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192 SEcTioN ii Microbiology ` microbiology—aNtimicrobials Microbiology ` microbiology—aNtimicrobials

Tetracyclines Tetracycline, doxycycline, minocycline.
mecHaNism Bacteriostatic; bind to 30S and prevent attachment of aminoacyl-tRNA. Limited CNS penetration.
Doxycycline is fecally eliminated and can be used in patients with renal failure. Do not take
2+
tetracyclines with milk (Ca ), antacids (eg, Ca or Mg ), or iron-containing preparations
2+
2+
because divalent cations inhibit drugs’ absorption in the gut.
cliNical Use Borrelia burgdorferi, M pneumoniae. Drugs’ ability to accumulate intracellularly makes them very
effective against Rickettsia and Chlamydia. Also used to treat acne. Doxycycline effective against
community-acquired MRSA.
aDVerse eFFects GI distress, discoloration of teeth and inhibition of bone growth in children, photosensitivity.
Contraindicated in pregnancy.
mecHaNism oF resistaNce  uptake or  efflux out of bacterial cells by plasmid-encoded transport pumps.

Tigecycline
mecHaNism Tetracycline derivative. Binds to 30S, inhibiting protein synthesis. Generally bacteriostatic.
cliNical Use Broad-spectrum anaerobic, gram ⊝, and gram ⊕ coverage. Multidrug-resistant organisms (MRSA,
VRE) or infections requiring deep tissue penetration.
aDVerse eFFects GI symptoms: nausea, vomiting.

Chloramphenicol

mecHaNism Blocks peptidyltransferase at 50S ribosomal subunit. Bacteriostatic.
cliNical Use Meningitis (Haemophilus influenzae, Neisseria meningitidis, Streptococcus pneumoniae) and
rickettsial diseases (eg, Rocky Mountain spotted fever [Rickettsia rickettsii]).
Limited use due to toxicity but often still used in developing countries because of low cost.
aDVerse eFFects Anemia (dose dependent), aplastic anemia (dose independent), gray baby syndrome (in premature
infants because they lack liver UDP-glucuronosyltransferase).
mecHaNism oF resistaNce Plasmid-encoded acetyltransferase inactivates the drug.

Clindamycin

mecHaNism Blocks peptide transfer (translocation) at 50S
ribosomal subunit. Bacteriostatic.
cliNical Use Anaerobic infections (eg, Bacteroides spp., Treats anaerobic infections above the diaphragm
Clostridium perfringens) in aspiration vs metronidazole (anaerobic infections below
pneumonia, lung abscesses, and oral diaphragm).
infections. Also effective against invasive
group A streptococcal infection.
aDVerse eFFects Pseudomembranous colitis (C difficile
overgrowth), fever, diarrhea.

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