Protein synthesis inhibitors

Study Questions

Choose the ONE best answer.


QUESTIONS


1. A 2-year-old child is brought to the hospital after ingesting pills that a parent had used for bacterial  dysentery when traveling outside the United States. The child has been vomiting for more than 24 h and has had diarrhea with green stools. He is now lethargic with an ashen color. Other signs and symptoms include hypothermia, hypotension, and abdominal distention. The drug most likely to be the cause of this problem is


(A) Ampicillin

(B) Chloramphenicol

(C) Clindamycin

(D) Doxycycline

(E) Erythromycin


2. The mechanism of antibacterial action of doxycycline involves


(A) Antagonism of bacterial translocase activity

(B) Binding to a component of the 50S ribosomal subunit

(C) Inhibition of DNA-dependent RNA polymerase

(D) Interference with binding of aminoacyl-tRNA to bacterial ribosomes

(E) Selective inhibition of ribosomal peptidyl transferases


3. Clarithromycin and erythromycin have very similar spectra of antimicrobial activity. The major advantage of clarithromycin is that it


(A) Does not inhibit hepatic drug-metabolizing enzymes

(B) Eradicates mycoplasmal infections in a single dose

(C) Has greater activity against M avium-intracellulare complex

(D) Is active against methicillin-resistant strains of staphylococci

(E) Is active against strains of streptococci that are resistant to erythromycin


4. The primary mechanism of resistance of gram-positive organisms to erythromycin is


(A) Decreased activity of uptake mechanisms

(B) Decreased drug permeability of the cytoplasmic membrane

(C) Formation of drug-inactivating acetyltransferases

(D) Formation of esterases that hydrolyze the lactone ring

(E) Methylation of binding sites on the 50S ribosomal subunit


5. A 26-year-old woman was treated for a suspected chlamydial infection at a neighborhood clinic. She was given a prescription for oral doxycycline to be taken for 10 d. Three weeks later, she returned to the clinic with a mucopurulent cervicitis. On questioning she admitted not having the prescription filled. The best course of action at this point would be to 


(A) Delay drug treatment until the infecting organism is identified

(B) Rewrite the original prescription for oral doxycycline

(C) Treat her in the clinic with a single oral dose of cefixime

(D) Treat her in the clinic with a single oral dose of azithromycin

(E) Write a prescription for oral erythromycin for 10 d


6. A 55-year-old patient with a prosthetic heart valve is to undergo a periodontal procedure involving scaling and root planing. Several years ago, the patient had a severe allergic reaction to procaine penicillin G. Regarding prophylaxis against bacterial endocarditis, which one of the following drugs taken orally is most appropriate?


(A) Amoxicillin 10 min before the procedure

(B) Clindamycin 1 h before the procedure

(C) Erythromycin 1 h before the procedure and 4 h after the procedure

(D) Vancomycin 15 min before the procedure

(E) No prophylaxis is needed because this patient is in the negligible risk category


7. A 24-year-old woman comes to a clinic with complaints of dry cough, headache, fever, and malaise, which have lasted 3 or 4 d. She appears to have some respiratory difficulty, and chest examination reveals rales but no other obvious signs of pulmonary involvement. However, extensive patchy infiltrates are seen on chest x-ray film. Gram stain of expectorated sputum fails to reveal any bacterial pathogens. The patient mentions that a colleague at work has similar symptoms to those she is experiencing. The patient has no history of serious medical problems. She takes loratadine for allergies and supplementary iron tablets, and she drinks at least 6 cups of caffeinated coffee per day. The physician makes an initial diagnosis of community-acquired pneumonia. Regarding the treatment of this patient, which of the following drugs is most suitable?


(A) Amoxicillin

(B) Clindamycin

(C) Doxycycline

(D) Linezolid

(E) Vancomycin



8. If the patient is  treated with the macrolide erythromycin, he should:


(A) Avoid exposure to sunlight

(B) Avoid taking supplementary iron tablets

(C) Decrease her intake of caffeinated beverages

(D) Discontinue loratadine temporarily

(E) Have her plasma urea nitrogen or creatinine checked before treatment







9. A 5 day course of treatment for community-acquired pneumonia would be effective with little risk of drug interactions if the drug prescribed is


(A) Ampicillin

(B) Azithromycin

(C) Clindamycin

(D) Erythromycin

(E) Vancomycin



10. Concerning quinupristin-dalfopristin, which statement is accurate?


(A) Active in treatment of infections caused by E. faecalis

(B) Bacteriostatic

(C) Hepatotoxicity has led to FDA drug alerts

(D) Induce formation of hepatic drug-metabolizing enzymes

(E) Used in management of multidrug-resistant streptococci, MRSA, and vancomycin-resistant enterococci.



11. Regarding the mechanism of action of aminoglycosides, the drugs


(A) Are bacteriostatic

(B) Bind to the 50S ribosomal subunit

(C) Cause misreading of the code on the mRNA template

(D) Inhibit peptidyl transferase

(E) Stabilize polysomes


12. A 50-kg patient with creatinine clearance of 80 mL/min has a gram-negative infection. Amikacin is administered intramuscularly at dose of 5 mg/kg every 8 h, and the patient begins to respond. After 2 d, creatinine clearance declines to 40 mL/min. Assuming that no information is available about amikacin plasma levels, what would be the most reasonable approach to management of the patient at this point?


(A) Administer 5 mg/kg every 12 h

(B) Decrease the dosage to a daily total of 200 mg

(C) Decrease the dosage to 125 mg every 8 h

(D) Discontinue amikacin and switch to gentamicin

(E) Maintain the patient on the present dosage and test auditory function



13. All of the following statements about the clinical uses of the aminoglycosides are accurate EXCEPT

(A) Effective in the treatment of infections caused by Bacteroides fragilis

(B) Gentamicin is used with ampicillin for synergistic effects in the treatment of enterococcal endocarditis

(C) Netilmicin is more likely to be effective than streptomycin in the treatment of a hospital-acquired infection caused by Serratia marcescens

(D) Often used in combination with cephalosporins in the empiric treatment of life-threatening bacterial infections

(E) Owing to their polar nature, aminoglycosides are not absorbed after oral administration


14. Which statement is accurate regarding the antibacterial action of gentamicin?


(A) Antibacterial activity is often reduced by the presence of an inhibitor of cell wall synthesis

(B) Antibacterial action is not concentration-dependent 

(C) Antibacterial action is time-dependent

(D) Efficacy is directly proportional to the duration of time that the plasma level is greater than the minimal inhibitory concentration

(E) Gentamicin continues to exert antibacterial effects even after plasma levels decrease below detectable levels


15. An adult patient (weight 60 kg) has bacteremia suspected to be due to a gram-negative rod. Tobramycin is to be administered using a once-daily dosing regimen, and the loading dose must be calculated to achieve a peak plasma level of 20 mg/L. Assume that the patient has normal renal function. Pharmacokinetic parameters of tobramycin in this patient are as follows: Vd = 20 L; t1/2 = 3 h; CL = 80 mL/min. What loading dose should be given?

(A) 100 mg

(B) 200 mg

(C) 400 mg

(D) 600 mg

(E) 800 mg


16. A 67-year-old man is seen in a hospital emergency department complaining of pain in and behind the right ear. Physical examination shows edema of the external otic canal with purulent exudate and weakness of the muscles on the right side of the face. The patient informs the physician that he is a diabetic. Gram stain of the exudate from the ear shows many polymorphonucleocytes and gram-negative rods, and samples are sent to the microbiology laboratory for culture and drug susceptibility testing. A preliminary diagnosis is made of external otitis. At this point, which of the following is most appropriate?


(A) Amikacin should be administered by intramuscular injection, and the patient should be sent home

(B) Analgesics should be prescribed for pain, but antibiotics should be withheld pending the results of cultures

(C) Oral cefaclor should be prescribed together with analgesics, and the patient should be sent home

(D) The patient should be hospitalized and treatment started with gentamicin plus ticarcillin

(E) The patient should be hospitalized and treatment started with intravenous imipenem-cilastatin


17. Regarding the toxicity of aminoglycosides, which statement is accurate?

(A) Gentamicin and tobramycin are the least likely to cause renal damage

(B) Ototoxicity due to amikacin and gentamicin includes vestibular dysfunction that is often irreversible

(C) Ototoxicity is reduced if loop diuretics are used to facilitate aminoglycoside renal excretion

(D) Skin reactions are rare with use of topical neomycin

(E) With traditional dosage regimens, the earliest sign of nephrotoxicity is a reduced blood creatinine


18. This drug has characteristics almost identical to those of gentamicin but has much weaker activity in combination with penicillin against enterococci.

(A) Amikacin

(B) Erythromycin

(C) Netilmicin

(D) Spectinomycin

(E) Tobramycin



19. Your 23-year-old female patient is pregnant and has gonorrhea. The medical history includes anaphylaxis following exposure to amoxicillin. The most appropriate drug to use is

(A) Azithromycin

(B) Cefixime

(C) Ceftriaxone

(D) Ciprofloxacin

(E) Doxycycline



20. Which statement about “once-daily” dosing with aminoglycosides is not accurate?

(A) Convenient for outpatient therapy

(B) Dosage adjustment is less important in renal insufficiency

(C) Less nursing time is required for drug administration

(D) Often less toxic than conventional (multiple) dosing regimens

(E) Underdosing is less of a problem



21. Which of the following antibiotic combinations is inappropriate based on antagonism at the same site of action?


A. Clindamycin and erythromycin.

B. Doxycycline and amoxicillin.

C. Tigecycline and azithromycin.

D. Ciprofloxacin and amoxicillin.




22. Children younger than 8 years of age should not receive tetracyclines because these agents:


A. Cause rupture of tendons.

B. Deposit in tissues undergoing calcification.

C. Do not cross into the cerebrospinal fluid.

D. Can cause aplastic anemia.



23.  A 30-year-old pregnant female has cellulitis caused by MRSA. Which of the following antibiotics would be the most appropriate option for outpatient therapy?


A. Doxycycline.

B. Clindamycin.

C. Quinupristin/dalfopristin.

D. Tigecycline.




24.  A patient is being discharged from the hospital on a 3-week course of clindamycin. Which of the following potential adverse effects should be discussed with her?


A. Hyperbilirubinemia.

B. Nephrotoxicity.

C. Clostridium difficile diarrhea.

D. Pseudotumor cerebri.