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Microbiology ` microbiology—aNtimicrobials Microbiology ` microbiology—aNtimicrobials SEcTioN ii 193
Linezolid
mecHaNism Inhibits protein synthesis by binding to 50S subunit and preventing formation of the initiation
complex.
cliNical Use Gram ⊕ species including MRSA and VRE.
aDVerse eFFects Bone marrow suppression (especially thrombocytopenia), peripheral neuropathy, serotonin
syndrome (due to partial MAO inhibition).
mecHaNism oF resistaNce Point mutation of ribosomal RNA.
Macrolides Azithromycin, clarithromycin, erythromycin.
mecHaNism Inhibit protein synthesis by blocking translocation (“macroslides”); bind to the 23S rRNA of the
50S ribosomal subunit. Bacteriostatic.
cliNical Use Atypical pneumonias (Mycoplasma, Chlamydia, Legionella), STIs (Chlamydia), gram ⊕ cocci
(streptococcal infections in patients allergic to penicillin), and B pertussis.
aDVerse eFFects MACRO: Gastrointestinal Motility issues, Arrhythmia caused by prolonged QT interval, acute
Cholestatic hepatitis, Rash, eOsinophilia. Increases serum concentration of theophylline, oral
anticoagulants. Clarithromycin and erythromycin inhibit cytochrome P-450.
mecHaNism oF resistaNce Methylation of 23S rRNA-binding site prevents binding of drug.
Polymyxins Colistin (polymyxin E), polymyxin B.
mecHaNism Cation polypeptides that bind to phospholipids on cell membrane of gram ⊝ bacteria. Disrupt cell
membrane integrity leakage of cellular components cell death.
cliNical Use Salvage therapy for multidrug-resistant gram ⊝ bacteria (eg, P aeruginosa, E coli, K pneumoniae).
Polymyxin B is a component of a triple antibiotic ointment used for superficial skin infections.
aDVerse eFFects Nephrotoxicity, neurotoxicity (eg, slurred speech, weakness, paresthesias), respiratory failure.
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