Explore foundational chemotherapy principles through a microbiology lens. Learn about antimicrobial mechanisms, drug action, and key concepts relevant for secon
Jan/Apr 2022/23 --- Question 1 Which one of the following antibiotics is likely to be most effective agent in the treatment of an infection due to enterococci if used in conjunction with penicillin G? (Application question) Choices: - A. Streptomycin - B. Amikacin - C. Gentamicin - D. Tobramycin - E. Netilmicin Answer: C. Gentamicin Explanation: Gentamicin, when used in combination with penicillin G, shows synergistic activity against enterococci. The penicillin disrupts the cell wall, allowing better penetration of the aminoglycoside (gentamicin) into the bacterial cell, resulting in enhanced bactericidal activity. --- Question 2 Regarding the antibacterial action of gentamicin, which one of the following statements is the MOST accurate? (Application question) Choices: - A. Antibacterial activity is often reduced by the presence of an inhibitor of cell wall synthesis - B. Efficacy is directly proportionate to the time that the plasma level of the drug is greater than the minimal inhibitory concentration - C. Gentamicin continues to exert antibacterial effects even after plasma levels decrease below detectable levels - D. The antibacterial action of gentamicin is not concentration-dependent - E. The antibacterial action of gentamicin is time-dependent Answer: C. Gentamicin continues to exert antibacterial effects even after plasma levels decrease below detectable levels Explanation: Gentamicin exhibits a post-antibiotic effect (PAE) , meaning it continues to suppress bacterial growth even after drug concentrations fall below the minimum inhibitory concentration (MI C). This is characteristic of concentration-dependent antibiotics like aminoglycosides. --- Question 3 A 24-year-old woman is diagnosed with genital herpes simplex virus infection. Which agent is indicated for use in this diagnosis? Choices: - A. Zanamivir - B. Cidofovir - C. Ganciclovir - D. Valacyclovir Answer: D. Valacyclovir Explanation: Valacyclovir, famciclovir, penciclovir, and acyclovir are all indicated for herpes simplex virus infection. Cidofovir and ganciclovir are used for CMV retinitis. Zanamivir is indicated for influenza. --- Question 4 A 72-year-old man is admitted to the hospital from a nursing home with severe pneumonia. He was discharged from the hospital 1 week ago after open heart surgery. The patient has no known allergies. Which of the following regimens is most appropriate for empiric coverage of methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa in this patient? Choices: - A. Vancomycin + cefepime + ciprofloxacin - B. Vancomycin + cefazolin + ciprofloxacin - C. Telavancin + cefepime + ciprofloxacin - D. Daptomycin + cefepime + ciprofloxacin Answer: A. Vancomycin + cefepime + ciprofloxacin Explanation: Vancomycin provides adequate coverage against MRSA, and cefepime and ciprofloxacin provide adequate empiric coverage of Pseudomonas. Option B is incorrect because cefazolin does not have activity against Pseudomonas. Option C is incorrect because telavancin should be avoided if possible with drugs that prolong the QTc interval (ciprofloxacin). Daptomycin is inactivated by pulmonary surfactant and should not be used for pneumonia. --- Question 5 Select the agent which evades acquired efflux and target-mediated resistance Choices: - A. Tigecycline - B. Minocycline - C. Tetracycline - D. Doxycycline Answer: A. Tigecycline Explanation: Tigecycline is the first glycylcycline to be launched and is one of the very few new antimicrobials with activity against Gram-negative bacteria. It evades acquired efflux and target-mediated resistance to classical tetracyclines, but not chromosomal efflux in Proteeae and Pseudomonas. It has shown equivalence to imipenem/cilastatin in intra-abdominal infections and is useful for treating multiresistant pathogens. --- Question 6 Superinfections are more common with Choices: - A. Use of narrow spectrum antibiotics - B. Use of antibiotics that are completely absorbed from the small intestines - C. Short courses of antibiotics - D. Use of antibiotic combinations covering both gram positive and gram negative bacteria Answer: D. Use of antibiotic combinations covering both gram positive and gram negative bacteria Explanation: Broad-spectrum antibiotics or antibiotic combinations that cover both gram-positive and gram-negative bacteria disrupt the normal flora more extensively, allowing opportunistic organisms (like C. difficile or Candida) to overgrow, leading to superinfections. --- Question 7 Which one of the following drugs is most likely to be effective against multi-drug-resistant (MDR) strains of M tuberculosis, including those resistant to streptomycin? Choices: - A. Spectinomycin - B. Clarithromycin - C. Amikacin - D. Gentamicin - E. Meropenem Answer: C. Amikacin Explanation: Amikacin is an aminoglycoside that is often effective against MDR-TB strains, including those resistant to streptomycin. It is one of the second-line agents used in the treatment of drug-resistant tuberculosis due to its different resistance profile compared to streptomycin. --- Question 8 A 77-year-old woman was started on antibiotics for pneumonia treatment. After 3 days of antibiotic therapy, the serum creatinine doubled. Which of the following antibiotics is most likely responsible for this increase in serum creatinine? Choices: - A. Doxycycline - B. Tobramycin - C. Linezolid - D. Clarithromycin Answer: B. Tobramycin Explanation: Aminoglycosides such as tobramycin accumulate in the proximal tubular cells of the kidney and disrupt calcium-mediated transport processes. This results in kidney damage ranging from mild, reversible renal impairment to severe, potentially irreversible acute tubular necrosis. Nephrotoxicity is not commonly associated with tetracyclines, macrolides, or oxazolidinones. --- Question 9 The persistent suppression of bacterial growth that may occur following limited exposure to some antimicrobial drugs is called Choices: - A. Concentration-dependent killing - B. Sequential blockade - C. Clinical synergy - D. The post antibiotic effect - E. Time-dependent killing Answer: D. The post antibiotic effect Explanation: The post-antibiotic effect (PAE) is the continued suppression of bacterial growth after brief exposure to an antimicrobial agent, even after drug concentrations have fallen below the MIC. This is particularly notable with aminoglycosides and fluoroquinolones. --- Question 10 Select the antibiotic whose dose must be reduced in patients with renal insufficiency Choices: - A. Ampicillin - B. Erythromycin - C. Chloramphenicol - D. Tobramycin - E. Isoniazid Answer: D. Tobramycin Explanation: Tobramycin (an aminoglycoside) is primarily eliminated by the kidneys through glomerular filtration. In patients with renal insufficiency, the drug can accumulate to toxic levels, so dose adjustment is necessary to prevent nephrotoxicity and ototoxicity. --- Question 11 Isoniazid is a primary antitubercular agent that Choices: - A. May discolor the tears, saliva, urine or feces orange-red - B. May be ototoxic and nephrotoxic - C. Requires pyridoxine supplementation - D. Causes ocular complications that are reversible if the drug is discontinued - E. Should never be used due to hepatotoxic potential Answer: C. Requires pyridoxine supplementation Explanation: Isoniazid can cause peripheral neuropathy by interfering with pyridoxine (vitamin B6) metabolism. Pyridoxine supplementation is given to prevent this adverse effect, especially in high-risk patients (diabetics, alcoholics, malnourished individuals, pregnant women). --- Question 12 Linezolid would be a good choice for antibiotic treatment in which of the following patient scenarios? Choices: - A. Bacteremia caused by Staphylococcus aureus - B. Urinary tract infection caused by Escherichia coli - C. Diabetic foot infection caused by Pseudomonas aeruginosa - D. Pneumonia caused by drug-resistant Streptococcus pneumoniae Answer: D. Pneumonia caused by drug-resistant Streptococcus