Inhibitors of Bacterial Nucleic Acid Synthesis

Inhibitors of Bacterial Nucleic Acid Synthesis
Inhibitors of Bacterial Nucleic Acid Synthesis
Questions 1−3
1. B
2. E
3. A
Learning objective: Describe the antibacterial spectrum of
uoroquinolones.
4. C Cipro oxacin is a uoroquinolone antibiotic. These drugs
have a broad antibacterial spectrum that includes som e gram –
positive bacteria, m ost gram -negative bacteria, and som e
m ycobacteria, mycoplasm as, chlamydiae, and rickettsiae.
A, B Piperacillin and ceftazidim e are e ective against Pseudom onas aeruginosa but not against m ycobacteria, m ycoplasm as, chlamydiae, and rickettsiae.
D Erythromycin is e ective against mycobacteria, mycoplasm as, chlamydiae, and rickettsiae but not against P. aeruginosa and mycobacteria.
E Vancom ycin is e ective only against gram -positive
bacteria.
Learning objective: Explain the mechanism of resistance to
sulfonamides.
5. C Many bacteria originally sensitive to sulfonam ides are now
resistant. Resistance to trim ethoprim -sulfam ethoxazole is less
frequent than resistance to either of the agents alone, but it
still occurs in several cases. When resistance develops, it is
usually persistent and irreversible. Mechanism s of resistance
to sulfonam ides are
• Decreased a nity for sulfonam ides by dihydropteroate
synthetase
• Decreased bacterial perm eability to the drug
• Increased production of para-am inobenzoic acid (PABA).
For exam ple, som e resistant staphylococci m ay synthesize
70 tim es as m uch PABA as do the susceptible parental
strains.
A, E These m echanism s would increase, not decrease, the
bacterial sensitivity to sulfonam ides.
B Sulfonam ides do not act by binding to bacterial ribosom es.
D Sulfonam ides do not act by binding to dihydrofolate
reductase.
Learning objective: Identify the drug that can cause dermatitis in
a previously sensitized person.
Inhibitors of Bacterial Nucleic Acid Synthesis
6. C The patient’s history and sym ptom s suggest that he had
an allergic reaction to trim ethoprim -sulfam etoxazole. Rash
is a com m on adverse e ect associated w ith sulfonam ide use
and is m ost frequently due to hypersensitivit y. Moreover,
trim ethoprim -sulfam ethoxazole has been reported to cause
up to three tim es as m any derm atologic reactions as do sulfonam ides alone.
A, B, D, E These drugs are not currently used to treat acute
pharyngitis, and they are not given orally.
Learning objective: Describe the adverse e ects of uoroquinolones.
7. E Fluoroquinolones have been associated w ith an increased
risk of tendon rupture that can occur even after short-term
use of these drugs. This adverse e ect has been o cially reported in literally hundreds of patients. The mechanism of
this action seem s related to a direct cytotoxic e ect of the
drug on the ligament tissue. In fact, in vitro, exposure of tendon tissue to cipro oxacin resulted in a decrease in fibroblast
proliferation, a decrease in collagen synthesis, and a sign –
cant increase in m matrix-degrading proteolytic activity.
A−D These drugs do not cause tendon rupture.
Learning objective: Describe the main drug interactions with
fluoroquinolones.
8. A Products containing divalent and trivalent cations (Mg2 ,
Ca2 , Zn2 , Al3 , Fe2 ), such as antacids, milk products, and
Fe2 -containing medications, invariably cause a sign cant
decrease in intestinal absorption of fluoroquinolones (up to
70%) because fluoroquinolones can chelate the cations, form –
ing insoluble compounds. This may result in therapeutic failures. It is therefore imperative that clinicians question patients
regarding other medications, both prescription and nonprescription, that they may be taking and instruct them to avoid
certain products, as in this case.
B−E See the correct answer explanation.
Learning objective: Outline the therapeutic uses of cipro oxacin.
Inhibitors of Bacterial Nucleic Acid Synthesis
9. B The patient’s history and symptoms indicate that he was
m ost likely suffering from traveler’s diarrhea, a disease de-
ned as three or more loose stools per day plus at least one
enteric sym pm. The disease is due to Enterobacteriaceae,
with Escherichia coli being the causative agent in more than
50% of cases. Many antimicrobial agents have been shown
to shorten the duration and severity of diarrhea, but because
of the increasing resistance of Enterobacteriaceae, currently
fluoroquinolones, and to a lesser extent trim ethogram -sulfa eth oxazole, are recommended for the em price treatment of
traveler’s diarrhea.
A, C−F These drugs are not active against most Enterobacteriaceae.
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