Antibiotics II Flashcards by Kyra Porter

vancomycin - overview

*complex GLYCOPEPTIDE (large)
*interferes with cell wall synthesis (not in the same way as beta lactams): binds to D-Ala-D-Ala portion of cell wall precursors to inhibit cell wall peptidoglycan formation
*bactericidal (less rapidly than anti-staph penicillins)

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vancomycin - mechanism of action

*binds to d-alanine-d-alanine of peptide precursor
*inhibits peptidoglycan synthesis via steric hinderance

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vancomycin - mechanism of resistance

change from d-alanine-d-alanine to d-alanine-d-lactate

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vancomycin - spectrum

gram POSITIVE organisms (including MRSA & C diff)

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vancomycin - important pharmacokinetic property

*if given orally, it does NOT get into the bloodstream (good for C diff)
*if given IV, does not get into GI tract (bad for C diff)

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main drug for C diff ?

ORAL vancomycin

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dalbavancin

*complex lipoglycopeptide
*same mechanism of action as vancomycin
*LONG HALF LIFE (useful in infections of IV drug users)
*active against gram-positive bacteria

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antibiotic classes that inhibit the ribosome

macrolides (50S subunit - azithromycin, erythromycin, clarithromycin)
aminoglycosides (30S subunit - gentamicin, neomycin, amikacin, tobramycin, streptomycin)
clindamycin
tetracyclines (30S subunit - tetracycline, doxycycline, minocycline)

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macrolides - mechanism of action

*inhibits protein synthesis by blocking translocation; bind to 50S ribosomal subunit
*examples: azithromycin, erythromycin, clarithromycin

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macrolides - mechanism of resistance

*ribosomal methylation of 23S rRNA-binding site (prevents macrolide binding)
*examples of macrolides: azithromycin, erythromycin, clarithromycin

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examples of macrolides

erythromycin - use for pathogens without cell walls and gram positives; gives really bad diarrhea (we don’t use anymore)
azithromycin - better than erythro; common for respiratory tract infections
clarithromycin

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aminoglycosides - mechanism of action

*inhibit protein synthesis by binding to 30S subunit of ribosome
*examples: gentamicin, neomycin, amikacin, tobramycin, streptomycin

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pharmacodynamics for aminoglycosides

concentration-dependent killing: Cmax / MIC ( > 5)

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examples of aminoglycosides

-gentamicin
-tobramycin
-streptomycin
-amikacin

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aminoglycosides - spectrum of activity

*gram negative aerobes
*synergistic with beta lactams!

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aminoglycosides - mechanism of resistance

enzymatic inactivation of the drug itself (sulfation, acetylation, or phosphorylation)

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downsides of aminoglycosides

*low therapeutic index (may be toxic)
*need to monitor serum levels to limit toxicity (deafness, renal failure)

clindamycin - mechanism of action

inhibits protein synthesis by binding to 50S subunit of ribosome

clindamycin - mechanism of resistance

*ribosomal methylation

clindamycin - spectrum and uses

*gram positive cocci (staph and strep)
**used for Group A Strep (SHUTS DOWN TOXIN PRODUCTION for necrotizing fasciitis)
*above the diaphragm anaerobes

tetracyclines - mechanism of action

*inhibits protein synthesis by binding to 30S subunit of ribosome
*examples: tetracycline, doxycycline, minocyline

tetracyclines - mechanism of resistance

drug efflux

tetracyclines (especially doxycycline) - spectrum and uses

*gram positive, some gram negative
*MYCOPLASMA, CHLAMYDIA, RICKETTSIA, malaria
*go-to for tick-borne infections

TMP-SMX (trimethoprim-sulfamethoxazole / bactram) - mechanisms of action

*blocks 2 consecutive steps in FOLATE synthesis, thus blocking biosynthesis of nucleic acids
1. bacterial dihydrofolate reductase (PABA to folic acid)
2. dihydropteroate synthase (folic acid to folinic acid(

TMP/SXT - mechanism of resistance

increased production of dihydrofolate reductase (bacteria just makes a LOT more to overcome antibiotic)

TMP/SXT - spectrum

broad spectrum, including MRSA *used for pneumocystis jirovecii

metronidazole

***forms toxic free radical metabolites in the bacterial cell that damage DNA** *used for anaerobes BELOW the diaphragm

fluroquinolones - mechanism of action

***inhibits DNA gyrase / topoisomerase II** (stops DNA replication) *examples: **"-floxacins":** ciprofloxacin, ofloxacin, levoflaxacin, moxifloxacin

fluroquinolones - mechanism of resistance

1. mutation of DNA gyrase/topoisomerase 2. drug efflux

pharmacodynamics of fluroquinolones

AUC/MIC > 35

examples of fluroquinolones

-levofloxacin -moxifloxacin -ciprofloxacin

fluroquinolones - spectrum of activity

*ALL have good gram NEGATIVE activity (cipro best against pseudomonas) *ALL cover the "atypicals" (mycoplasma, chlamydia, legionella *covers TB

what drugs can be used for traveler's diarrhea

azithromycin or ciprofloxacin

rifampin - mechanism of action

**inhibits DNA-dependent RNA polymerase** *penetrates biofilms well

rifampin - mechanism of resistance

mutations in the DNA-dependent RNA polymerase

something to note about rifampin

body fluids turn ORANGE (tears, urine)

daptomycin - mechanism of action

***a LIPOPEPTIDE that disrupts cell membranes of gram positive cocci by creating transmembrane channels** *calcium-dependent increase in membrane permeability to potassium

daptomycin - spectrum

all gram positives, including MRSA

linezolid - mechanism of action

*inhibits protein synthesis by **binding to the 23S rRNA of the 50S ribosomal subunit** and preventing formation of the initiation complex *can be used for MRSA

polymxin B - mechanism of action

**intercalates with LPS in gram negative membrane** *we don't use it anymore (toxic)

fidaxomicin

*nonabsorbable oral drug *useful for C diff *VERY expensive (we should use vancomycin) *example of a macrolide