B4 Q/A

Question 1

The  chemotherapy  undertaken  by  this  patient  caused  acute 
hemorrhagic  cystitis.  Which  drug  was  most  likely  to  be 
responsible  for  this  toxicity? 
(A)  Cyclophosphamide 
(B)  Doxorubicin 
(C)  Fluorouracil 
(0) Methotrexate 
(E)  Tamoxifen

Answer 1

Cyclophosphamide

Acrolein, a toxic metabolite of cyclophosphamide that is con-
centrated in the urine, is associated with hemorrhagic cystitis.
Mesna, a sulfur-containing substance that also concentrates in
urine, can be administered in an attempt to prevent this com-
plication.

Question 2

Which one of he following statements about the
of beta-Iactam antibiotics is not accurate?
(A) First-generation cephalosporins do not cross the blood-brain
barrier even when the meninges are inf1arned
(B) Labi li ty of penicillins in gastric acid can limit their oral
absorption
(C) Nafcillin and ceftriaxone are eliminated mainly via biliary
secretlon
(0) Procaine penicillin G is used via intramuscular injection
(E) The renal tubular reabsorption of amoxicillin is inhibited
by probenecid

Answer 2

The renal tubular reabsorption of amoxicillin is inhibited
by probenecid

First- and second-generation cephalosporins are not effective
in bacterial meningitis, si nce they do not readily enter the
cerebrospin al f1uid. Proca in e penicill in G is given by intra-
muscular injection but used now owing to resistance
on the part of gonococci and pneumococci. T he elimination
half- li ves of many beta-Iactam amibiotics are prolonged by
probenecid, wh ich inhibits their proximal tubular secretion

Question 3

The primary mechanism of antibacterial action of the penicillins
involves inhibition of
(A) Beta lactamaces
(B) Cell membrane synthesis
(C) N-acetylmuramic acid synthesis
(D) Reactions involving transpeptidation
(E) Transglycosylation

Answer 3

Reactions involving transpeptidation

Question 4

3-4. A 21-yr-old man was seen in a clinic with a complaint of
dysuria and urethral discharge of yellow pus. He had a painless clean-based ulcer on the penis and nontender enlargement of the regionally mph nodes. Gram stain of the urethral exudate showed gram-negative diplococci within polymorphonucleocytes. The patient informed the clinic staff that he was unemployed and had not eaten a meal for 2 days.

3. T he mos t appropriate treatment of gonorrhea in this patient

(A) Amoxicillin orally for 7 d
(B) Ceft riaxone intramuscularly as a single dose
(C) Procaine penicillin G intramuscularly as a single dose
plus oral probenecid
(D) Tetracycl ine orally for 7 d
(E) Vancomycin intramuscularly as a single dose

Answer 4

Ceftriaxone intramuscularly as a single dose

Currently, the treatments of choice for gonorrhea include a
single dose of ceftriaxone (intramuscularly). Because of the
high incidence of beta- Iactamase-producing gonococci , the
use of penicillin G or amoxicillin is no longer appropriate for
gonorrhea. Similarly, many st rains of go nococci are resistant
to tetracyclines. Al ternative drugs (not listed) for gonorrhea
include cefìxime, azithromyci n (see Chapter 44) or spect ino-
mycin (see Chapter 45).

Question 5

Immunofluorescent microscopic examination of fluid expressed
from the penile chancre of this patient revealed treponemes.
Because he appears to be infected with Treponema pallidum,
the best course of action would be to
(A) Give a single oral dose of fos fomycin
(B) Give no other antibiotics because drug treatment of
gonorrhea provides coverage for incubating syphilis
(C) Inject intramuscular benzathine penicillin G
(D) Treat with oral tetracycl ine for 7 d
(E) Treat with vancomycin

Answer 5

Inject intramuscular benzathine penicillin G

This patient with gonorrhea also has primary syphilis. The
penile chancre, the enlarged nontender Iymph the
microscopic identifìcation of reponemes in f1 uid expressed from
the lesion are essentials of diagnosis. Al though a single dose of
may syphilis, it cannot be relied on
for primary syphilis. The most appropriate course of
act ion in this patient is to administer a single intramuscular
injection of 2.4 million units of benzathine penicillin G. For
penicillin-allergic oral doxycycline or tetracycline for
15 d is effective in most cases (see Chapter 44). However, lack
of compliance may be a problem with oral therapy. Fosfomycin
and vancomycin have no signifìcant activiry spirochetes.

Question 6

Which of the following best describes the mechanism of
anticancer action of cellular metabolites of fluorouracil?
(A) Cross-linking of double-stranded DNA
(B) Inhibition of DNA-dependent RNA synthesis
(c) Interference with the activity of topoisomerases 1
(0) Irreversible inhibition of thymidylate synthase
(E) Selective inhibition of DNA polymerases

Answer 6

Irreversible inhibition of thymidylate synthase

Fluorouracil (5-FU) undergoes metabolism to form
2’-deoxyuridine 5’-phosphate (5-dUMP). This metabolite
forms a covalendy bound ternary complex with thymidylate
synthase and its coenzyme N-methylenetetrahydrofolate. The
synthesis of hymine nucleotides is blocked, DNA synthesis is
inhibited, and a “thymineless death” of cells resu!ts