy
 Give orally administered forms with food to decrease
GI upset, even though this will delay absorption
 Some of these drugs may cause a disulfiram
(Antabuse)-like reaction when taken with alcohol
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Nursing Implications (cont’d)

Macrolides


These drugs are highly protein-bound and will cause
severe interactions with other protein-bound drugs
The absorption of oral erythromycin is enhanced
when taken on an empty stomach, but because of the
high incidence of GI upset, many drugs are taken
after a meal or snack
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Nursing Implications (cont’d)

Tetracyclines



Avoid milk products, iron preparations, antacids, and
other dairy products because of the chelation and
drug-binding that occurs
Take all medications with 6 to 8 ounces of fluid,
preferably water
Because of photosensitivity, avoid sunlight and
tanning beds
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Nursing Implications (cont’d)

Monitor for therapeutic effects

Improvement of signs and symptoms of infection
 Return to normal vital signs
 Negative culture and sensitivity tests
 Disappearance of fever, lethargy, drainage, and
redness

Monitor for adverse reactions
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