CHAPTER 39
Antibiotics Part 2
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Antibiotic Therapy: Concepts
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Multidrug resistance
Therapeutic drug monitoring
Minimum inhibitory concentration (MIC)
Time-dependent killing
Concentration-dependent killing
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Once-daily dosing vs. multi-daily dosing
Peak and trough blood levels
Synergistic effects
Post-antibiotic effect (PAE)
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Antibiotic Therapy: Toxicities
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Ototoxicity
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Nephrotoxicity
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Temporary or permanent hearing loss, balance problems
Varying degrees of reduced renal function
Rising serum creatinine may indicate reduced creatinine
clearance
Monitor trough levels every 5 to 7 days while on
therapy or as ordered
Monitor serum creatinine levels at least every 3 days
as an index of renal function
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Aminoglycosides
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gentamicin (Garamycin)
neomycin (Neo-fradin)
tobramycin (Nebcin)
amikacin (Amikin)
kanamycin
streptomycin
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Aminoglycosides (cont’d)
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Natural and semisynthetic
Produced from Streptomyces
Poor oral absorption; no PO forms
Very potent antibiotics with serious toxicities
Bactericidal; prevent protein synthesis
Kill mostly gram-negative bacteria; some
gram-positive also
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Aminoglycosides: Indications
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Used to kill gram-negative bacteria such as
Pseudomonas spp., E. coli, Proteus spp.,
Klebsiella spp., Serratia spp.
Often used in combination with other
antibiotics for synergistic effects
Used for certain gram-positive infections
that are resistant to other antibiotics
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Aminoglycosides:
Indications (cont’d)
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Aminoglycosides are poorly absorbed
through the GI tract, and given parenterally
Exception: neomycin
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Given orally to decontaminate the GI tract before
surgical procedures
Also used as an enema for this purpose
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Aminoglycosides:
Adverse Effects
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Cause serious toxicities
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Nephrotoxicity (renal damage)
Ototoxicity (auditory impairment and vestibular
impairment [eighth cranial nerve])
Must monitor drug levels to prevent toxicities
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Aminoglycosides:
Adverse Effects (cont’d)
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Ototoxicity and nephrotoxicity are
the most significant
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Headache
 Paresthesia
 Fever
 Superinfections
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Vertigo
 Skin rash
 Dizziness
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Quinolones
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ciprofloxacin (Cipro)
norfloxacin (Noroxin)
levofloxacin (Levaquin)
moxifloxacin (Avelox)
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Quinolones (cont’d)
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Also called “fluoroquinolones”
Excellent oral absorption
Absorption reduced by antacids
Effective against gram-negative organisms
and some gram-positive organisms
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Quinolones:
Mechanism of Action
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Bactericidal
Alter DNA of bacteria, causing death
Do not affect human DNA
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Quinolones: Indications
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Gram-negative bacteria such as
pseudomonas
Respiratory infections
Bone and joint infections
GI infections
Skin infections
Sexually transmitted diseases
Anthrax
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Fluoroquinolones:
Adverse Effects
Body System
CNS
GI
Cardiac
Adverse Effects
Headache, dizziness, fatigue,
depression, restlessness,
insomnia
Nausea, vomiting, diarrhea,
constipation, thrush, increased
liver function studies, others
Prolonged QT interval
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Fluoroquinolones:
Adverse Effects (cont’d)
Body System
Integumentary
Other
Adverse Effects
Rash, pruritus, urticaria,
flushing, photosensitivity
(with lomefloxacin)
Fever, chills, blurred vision,
tinnitus
Black box warning: increased risk of tendonitis and
tendon rupture
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Other Antibiotics
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clindamycin (Cleocin)
linezolid (Zyvox)
metronidazole (Flagyl)
nitrofurantoin (Macrodantin)
quinupristin and Dalfopristin (Synercid)
daptomycin (Cubicin)
vancomycin (Vancocin)
colistimethate (Coly-mycin)
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Other Antibiotics (cont’d)
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clindamycin (Cleocin)
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Used for chronic bone infections, GU infections,
intraabdominal infections, other serious infections
May cause pseudomembranous colitis
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Other Antibiotics (cont’d)
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linezolid (Zyvox)
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New class: oxazolidinones
Used to treat vancomycin-resistant Enterococcus
faecium (VREF, VRE), hospital-acquired skin and
skin structure infections, including those with
MRSA
May cause hypotension, serotonin syndrome if
taken with SSRIs, and reactions if taken with
tyramine-containing foods
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Other Antibiotics (cont’d)
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metronidazole (Flagyl)
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Used for anaerobic organisms
Intraabdominal and gynecologic infections
Protozoal infections
Several drug interactions
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Other Antibiotics (cont’d)
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nitrofurantoin (Macrodantin)
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Primarily used for UTIs (E. coli, S. aureus,
Klebsiella spp., Enterobacter spp.)
 Use carefully if renal function is impaired
 Drug concentrates in the urine
 May cause fatal hepatotoxicity
 Usually well-tolerated if patient is kept wellhydrated
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Other Antibiotics (cont’d)
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quinupristin and dalfopristin (Synercid)
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30:70 combination, work synergistically
Used for bacteremia and infections caused by
vancomycin-resistant Enterococcus (VRE) and
other complicated skin infections
May cause arthralgias, myalgias
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Other Antibiotics (cont’d)
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daptomycin (Cubicin)
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New class: lipopeptide
Used to treat complicated skin and
soft-tissue infections
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Other Antibiotics (cont’d)
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vancomycin (Vancocin)
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Natural, bactericidal antibiotic
Destroys cell wall
Treatment of choice for MRSA and other
gram-positive infections
Must monitor blood levels to ensure therapeutic
levels and prevent toxicity
May cause ototoxicity and nephrotoxicity
Should be infused over 60 minutes
Rapid infusions may cause hypotension
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Other Antibiotics (cont’d)
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vancomycin (Vancocin) (cont’d)
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Monitor IV site closely
Red man syndrome may occur
• Flushing/itching of head, neck, face, upper
trunk
• Antihistamine may be ordered to reduce these
effects
Ensure adequate hydration (2 L fluids/24 hr) if not
contraindicated to prevent nephrotoxicity
Monitor trough levels carefully
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Nursing Implications
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Before beginning therapy, assess drug
allergies; hepatic, renal, 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)
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It is ESSENTIAL to obtain cultures from
appropriate sites BEFORE beginning
antibiotic therapy
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
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Nursing Implications (cont’d)
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Assess for signs and symptoms of
superinfection: fever, perineal itching, cough,
lethargy, or any unusual discharge
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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Nursing Implications (cont’d)
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Each class of antibiotics has specific adverse
effects and drug interactions that must be
carefully assessed and monitored
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Nursing Implications (cont’d)
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Aminoglycosides
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Monitor peak and trough blood levels of these
drugs to prevent nephrotoxicity and ototoxicity
 Symptoms of ototoxicity include dizziness, tinnitus,
and hearing loss
 Symptoms of nephrotoxicity include urinary casts,
proteinuria, and increased BUN and serum
creatinine levels
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Nursing Implications (cont’d)
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Monitor for therapeutic effects
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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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