Pharmacology Antimicrobial Therapy Principles Questions and Answers

Question 1

A patient with infective endocarditis caused by Enterococcus faecalis is treated with a combination of ampicillin and gentamicin. What is the primary rationale for using this specific combination?

Accepted Answer

To achieve a synergistic bactericidal effect.

Answer

This is a classic example of antimicrobial synergy. Ampicillin, a beta-lactam, inhibits cell wall synthesis, which increases the permeability of the bacterial cell to the aminoglycoside, gentamicin. This enhanced uptake allows gentamicin to more effectively reach its intracellular target (the 30S ribosome), resulting in a bactericidal effect that is greater than the individual agents alone.

Question 2

A bacterial strain isolated from a wound culture is found to be resistant to ampicillin but susceptible to amoxicillin-clavulanate. What is the most likely mechanism of resistance to ampicillin in this strain?

Accepted Answer

Production of a beta-lactamase enzyme.

Answer

The addition of clavulanate, a beta-lactamase inhibitor, restores the activity of the beta-lactam antibiotic (amoxicillin). This indicates that the bacterium's resistance mechanism is the production of a beta-lactamase enzyme, which inactivates the antibiotic by hydrolyzing the beta-lactam ring.

Question 3

Which of the following best describes the primary pharmacodynamic property of beta-lactam antibiotics, such as piperacillin, which dictates their dosing strategy?

Accepted Answer

Their efficacy is best correlated with the duration that the drug concentration remains above the minimum inhibitory concentration (T > MIC).

Answer

Beta-lactam antibiotics demonstrate time-dependent killing. Their effectiveness is maximized by keeping the drug concentration above the minimum inhibitory concentration (MIC) for as long as possible during the dosing interval (fT > MIC). This principle supports the use of frequent intermittent dosing or continuous infusions to optimize therapeutic outcomes.

Question 4

Sulfonamide antibiotics, such as sulfamethoxazole, exhibit selective toxicity against bacteria. Why are human cells typically unaffected by this mechanism?

Accepted Answer

Human cells utilize pre-formed folic acid from dietary sources.

Answer

Sulfonamides competitively inhibit dihydropteroate synthase, an enzyme essential for the de novo synthesis of folic acid in bacteria. Human cells lack this pathway and instead acquire folic acid from the diet, making them insusceptible to the action of sulfonamides.

Question 5

A physician notes that an aminoglycoside has a significant post-antibiotic effect (PAE). Which of the following statements best describes the clinical implication of the PAE?

Accepted Answer

Bacterial growth suppression continues for a period after the plasma concentration has fallen below the MIC.

Answer

The post-antibiotic effect (PAE) is the phenomenon of persistent suppression of bacterial growth even after the antibiotic concentration has fallen below the minimum inhibitory concentration (MIC). This property, characteristic of drugs like aminoglycosides, allows for less frequent, high-dose administration schedules (once-daily dosing), which can maximize efficacy and minimize certain toxicities.

Pharmacology Practice Test

Pharmacology Practice Test

Pharmacology Antimicrobial Therapy Principles Questions and Answers