macrolides, clindamycin, tetracyclines Flashcards
Which of the following is/are true?
A. tetracyclines bind reversibly to 50s ribosomal subunit and inhibits RNA dependent protein synthesis
B. the most frequent type of macrolide resistance is ribosomal methylation
C. S. aureus obtains macrolide resistance via via alteration of the 50S ribosomal subunit
D. enterobacterales resist macrolides by inactivating enzymes
E. A and B
F. A and C
G. B and C
H. C and D
correct: H
A. FALSE - macrolides
B. FALSE - active efflux
C. TRUE - also S. pyogenes, E. coli
D. TRUE
Which of the following is not a mechanism of macrolide resistance? A. cell wall permeability B. 50S ribosomal methylation C. alteration of 50S ribosomal subunit D. active efflux E. enzyme inactivation
psyche - they are all mechanisms of macrolide resistance
which organism(s) employ each of the mechanisms of macrolide resistance below?
- active efflux
- alteration of the 50S ribosomal subunit
- enzyme inactivation
- active efflux - staphylococci, S. pyogenes, S. pneumoniae
- alteration of the 50S ribosomal subunit - S. aureus, S. pyogenes, E. coli
- enzyme inactivation - enterobacterales
Which of the following is false?
A. cross resistance between macrolides is common
B. clindamycin may compete with a macrolide for the same binding site
C. azithromycin becomes concentrated inside macrophages and cytotoxic T cells
D. azithromycin is predominantly metabolized by the liver
E. C and D are both false
correct: E
A. TRUE
B. TRUE - also chloraphenicol
C. FALSE - macrophages and polymorphonuclear neutrophils
D. FALSE - clarithromycin is; azithromycin is minimally metabolized by liver, excreted in bile and feces
Which of the following is/are true about clarithromycin? A. is acid stable B. should be taken with food C. has wide tissue distribution D. metabolized mostly by liver E. none of the above F. A and B G. A, B, C H. A, C, D
correct: H
A. true
B. FALSE - w/ or w/o food
C. true
D. true
Which of the following about macrolide resistant mechanisms is false?
A. staphylococci, S. pyogenes and S. pneumoniae resist macrolides via active efflux
B. S. aureus, S. pyogenes and E. coli resist macrolides via altering their 50S ribosomal subunit
C. enterobacterales inactivate enzymes
D. all of the above
E. none of the above
correct: D
A. true
B. true
C. true
Which of the following medications must be renally dosed if CrCl < 30 mL/min. A. clarithromycin B. azithromycin C. clindamycin D. all of the above E. B and C only
correct: A
A. yes
B. no - azithromycin eliminated mostly via bile and feces
C. no - note clindamycin is not a macrolide; it’s a lincosamide
Which AE(s) is/are not associated with clarithromycin? A. QT interval elongation B. thrombocytopenia C. tooth discolouration D. fetal abnormalities in animals E. all of the above F. none of the above
correct: B - thrombocytopenia is an AE of clindamycin
Which of the following is true?
A. increasing order of QT interval risk: erythromycin > clarithromycin > azithromycin
B. azithromycin is contraindicated in pneumococcal pneumoniae infections
C. the 14-hydroxy metabolite is active and synergetic with erythromycin
D. clarithromycin is contraindicated in pregnancy
E. out of all the macrolides, azithromycin interacts with the most drugs
F. A and D
G. B, C, E
correct: F
A. true
B. false - use with caution - risk of bacteremia b/c of low blood levels
C. false - clarithromycin
D. true - clarithromycin is teratogenic, azithromycin is safe
E. false - clarithromycin; azithromycin has the least drug interactions
Which of the following is false?
A. erythromycin is concentrated inside polymorphnuclear neutrophils and macrophages
B. erythromycin metabolites inhibit CYP3A4
C. clindamycin causes hepatotoxicity
D. a pt with resistance to minocycline will likely have to be txed with an abx of a diff class
E. all are true
correct: A
A. false - azithromycin
B. true - erythromycin and clarithromycin form inactive complexes with CYP3A4, resulting in the enzyme’s inhibition
C. true - reversible increase in transaminases, rarely hepatocellular damage
D. true - tetracycline cross-resistance exists, and it usually involves all agents
Which of the following is true?
A. dose reduction may be necessary for drugs metabolized by CYP3A4 if azithromycin is administered concurrently
B. clindamycin is indicated for the tx of necrotizing fascitis
C. PO clindamycin palmitate is poorly absorbed
D. clindamycin phosphate is administered via IV
E. all of the above
F. A and C
G. A and D
H. B and D
correct:
A. false - erythromycin and clarithromcyin bind CYP3A4 to create inactive complexes - CYP3A4 becomes inactivated by this binding - this decreases the metabolization of drugs that are supposed to be metabolized by this enzyme, thus increasing their serum levels
B. true - clindamycin decreases toxin production of S. aureus and S. pyogenes - good for necrotizing fascitis
C. false - 90% absorbed; slight delay with food
D. true
Which of the following is false about clindamycin?
A. reduces toxin production of S. aureus and S. pyogenes
B. competes with azithromycin for the same binding sites
C. penetrates most tissues except CSF
D. metabolized in liver
E. A and B
F. B and C
G. all of the above
H. none of the above
correct: H - none of the above are false
A. true
B. true - macrolides compete with chloraphenicol and clindamycin for the same binding sites
C. true
D. true
Which of the following is true about tetracyclines?
A. minocycline and tetracycline are long-acting agents
B. enters cells passively to bind 30S ribosomal subunit and block binding of aminoacyl tRNA
C. mechanisms of resistance mostly occur via chemical alteration
correct:
A. false - minocycline and doxycycline
B. true
C. false - most via decreased influx or active export; rarely inactivated or chemically altered
Clindamycin resistance occurs via…
A. alteration of 50S ribosomal receptor site and active efflux
B. alteration of 50S ribosomal receptor site and enzyme inactivation
C. intrinsic resistance w/ enterobacterales and pseudomonas and cell permeability
D. alteration of 23S ribosomal RNA of 50S ribosomal subunit and decreased active efflux
E. none of the above
B
alteration of 50S ribosomal receptor site
alteration of 23S ribosomal RNA of 50S ribosomal subunit
enzyme inactivation
intrinsic resistance w/ enterobacterales and pseudomonas
tetracycline absorption is decreased if taken with food except for:
A. doxycycline and tetracycline
B. doxycycline, minocycline, chlortetracycline
C. minocycline and oxytetracycline
D. tetracycline, minocycline and chlortetracycline
E. doxycycline and minocycline
F. none of the above
correct: E
decreased tetracycline absorption also w/ Al, Ca, Mg, Fe, Zn, Na HCO3
