$$\text{Therapeutic Index} = \frac{\text{Lowest dose toxic to patient}}{\text{Dose used for therapy}}$$

Question 1

Which of the following best describes the principle of selective toxicity in antimicrobial therapy?

Accepted Answer

The drug causes greater harm to microbes than to the human host by interfering with microbial structures not present in humans.

Question 2

A patient is prescribed penicillin G for a bacterial infection. Which property makes penicillin G particularly safe for human use?

Accepted Answer

It interferes with cell wall synthesis, a process absent in human cells, resulting in a high therapeutic index.

Question 3

Which equation correctly represents the calculation of the therapeutic index for an antimicrobial medication?

Accepted Answer

$$	ext{Therapeutic Index} = \frac{	ext{Lowest dose toxic to patient}}{	ext{Dose used for therapy}}$$

Question 4

Which of the following mechanisms is responsible for the action of sulfonamides (sulfa drugs) in bacterial cells?

Accepted Answer

Sulfonamides act as competitive inhibitors of the enzyme that binds para-aminobenzoic acid (PABA), blocking folate biosynthesis.

Question 5

A laboratory technician performs a Kirby-Bauer disc diffusion test. What does the zone of inhibition around an antibiotic disc indicate?

Accepted Answer

The area where the antibiotic has killed or inhibited bacterial growth.

Question 6

Which of the following statements about broad-spectrum antibiotics is correct?

Accepted Answer

They affect a wide range of bacteria and are useful in acute, life-threatening situations when the pathogen is unknown.

Question 7

Which mechanism of acquired resistance allows bacteria to rapidly remove antimicrobial drugs from the cell?

Accepted Answer

Increased elimination via efflux pumps

Question 8

Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to β-lactam antibiotics due to which of the following?

Accepted Answer

Production of altered penicillin-binding proteins (PBPs) that β-lactam antibiotics cannot bind to.

Question 9

Which of the following drugs is used topically due to its toxicity and interferes with the transport of peptidoglycan precursors across the membrane?

Accepted Answer

Bacitracin

Question 10

Which of the following is a major reason why antiviral medications are more difficult to develop than antibacterial medications?

Accepted Answer

Viruses rely on host cell metabolic machinery, making selective toxicity challenging.

Question 11

A patient with a C. difficile infection is prescribed fidaxomicin. What is the primary mechanism of action of this drug?

Accepted Answer

It binds to RNA polymerase and interferes with transcription.

Question 12

Which of the following statements about combination therapy for tuberculosis is correct?

Accepted Answer

Combination therapy decreases the chance of developing resistant mutants.

Question 13

Which of the following antibiotics acts by inhibiting DNA gyrase, an enzyme essential for maintaining DNA supercoiling?

Accepted Answer

Fluoroquinolones

Question 14

Which of the following is a correct example of competitive inhibition in antimicrobial action?

Accepted Answer

Sulfonamides compete with PABA for the enzyme involved in folate biosynthesis.

Question 15

Which of the following best explains why Mycoplasma species are intrinsically resistant to penicillin?

Accepted Answer

They lack a cell wall, so penicillin cannot interfere with peptidoglycan synthesis.

Question 16

Which of the following statements about the half-life of an antimicrobial medication is correct?

Accepted Answer

It is the time required for the serum concentration to decrease by 50%.

Question 17

Which of the following mechanisms is NOT a way bacteria acquire resistance to antimicrobial medications?

Accepted Answer

Direct destruction of host immune cells

Question 18

Which of the following is a plausible consequence of broad-spectrum antibiotic use?

Accepted Answer

Increased risk of dysbiosis and overgrowth of pathogens like Clostridium difficile.

Question 19

Which of the following antiviral drugs is a nucleoside analog that acts as a chain terminator during viral DNA synthesis?

Accepted Answer

Acyclovir

Question 20

Which of the following best describes the action of aminoglycosides on bacterial ribosomes?

Accepted Answer

They interfere with the initiation of translation and cause the misreading of mRNA.

Antimicrobial Medications: Mechanisms, Spectrum, and Resistance

Study Guide - Practice Questions