ANTIMICROBIAL

AGENTS
TOPICS:
❑ Classification of Antimicrobial Drugs
✔ Classification by Susceptible Organism
✔ Classification by Mechanism of Action

❑ Acquired Resistance to Antimicrobial Drugs

❑ Superinfection
❑ Nursing responsibilities
❑ Antibiotic Classifications
❑ Antifungal, Antiprotozoal and Antihelmenthics
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BASIC PRINCIPLES OF
ANTIMICROBIAL THERAPY
 Modern antimicrobial agents had their debut in the
1930s and 1940s and have greatly reduced morbidity
and mortality from infection. As newer drugs are
introduced, our ability to fight infections increases
even more. However, despite impressive advances,
continued progress is needed. There remain organisms
that respond poorly to available drugs; there are
effective drugs whose use is limited by toxicity; and
there is, because of evolving microbial resistance, the
constant threat that currently effective antibiotics will
be rendered useless.

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 Antibiotic and
Antimicrobial drug are
used interchangeably.
However, be aware that
the formal definitions of
these words are not
identical.
an ANTIBIOTIC is a chemical that is
produced by one microbe and has
the ability to harm other microbes.
Under this definition, only those
compounds that are actually made
by microorganisms qualify as
antibiotics.

an ANTIMICROBIAL drug is defined

as any agent, natural or synthetic,
that has the ability to kill or
suppress microorganisms. Under
this definition, no distinction is
made between compounds
produced by microbes and those
 From the perspective of
therapeutics, there is no
benefit to distinguishing
between drugs made by
microorganisms and drugs
made by chemists. Hence, the
current practice is to use the
terms antibiotic and
antimicrobial drug
interchangeably.
ACTIONS OF ANTIMICROBIAL DRUGS

▸ The primary goal of antimicrobial therapy is to assist the

body’s defenses in eliminating a pathogen.
▸ Medications that accomplish this goal by killing bacteria
are called bacteriocidal.
▸ Some drugs do not kill the bacteria but instead slow their
growth, allowing the body’s natural defenses to eliminate
the microorganisms. These growth-slowing drugs are called
bacteriostatic.
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EMPIRIC ANTIMICROBIAL THERAPY
Empiric antimicrobial therapy is directed against
an anticipated and likely cause of infectious
disease. It is used when antimicrobials are given to
a person before the specific bacterium or fungus
causing an infection is known.

It is the initial antibiotic regimen started within 24

hours of admission. 
antibiotic selection: using observations of the
patient (history, physical examination and
laboratory test results) along with past clinical
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experiences and the medical literature.
CLASSIFICATION OF ANTIMICROBIAL
DRUGS

▸ Classification by Susceptible
Organism
▸ Classification by Mechanism of
Action
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Classification by Susceptible Organism

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ANTIBIOTICS DIFFER WIDELY IN THEIR
ANTIMICROBIAL ACTIVITY.

▸ Narrow-spectrum ▸ Broad-spectrum
antibiotics, are antibiotics are
active against only a active against a
few species of wide variety of
microorganisms. microbes.

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Classification by Mechanism of Action
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THE ANTIMICROBIAL DRUGS FALL INTO SEVEN MAJOR GROUPS
BASED ON MECHANISM OF ACTION.

1. Inhibitors of cell wall synthesis

2. Drugs that disrupt the cell membrane
3. Bactericidal inhibitors of protein synthesis
4. Bacteriostatic inhibitors of protein synthesis
5. Drugs that interfere with synthesis or integrity of bacterial DNA and
RNA
6. Antimetabolites
7. Drugs that suppress viral replication

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 Selection of an Effective
Antibiotic
• Selecting an incorrect drug will delay proper treatment, giving the microorganisms more time to invade.
• Prescribing ineffective antibiotics also promotes the development of resistance and may cause
unnecessary adverse effects in the patient.
• Ideally, laboratory tests should be conducted to identify the specific pathogen prior to beginning
anti-infective therapy. Laboratory tests may include examination of urine, stool, spinal fluid, sputum,
blood, or purulent drainage for microorganisms.
• Organisms isolated from the specimens are grown in the laboratory and identified. After identification,
the laboratory tests different antibiotics to determine which is most effective against the infecting
microorganism. This process of growing the pathogen and identifying the most effective antibiotic is
called culture and sensitivity (C&S) testing.
 ACQUIRED RESISTANCE TO ANTIMICROBIAL
Over time, an organism that hadDRUGS
once been
highly sensitive to an antibiotic may become
less susceptible, or it may lose drug sensitivity
entirely. In some cases, resistance develops to
several drugs. Acquired resistance is of great
concern in that it can render currently
effective drugs useless, thereby creating a
clinical crisis and a constant need for new
antimicrobial agents. As a rule, antibiotic
resistance is associated with extended
hospitalization, significant morbidity, and
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excess mortality.
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recall two aspects of microbial ecology:
(1) microbes secrete compounds that
are toxic to other microbes and (2)
microbes within a given ecologic niche
(e.g., large intestine, urogenital tract,
skin) compete with each other for
available nutrients. How Do
▸ Under drug-free conditions, the Antibiotics
various microbes in a given niche
keep each other in check.
Promote
▸ Furthermore, if none of these Resistance?
organisms is drug resistant,
introduction of antibiotics will be
equally detrimental to all members of 20
the population and therefore will not
promote the growth of any individual
 present, antibiotics will create selection
pressure favoring its growth by killing off
sensitive organisms.

▸ In doing so, the drug will eliminate the

toxins they produce and will thereby
facilitate survival of the microbe that is
drug resistant. How Do
▸ Also, elimination of sensitive organisms Antibiotics
will remove competition for available
nutrients, thereby making conditions
Promote
even more favorable for the resistant Resistance?
microbe to flourish.

▸ Hence, although drug resistance is of no

benefit to an organism when there are
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no antibiotics present, when antibiotics
are introduced, they create selection
ALL antimicrobial drugs
promote the emergence of
drug-resistant organisms.
However, some agents are
more likely to promote
Which
resistance than others.
Antibiotics
Because broad-spectrum
antibiotics kill more competing
Promote
organisms than do
Resistance?
narrow-spectrum drugs,
broad-spectrum agents do the
most to facilitate emergence
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of resistance.
During antibiotic therapy, a nurse
should…
Monitor SUPERINFECTIONS
E valuate liver / renal functions
D iarrhea (GI DISTRESS:N/V/D/C), may be common, provide health teachings
I nform the patient to consult prior to taking other meds
C ultures prior to initial dose (ideally)
Ask about Allergy and alcohol is No - no
T each patient that antibiotic are to be taken on full course
E valuate cultures, temperature and lab results
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SUPERINFECTION

Superinfection is a special
example of the emergence
of drug resistance. A
superinfection is defined
as a new infection that
appears during the course
of treatment for a primary
infection.
 SUPERINFECTION

It can occur in the mouth,

respiratory tract, intestine,
genitourinary tract,
or skin. • Fatigue or weakness
• New
or increased heat, pain, redness,
swelling, or unusual drainage in any
area.
more common with the • Development or worsening of lesions
or ulceration of oral mucous
use of broad-spectrum membrane, presence of a black furry
tongue.
antibiotics. • New or increased episodes
of diarrhea and abdominal
cramping or pain
General Nursing
Responsibility
▸ Check for antibiotic allergy
▸ Administer antibiotics only as ordered
▸ Regularly check for organ toxicity
▸ Educate patients never to take antibiotics
without guidance
from a licensed doctor
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 ANTIBIOTIC CLASSIFICATIONS

Penicillins Cephalosporins Macrolides

Tetracyclines Aminoglycosides Flouroquinolones Sulfonamides

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PENICILLIN Nomenclature: usually ends in “-cillins”
Known Drug: pen g (iv form), pen v (oral form),
amoxicillin
Action: bactericidal, inhibit cell wall synthesis
(beta-lactam ring)
Indication: most gram (+) and some gram (-)
bacteria
• Pneumonia, rti, uti, sti, some skin infections
• Meningitis, GI infections due to salmonella
and shigella
Warnings: allergy to penicillin and
cephalosphorins, caution with renal and liver
failure
side effects: Nausea, vomiting, diarrhea
watch out for: allergy and superinfection,
haemolytic anemia
Note: bacterial evolution had enable some
bacteria to resist penicillin by releasing
penicillinase and beta-lamases
 Further Note:
PENICILLIN Broad-spectrum penicillins (aminopenicillins)
• Prototype: amoxillin, ampicillin (se: rash,
pseudomembranous colitis)
Penicillinase-resistant penicillins
(antistaphyloccoal penicillins)
• Prototype: methicillin (se: interstitial nephritis)
• Not used for mrsa
Extended-spectrum penicillins
(antipseudomonal penicllins)
• Used w/th clavunalic acid
• Ticarcillin , carbenicillin, pipercillin
Beta-lactamase inhibitors
• amoxicillin- clavulanic acid
• ampicillin-sulbactam (Unasyn),
• piperacillin-tazobactam (vigocid)
• Ticarcillin- clavulanic acid (triclav)
PENICILLIN
Drug interactions:
• may decrease the
effectiveness of oral
contraceptives
• IF mixed with an
aminoglycoside in IV solution,
the actions of both drugs are
inactivated.
Cephalosporin
 Nomenclature: usually STARTS in “Cef-”
CEPHALEXIN Known Drug: cephalexin, ceftriaxone
Action: bactericidal, inhibit cell wall
synthesis, resistant to beta-lactamase
Indication: gram (+) and (-) bacteria

1st gen – 2nd choice if (+) penicillin-allergy,

mostly gram (+) however often destroyed by
beta-lactamase (cephalexin, cefazolin)
2nd gen – usually gram (-) bacteria, most are
not affected by beta-lactamase (cefaclor,
cefoxitin, cefuroxime)
3rd gen and 4th gen - effective in treating
sepsis and many strains of gram-negative
bacilli
CEPHALEXIN 3rd gen – cefixime, cefoxatime, ceftazidime, ceftriaxone
4th gen – cefipime

WARNING: allergy to penicillin and cephalosphorins

Side effects: GI disturbance (n/v/d)
• Increase in glucose values
• Anaphylaxis may occur
• Nephrotoxic
• Thromobocytopenia
Drug interactions: No-No to alcohol
(results to disulfram-reaction: flushing of the skin,
accelerated heart rate, shortness of breath, nausea,
vomiting, throbbing headache, visual disturbance, mental
confusion, postural syncope, and circulatory collapse
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*Methicillin-resistant Staphylococcus
aureus (MRSA) is a bacterium that
causes infections in different parts of
the body. MRSA infection is caused by
a type of staph bacteria that's become
resistant to many of the antibiotics used
to treat ordinary staph infections.

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Macrolide
MACROLIDE Nomenclature: has “-thromycin” but pls
remember ace
Known Drug: Azithromycin, Clarithromycin,
Erythromycin
Action: bacteriostatic, inhibit protein
synthesis
Indication: gram (+) and (-) bacteria
• mild to moderate RTI, INFECTION OF
sinuses, GI tract, skin and soft tissue,
diphtheria, impetigo contagiosa, and STI
Warnings: allergy to MACROLIDES caution
with renal and liver functions
side effects: Nausea, vomiting, diarrhea,
AnD CRAMPING, POSSIBLY CONJUCTIVITIS
(AZITH), arrhythmia (erythromycin)
MACROLIDE
Watch for: signs of SUPERINFECTION

DRUG INTERACTION:
• can increase serum levels of theophylline
(bronchodilator),
• To avoid severe toxic effects,
erythromycin should not be used with
other macrolides
• Antacids may reduce azithromycin peak
levels when taken at the same time
LINCOSAMIDES
GLYCOPEPTIDES

Extended-Macrolide Group

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 Nomenclature: NONE
EXTENDED-MACROLIDE GROUP: Known Drug: Clindamycin
Action: Bacteriostatic, inhibit RNA
LINCOSAMIDES TRANSLOCATION, may also have bactericidal
effect
Indication: ANAEROBIC INFECTIONS ABOVE
THE DIAPHRAGM
• Lung abscess
• Aspiration pneumonia
• Mrsa soft tissue infections
• Necrotizing fasciitis
• PID (Pelvic Inflammatory Disease)
Side effects: Nausea, vomiting, stomatitis,
rash
Adverse effects: colitis and anaphylactic
shock.
Drug interactions: incompatible with
aminophylline, phenytoin (Dilantin),
barbiturates, and ampicillin
 Nomenclature: NONE
EXTENDED-MACROLIDE GROUP: Known Drug: vancomycin
Action: bactericidal, inhibit cell wall synthesis

GLYCOPEPTIDES Indication: gram (+) infections

• Antibiotic-associated
caused by clostridium
pseudomembranous
difficile and
staphylococcal enterocolitis
• used against drug-resistant S.aureus
• cardiac surgical prophylaxis for individuals with
penicillin allergies
• given IV for severe infections due to MRSA;
septicemia; and bone, skin, and lower respiratory
tract infections that do not respond or are
resistant to other antibiotics.
Side effects: Nausea, vomiting, taste alterations,
“red-man syndrome”
Adverse effects: ototoxic, nephrotoxic,
thrombophlebitis
Drug interactions: not to be given with furosemide,
aminoglycosides, cisplatin, and cyclosporine
Tetracycline
TETRACYCLINES Nomenclature: usually ends in “-cycline”
Known Drug: doxycycline, tetracycline
Action: bactericiostatic, inhibit protein
synthesis
Indication: gram (+) aerobes and
anaearobes
Useful in skin infections, STIs,
Side effects: nausea, vomiting, diarrhea,
photosensitivity, dental staining
Adverse effects: nephrotoxic,
superinfection
Not for: pregnant and lactating moms and
children < 8years old
Drug interactions: not to be given antacids
Aminoglycosides
AMINOGLYCLOSIDES
Nomenclature: usually has “-mycin”
Known Drug: gentamycin,
streptomycin, amikacin
Action: bactericidal, inhibit protein
synthesis
Indication: serious gram (+) and (-)
infection
• Useful against MRSA
Side effects: nausea, vomiting, tinnitus
Adverse effects: nephrotoxic, ototoxic,
neurotoxic, superinfection
Drug interactions: not to be given with
penicillin and coumadin
Fluoroquinolones
FLUOROQUINOLONES
Nomenclature: usually ends in “-floxacin”
Known Drug: ciprofloxacin, ofloxacin,
levofloxacin
Action: bactericidal, inhibit dna synthesis
Indication: SOME gram (+) and (-) infection
• Useful against UTI, BRONCHITIS, STI, BONE,
JOINT, OTIC AND OPTHALMIC INFECTION
Side effects: nausea, vomiting,
diarrhea/constipation, photosensitivity, rupture
of achilles tendon
Adverse effects: nephrotoxic, thrombophlebitis,
superinfection
Not for: PREGNANT AND LACTATING MOTHERS,
PATIENT WITH MYASTHENIA GRAVIS
Drug interactions: not to be taken with antacids
and iron
Sulfonamides
SULFONAMIDES Nomenclature: usually starts in “sulfa-”
Known Drug: sulfadiazine, trimethoprim-sulfa
methoxazole
Action: bactericiostatic, inhibit folic acid
synthesis
Indication: may be used as alternarive for
patients with penicillin allergy
• gram (+) and (-) infection
• Useful against UTI, rti, ear and GI infection
• used to prevent Pneumocystis carinii in
patients with AIDS
Side effects: nausea, vomiting, ANOREXIA,
ANEMIA, RASH, PHOTOSENSITIVY,
CRYSTALLURIA
Adverse effects: nephrotoxic, BLOOD
DYSCRASIA, STEVEN JOHNSONS’
SYNDROME
Antifungals and
Antiprotozoals
ANTIFUNGALS • FUNGUS – ALSO KNOWN AS DERMATOPHYTES
• MYCOSIS – INFECTION CAUSED BY FUNGUS
• USUALLY AFFECT THE INTEGUMENTARY
SYSTEM

• CLASSIFIED IN 2 TYPES:
• OPPURTUNISTIC

• NONOPPURTUNISTIC

ANTIFUNGALS / ANTIMYCOTIC

• POLYENES (E.G., AMPHOTERICIN B,

NYSTATIN)
 POLYENES • NOMENCLATURE: NONE
AMPHOTERICIN B • KNOWN DRUG: FUNGIZONE
• ACTION: FUNGICIDAL, BINDS TO THE
FUNGAL CELL MEMBRANE AND FORMING
OPEN CHANNELS THAT INCREASE CELL
PERMEABILITY AND LEAKAGE OF
INTRACELLULAR COMPONENTS

• INDICATION: SEVERE SYSTEMIC FUNGAL

INFECTION

• SIDE EFFECTS: FLUSH, FEVER, CHILLS,

NAUSEA, VOMITING, HYPOTENSION,
POLYENES • NOMENCLATURE: NONE
NYSTATIN • KNOWN DRUG: MYCOSTATIN
• ACTION: FUNGISTATIC, FUNGICIDAL,
INCREASES PERMEABILITY OF THE
FUNGAL CELL MEMBRANE, THUS
CAUSING THE FUNGAL CELL TO
BECOME UNSTABLE AND TO
DISCHARGE ITS CONTENT.

• INDICATION: TOPICAL AND ORAL

TREATMENT FOR CANDIDA INFECTION
 • NOMENCLATURE: ENDS IN “-AZOLE”
AZOLE GROUP
• KNOWN DRUG: KETOCONAZOLE,
METRONIDAZOLE, FLUCONAZOLE

• ACTION: FUNGICIDAL, INHIBIT

CYTOCHROME P450 IN FUNGAL
CELLS LEADING TO CELL LYSIS

• INDICATION: TOPICAL AND ORAL

TREATMENT FOR VARIOUS FUNGAL
INFECTIONS

• SIDE EFFECTS: NAUSEA, VOMITING,

METRONIDAZOLE • DRUG CLASS: ANTIFUNGAL,
ANTIPROTOZOAL, AMOEBICIDE,
ANTIBACTERIAL

• ACTION: INHIBIT DNA SYNTHESIS

RESULTING TO CELL DEATH

• INDICATION: H. PYLORI INFECTION,

AMOEBIASIS, TRICHOMINIASIS, FUNGAL
INFECTIONS

• SIDE EFFECTS: NAUSEA, VOMITING,

DIARRHEA, UNPLEASANT METALLIC
TASTE
Antihelmenthics
ANTIHELMINTHS helminths – large organisms (parasitic
worms) that feed on host tissue.
helminthiasis – INFECTION CAUSED
BY helminths
• USUALLY AFFECT THE intestines
but may extend to the lymphatic
system, blood vessels and liver
Group of helminths
• cestodes (tapeworms)
• trematodes (flukes)
• intestinal nematodes (roundworms)
• tissue-invading nematodes (tissue
roundworms and filariae)
 Nomenclature: NONE
ALBENDAZOLE Known Drug: ALBENDAZOLE (TAPE
WORM), MEBENDAZOLE (PIN WORM)
PRAZIQUANTEL (SCHISTOSOMIASIS)
PYRANTEL (ASCARIS)
Action: UNCLEAR BUT generally involves
interference with the integrity of parasite
cells, neuromuscular coordination, or
protective mechanisms against host
immunity, which lead to starvation,
paralysis, and expulsion or digestion of the
parasite.
Indication: HELMENTHIC INFECTION
Side effects: GI DISTRESS, POSSIBLY
DIZZINESS, WEAKNESS, HEADACHE,
DROWSINESS
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