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188 SEcTioN ii Microbiology ` microbiology—aNtimicrobials Microbiology ` microbiology—aNtimicrobials

Penicillinase-sensitive
penicillins Amoxicillin, ampicillin; aminopenicillins.

mecHaNism Same as penicillin. Wider spectrum; AMinoPenicillins are AMPed-up penicillin.
penicillinase sensitive. Also combine with AmOxicillin has greater Oral bioavailability
clavulanic acid to protect against destruction than ampicillin.
by β-lactamase.

cliNical Use Extended-spectrum penicillin—H influenzae, Coverage: ampicillin/amoxicillin HHELPSS
H pylori, E coli, Listeria monocytogenes, kill enterococci.
Proteus mirabilis, Salmonella, Shigella,
enterococci.

aDVerse eFFects Hypersensitivity reactions, rash,
pseudomembranous colitis.
mecHaNism oF resistaNce Penicillinase (a type of β-lactamase) cleaves
β-lactam ring.

Penicillinase-resistant
penicillins Dicloxacillin, nafcillin, oxacillin.

mecHaNism Same as penicillin. Narrow spectrum;
penicillinase resistant because bulky R group
blocks access of β-lactamase to β-lactam ring.
cliNical Use S aureus (except MRSA). “Use naf (nafcillin) for staph.”
aDVerse eFFects Hypersensitivity reactions, interstitial nephritis.
mecHaNism oF resistaNce MRSA has altered penicillin-binding protein
target site.

Antipseudomonal
penicillins Piperacillin, ticarcillin.
mecHaNism Same as penicillin. Extended spectrum. Penicillinase sensitive; use with β-lactamase inhibitors.
cliNical Use Pseudomonas spp. and gram ⊝ rods.
aDVerse eFFects Hypersensitivity reactions.

FAS1_2019_03-Microbiology.indd 188 11/14/19 12:22 PM