Antibiotics IV Flashcards
What are the 3 drug classes that inhibit bacterial nucleic acid synthesis?
- Fluoroquinolones
- Rifampin
- Metronizadole
What is the first generation FQ? Mechanism?
Ciprofloxacin; Inhibit DNA gyrase
What is the 2nd generation FQ? Mechanism?
Levofloxacin; Inhibit gyrase and bacterial topoisomerase IV
Why are FQs typically well-tolerated?
Humans don’t have DNA gyrase and therefore the drugs are well-tolerated
What additional spectrum is added in 2nd generation FQs?
Streptococcus pneumoniae
Adverse SEs of FQs
- Allergy
- Second Generation FQs may cause polymorphic ventricular tachycardia (Torsades de Pointes)
MOA of rifampin?
Inhibition of DNA-dependent RNA polymerase to stop the replication of RNA from the daughter DNA strand
Adverse SEs of Rifampin?
- Allergy
- Possible centrolobular hepatitis when used with isonazid
AB spectrum of rifampin?
- Mycobacterium tuberculosis
- Staphylococcus aureus
What is the MOA of Metronidazole?
Prodrug that is activated in an anaerobic environment to a drug that is toxic to nucleic acids
Adverse SE of Metronidazole?
- Allergy
- Inhibits aldehyde dehydrogenase to cause profound vasodilation and tachyarrhythmias due to the accumulation of acetyl aldehyde when metronidazole is taken with ethanol
What is the AB spectrum of metronidazole?
- Anaerobic bacteria such as Clostridium difficile
- Selected Protozoa (Entamoeba histolytica, Giardia lamblia)
What are the 30S ribosome inhibitors?
- Aminoglycosides (gentimicin, tobramycin)
- Tetracyclines (Doxycycline)
What are the 50S Ribosome inhibitors?
- Macrolides (azithromycin)
- Linezolid
What is the mechanism of gentamicin?
The aminoglycoside binds to the 30S ribosome which causes the transfer of the incorrect amino acyl transfer RNA and hence the wrong amino acid
To what bugs are aminoglycosides restricted? Why?
Aerobic or facultative aerobic Gram (-) rods; To enter cells, AGs must be uptaken by an oxygen dependent method
What is important about the administration of AGs?
They have rapid lethality and superior prolonged AB effect on Gram (-) rods
What is the spectrum of AGs?
Gram negative rods (Enterobacteriacaie) because of ESBL and Carbapenemase-producing strains of Enterobacter cloacae; Furthermore, FQs, 3rd gen cephs. and ES penicillins have promoted resistance
What is an important consideration in AG administration in regards to SEs?
While AGs are nephrotoxic, they are only nephrotoxic when they accumulate in the kidney. Therefore, nephrotoxicity is not observed if use is < 48hrs
When is AG (gentamicin) use most efficacious?
W/i first 12-24 hrs after exposure
What is the MOA for Doxycycline?
Tetracycline that blocks the access of the tRNA anticodon to its codon
What is the AB spectrum of tetracyclines?
Doxycycline is effective for intracellular pathogens (mycoplasma, chlamydia, legionella, rickettsia); Gram (+) organisms (S. pneumoniae, MRSA) in face of resistance to lactams
Adverse SEs of doxycycline?
- Allergy
- Photosensitivity RXN
- Not orally bioavailable when administered w/ di/tri-valent cations due to chelation
MOA for azithromycin?
Macrolide that prevents the release and removal of the “naked” transfer RNA from the “A” site into the cytoplasm (inhibits transolcation by inhibiting translocase enzyme)
Spectrum of Azithromycin?
Effective for intracellular pathogens (mycoplasma, chlamydia, legionella), H. influenzae, Gram (+) organisms [pneumococci, MRSA] that have lactam resistance
Adverse SEs of Macrolides?
- allergy
- GI distress with oral administration
- Potential of Torsades de pointes
What is the most likely method of AB resistance for azithromycin or doxycycline?
Methylation of the target site or efflux pump
MOA of Linezolid?
Inhibit transfer of the peptide chain from the “A” site to the P” site via the inhibition of the peptidyl transferase
Spectrum of Linezolid?
Gram (+) organisms; It was primarily developed for infections of MRSA and VRSA
Adverse Rxns to Linezolid?
- Allergy
- Agranulocytosis with prolonged use
MOA of clindamycin?
Inhibit incorporation of new AA into growing peptide chain
Clindamycin spectrum?
All anerobes except C. difficile, pneumococci and MRSA in face of lactam resistance
Adverse effects of Clindamycin?
- allergy
- AB most closely associated with C. difficile colitis
