$$TI = \frac{\text{dose toxic to humans}}{\text{minimum effective dose}}$$

Question 1

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

Accepted Answer

The drug should kill or inhibit microbial cells without simultaneously damaging host tissues.

Question 2

Which microorganism is the source of the antibiotic streptomycin?

Accepted Answer

Streptomyces griseus

Question 3

A patient is prescribed a broad-spectrum antibiotic. What is a potential risk associated with this treatment?

Accepted Answer

Disruption of normal flora leading to superinfection

Question 4

Which of the following antibiotics acts by inhibiting peptidoglycan synthesis in bacterial cell walls?

Accepted Answer

Penicillin

Question 5

What is the mechanism of action of aminoglycosides such as streptomycin?

Accepted Answer

They change the shape of the 30S ribosomal subunit, causing misreading of mRNA.

Question 6

Which equation represents the therapeutic index (TI) of an antimicrobial drug?

Accepted Answer

$$TI = \frac{	ext{dose toxic to humans}}{	ext{minimum effective dose}}$$

Question 7

Which of the following is NOT a mechanism by which bacteria acquire resistance to antibiotics?

Accepted Answer

Direct uptake of antibiotics from the environment

Question 8

A patient with tuberculosis is treated with isoniazid. What is the primary target of this drug?

Accepted Answer

Disruption of mycolic acid formation in mycobacterial species

Question 9

Which of the following best explains why antiviral drugs often have higher toxicity to host cells compared to antibacterial drugs?

Accepted Answer

Viruses are obligate intracellular parasites and use host cell machinery for replication.

Question 10

Which of the following is an example of drug synergism?

Accepted Answer

The combined effect of trimethoprim and sulfamethoxazole is greater than the sum of their individual effects.

Question 11

Which test is used to determine the minimal inhibitory concentration (MIC) of an antibiotic?

Accepted Answer

Dilution test

Question 12

A bacterial strain produces beta-lactamase. What is the clinical significance of this enzyme?

Accepted Answer

It inactivates penicillin, rendering the bacteria resistant.

Question 13

Which of the following drugs acts by binding to ergosterol in fungal membranes, causing membrane disruption?

Accepted Answer

Amphotericin B

Question 14

Which of the following is a common side effect of broad-spectrum antibiotic use?

Accepted Answer

Superinfection due to disruption of normal flora

Question 15

Which of the following mechanisms allows bacteria to pump out antibiotics, reducing drug effectiveness?

Accepted Answer

Efflux pumps

Question 16

Which of the following is a reason for the development of antibiotic resistance in bacterial populations?

Accepted Answer

Incomplete completion of prescribed antibiotic regimens

Question 17

Which of the following drugs inhibits DNA gyrase in prokaryotes?

Accepted Answer

Ciprofloxacin

Question 18

A patient is prescribed a combination of amoxicillin and clavulanic acid. What is the role of clavulanic acid in this combination?

Accepted Answer

It inhibits beta-lactamase enzymes, protecting amoxicillin from degradation.

Question 19

Which of the following is a correct statement about the Kirby-Bauer disk diffusion test?

Accepted Answer

It measures the zone of inhibition to determine the sensitivity of an organism to an antibiotic.

Question 20

Which of the following is a metabolic antagonist that blocks folic acid synthesis in bacteria?

Accepted Answer

Sulfanilamide

Antimicrobial Drugs: Principles, Sources, and Selective Toxicity

Study Guide - Practice Questions