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CLINICAL
PHARMACOLOGY OF
ANTIBACTERIAL AGENTS
Actions of antibacterial drugs on
bacterial cells
Mechanisms of Action
1. Inhibition of bacterial cell wall synthesis or activation of enzymes that
disrupt bacterial cell walls (eg, penicillins, cephalosporins,
vancomycin)
2. Inhibition of protein synthesis by bacteria or production of abnormal
bacterial proteins (eg, aminoglycosides, clindamycin, erythromycin,
tetracyclines). These drugs bind irreversibly to bacterial ribosomes,
intracellular structures that synthesize proteins. When antimicrobial
drugs are bound to the ribosomes, bacteria cannot synthesize the
proteins necessary for cell walls and other structures.
3. Disruption of microbial cell membranes (eg, antifungals)
4. Inhibition of organism reproduction by interfering with nucleic acid
synthesis (eg, fluoroquinolones, rifampin, anti–acquired
immunodeficiency syndrome antivirals)
5. Inhibition of cell metabolism and growth (eg, sulfonamides,
trimethoprim)
Antibiotic Combination Therapy
Antimicrobial drugs are often used in combination.
Indications for combination therapy may include:
• Infections caused by multiple microorganisms (eg,
abdominal and pelvic infections)
• Nosocomial infections, which may be caused by many
different organisms
• Serious infections in which a combination is synergistic
(eg, an aminoglycoside and an antipseudomonal
penicillin for pseudomonal infections)
• Likely emergence of drug-resistant organisms if a single
drug is used (eg, tuberculosis). Although drug
combinations to prevent resistance are widely used, the
only clearly effective use is for treatment of tuberculosis.
• Fever or other signs of infection in clients whose immune
systems are suppressed. Combinations of antibacterial
plus antiviral and/or antifungal drugs may be needed
PENICILLINS
Indications for Use
• Clinical indications for use of penicillins include
bacterial infections caused by susceptible
microorganisms. As a class, penicillins usually are more
effective in infections caused by gram-positive bacteria
than those caused by gram-negative bacteria. However,
their clinical uses vary significantly according to the
subgroup or individual drug and microbial patterns of
resistance. The drugs are often useful in skin/ soft
tissue, respiratory, gastrointestinal, and genitourinary
infections. However, the incidence of resistance among
streptococci, staphylococci, and other microorganisms
continues to grow.
Aminopenicillins
Piperacillin
Augmentin contains amoxicillin and
clavulanate. It is available in 250-,
500-, and 875-mg tablets, each of
which contains 125 mg of
clavulanate.
MACROLIDES
Cephalosporins
Indications for Use


Clinical indications for the use of cephalosporins include surgical
prophylaxis and treatment of infections of the respiratory tract, skin
and soft tissues, bones and joints, urinary tract, brain and spinal
cord, and bloodstream (septicemia). In most infections with
streptococci and staphylococci, penicillins are more effective and
less expensive. In infections caused by methicillin-resistant S.
aureus, cephalosporins are not clinically effective even if in vitro
testing indicates susceptibility. Infections caused by Neiserria
gonorrhoeae, once susceptible to penicillin, are now preferentially
treated with a third-generation cephalosporin such as ceftriaxone.
Cefepime is indicated for use in severe infections of the lower
respiratory and urinary tracts, skin and soft tissue, female
reproductive tract, and infebrile neutropenic clients. It may be used
as monotherapy for all infections caused by susceptible organisms
except P. aeruginosa; a combination of drugs should be used for
serious pseudomonal infections.
Aminoglycosides
Contraindications to Use

Aminoglycosides are contraindicated in infections
for which less toxic drugs are effective. The
drugs are nephrotoxic and ototoxic and must be
used very cautiously in the presence of renal
impairment. Dosages are adjusted according to
serum drug levels and creatinine clearance. The
drugs must also be used cautiously in clients
with myasthenia gravis and other neuromuscular
disorders because muscle weakness may be
increased.
Lincosamindes
Antibiotic
resistance
FLUOROQUINOLONES
ANTIVIRAL DRUGS
Drugs for HIV Infection and AIDS
(Antiretrovirals)
Antifungal Drug Mechanisms