Flashcards in Review - Antibacterial Agents Deck (39):
What is a bacteriostatic antibiotic?
An antibiotic that causes REVERSIBLE inhibition of growth.
What is a bactericidal antibiotic?
An antibiotic that causes IRREVERSIBLE inhibition of growth.
Why should bacteriostatic and bacteriocidal antibiotics not be given together?
Bacteriostatic drugs will antagonize the effects of bacteriocidal drugs which rely on the active replication and utilization of environmental resources by bacteria.
Vancomycin-resistant bacteria change their D-ala-D-ala terminus of the peptide side chain to what?
How can vancomycin-induced "red-man" syndrome be prevented?
By slowing the infusion rate. Infusion over 1-2h is normally sufficient.
Also antihistamines can be administered.
Which antibiotic inhibits the phosphorylation/dephosphorylation cycling of the lipid carrier required in the transfer of peptidoglycan to the cell wall?
Bacitracin - topically due to severe nephrotoxicity.
Do humans possess dihydropteroate synthase?
Therefore sulfonamides are SELECTIVELY toxic to bacteria and other microorganisms.
Are sulfonamides bactericidal or bacteriostatic?
Why are sulfonamides contraindicated in neonates?
They displace bilirubin from albumin thereby causing kernicterus in neonates.
Give examples of how bacteria become resistant to sulfonamides.
1. Incr. concentration of PABA
2. Decr. binding affinity of target enzymes
3. Uptake and use of exogenous sources of folic acid
Give examples of how bacteria may become resistant to fluoroquinolones?
1. Reduced drug penetration (drug efflux pumps)
2. Mutations in DNA gyrases result in decreased binding affinity of bacterial target enzymes for fluoroquinolones.
Give examples of how bacteria may become resistant to beta lactam antibiotics.
1. Production of beta lactamases (MC mechanism).
2. Alteration of penicillin binding proteins.
3. Inhibition of drugs to reach PBPs.
4. Downregulation of porin structure (only in gram(-)).
5. Development of efflux pumps (only in gram(-)).
Can a monobactam be used in a penicillin-allergic patient?
Yes. This makes monobactams a good choice for patients with a penicillin allergy and a serious gram(-) infection.
Penicillins are synergistic with what other antibiotic class in the Tx of enterococcal and pseudomonas infections?
Penicillins inhibit cell wall synthesis so aminoglycosides are able to enter the cells.
Name 3 beta lactamase inhibitors that can be used in combination with penicillins.
What is the mechanism of methicillin resistance by S.aureus?
Production of an alternative PBP 2a.
How do the antibiotic spectrum of cephalosporins vary by generation?
2nd gen --> Incr. gram(-) coverage.
3rd gen --> More incr. gram(-) coverage + cross BBB.
4th gen --> Incr. beta lactamase resistance.
What is the difference in microbial coverage between imipenem and ertapenem?
Ertapenem does not cover Acinetobacter species and pseudomonal species.
What is streptomycin commonly used to treat?
Why might the efficacy of an aminoglycoside be increased when given as a single large dose as opposed to multiple smaller doses (2 reasons)?
1. Concentration-dependent killing
2. Post-antibiotic effect
Although synergistic in their effects, why can penicillins and aminoglycosides not be given in the same vial?
The penicillins would directly inactivate the aminoglycosides.
In regards to aminoglycoside ototoxicity, are high frequency or low frequency sounds affected first?
Give examples of how bacteria may become resistant to aminoglycosides.
1. Inactivation of drug via conjugation reactions (acetylation, adenylation, phosphorylation).
2. Inactivation driven by plasmid-encoded enzymes.
Which aminoglycoside antibiotic is the most toxic?
Neomycin (used primarily for topical application).
Why is a single dose of azithromycin as effective as a 7-day course of doxycycline for chlamydial infections?
Azithromycin has a very long half-life of 68h.
Which of the macrolides is relative free of drug-drug interactions?
Which macrolide can cause hepatotoxicity and blurred vision?
Give examples of how bacteria may become resistant to macrolides.
1. Alteration of binding sites on the 50S ribosomal subunit.
2. Reduced permeability of cell membrane
3. Active efflux
4. Production of esterases by bacteria that hydrolyze the drug
What organisms does clarithromycin cover that erythromycin does not?
Mycobacterium avium complex, M.leprae, Toxoplasma gondii
Which macrolide is safe in pregnancy?
What is demeclocycline used for?
SIADH via inhibition of ADH receptors in the renal collecting ducts.
Oral absorption of tetracyclines may be decreased by which multivalent cations?
Give examples of how bacteria become resistant to tetracyclines.
1. Efflux pumps or impaired influx.
2. Bacterial production of proteins that decrease binding of tetracyclines to ribosome.
3. Enzymatic inactivation.
Is tigecycline effective against MRSA?
Is tigecycline a substrate for the efflux pump mechanism of resistance to tetracyclines?
Give an example of an oxazolidinone antibiotic.
Which antibiotic, that works by inhibiting protein synthesis, can also be used in patients to increase GI motility?
Erythromycin (activates motilin receptors).
Which one of the 4 main TB drugs (rifampin, isoniazid, pyrazinamide, ethambutol) is bacteriostatic?