KMU Past Paper Practice

Question:

A 54-year-old man receives an adequate dose of a fluoroquinolone for a susceptible bacterial infection. Several hours after the plasma concentration has fallen below the MIC, bacterial growth remains suppressed. Which pharmacodynamic property best explains this observation?

Options:

Correct Answer: Post-antibiotic effect

Explanation: Fluoroquinolones produce a post-antibiotic effect, so bacterial growth may remain suppressed after drug concentration falls below the MIC.

Question:

A patient has community-acquired pneumonia caused by an atypical respiratory pathogen. A fluoroquinolone is considered because the organism lacks the typical extracellular behavior of many bacteria. Which feature of the class best supports activity in this setting?

Options:

Correct Answer: Useful activity against atypical organisms

Explanation: Fluoroquinolones have activity against important atypical respiratory pathogens such as Legionella, Mycoplasma and Chlamydia.

Question:

A microbiology laboratory studies a gram-positive isolate exposed to a fluoroquinolone. DNA replication is disrupted because separation of newly replicated bacterial chromosomes is impaired. Which enzyme is particularly important as a target in many gram-positive organisms?

Options:

Correct Answer: Topoisomerase IV

Explanation: Topoisomerase IV is an important fluoroquinolone target in many gram-positive bacteria and is required for proper separation of replicated chromosomes.

Question:

A 63-year-old diabetic patient develops unexpected fluctuations in blood glucose after starting a fluoroquinolone. No change has been made to the patient’s antidiabetic regimen. Which recognized adverse effect best accounts for this finding?

Options:

Correct Answer: Dysglycemia

Explanation: Some fluoroquinolones can disturb glucose regulation and produce clinically relevant increases or decreases in blood glucose.

Question:

A child with a serious bacterial infection is being evaluated for fluoroquinolone therapy. The clinician considers the benefits but also recognizes a traditional concern regarding use of this class during growth. Which tissue is primarily involved in this concern?

Options:

Correct Answer: Developing articular cartilage

Explanation: Fluoroquinolones have traditionally been used cautiously in growing children because of concern about toxicity to developing cartilage and musculoskeletal tissues.

Question:

A bacterial culture exposed to a fluoroquinolone shows accumulation of abnormal DNA structures and failure of normal replication. Which cellular event is most directly disrupted by inhibition of DNA gyrase?

Options:

Correct Answer: Control of bacterial DNA supercoiling

Explanation: DNA gyrase controls DNA supercoiling during replication; its inhibition disrupts proper DNA handling and contributes to the bactericidal action of fluoroquinolones.

Question:

A 68-year-old patient with reduced renal function requires antibacterial therapy. The clinician reviews the elimination characteristics of individual fluoroquinolones rather than assuming that all members of the class behave identically. Which drug has substantial non-renal elimination?

Options:

Correct Answer: Moxifloxacin

Explanation: Moxifloxacin differs from several other fluoroquinolones because it undergoes substantial non-renal elimination, an important pharmacokinetic distinction.

Question:

A student compares ciprofloxacin, norfloxacin and ofloxacin with later respiratory fluoroquinolones. Which antimicrobial characteristic is most strongly associated with this earlier fluoroquinolone group?

Options:

Correct Answer: Strong aerobic gram-negative activity

Explanation: Earlier fluoroquinolones are particularly recognized for strong activity against aerobic gram-negative organisms, whereas later agents gained greater respiratory gram-positive activity.

Question:

A topical antibacterial preparation is selected because local treatment is required without relying on systemic absorption. The active agent belongs to the sulfonamide group. How should this preparation be classified?

Options:

Correct Answer: Topical sulfonamide

Explanation: Sulfonamides may be classified as systemically absorbed, poorly absorbed or topical according to how and where they are used.

Question:

A susceptible bacterium is exposed to sulfamethoxazole. The drug competes with a normal bacterial metabolite during folate synthesis. Which structural relationship is responsible for this competitive action?

Options:

Correct Answer: Analogy to para-aminobenzoic acid

Explanation: Sulfonamides resemble PABA structurally and therefore compete with it at dihydropteroate synthase during bacterial folate synthesis.

Question:

A bacterium remains susceptible to the target-enzyme action of a sulfonamide, but laboratory testing shows that little drug accumulates inside the organism. Which resistance mechanism best fits this finding?

Options:

Correct Answer: Reduced permeability or increased efflux

Explanation: Sulfonamide resistance can result from reduced intracellular drug accumulation through decreased permeability or increased drug efflux.

Question:

A microbiologist compares sulfamethoxazole with trimethoprim in a susceptible organism. After trimethoprim exposure, production of an essential reduced folate cofactor decreases. Which conversion has been directly inhibited?

Options:

Correct Answer: Dihydrofolate to tetrahydrofolate

Explanation: Trimethoprim inhibits bacterial dihydrofolate reductase, preventing conversion of dihydrofolate into tetrahydrofolate.

Question:

A patient receiving trimethoprim develops an increased serum potassium level. Renal function was stable before treatment. Which drug effect most directly contributes to this electrolyte abnormality?

Options:

Correct Answer: Reduced renal potassium excretion

Explanation: Trimethoprim can reduce renal potassium excretion, causing potassium retention and clinically important hyperkalemia in susceptible patients.

Question:

A neonate is inadvertently exposed to a sulfonamide. The pediatrician is concerned that the drug may increase the concentration of unbound bilirubin in plasma. Which pharmacological event produces this risk?

Options:

Correct Answer: Displacement of bilirubin from albumin

Explanation: Sulfonamides can displace bilirubin from albumin, increasing free bilirubin that may enter the immature neonatal brain.

Question:

A patient with G6PD deficiency develops anemia after receiving a sulfonamide. The blood picture is compatible with accelerated destruction of erythrocytes. Which mechanism best explains this susceptibility?

Options:

Correct Answer: Reduced protection from oxidative injury

Explanation: G6PD-deficient erythrocytes have impaired antioxidant protection, making them more vulnerable to sulfonamide-associated oxidative hemolysis.

Question:

A patient taking phenytoin has been stable for months. After a sulfonamide is added, the patient develops nystagmus and unsteadiness. Which property of phenytoin makes this interaction clinically important even when the increase in drug exposure is modest?

Options:

Correct Answer: Narrow therapeutic range

Explanation: Phenytoin has a narrow therapeutic range, so reduced clearance or increased active exposure caused by sulfonamides can readily produce toxicity.

Question:

A laboratory compares bacterial folate synthesis with human folate handling. Sulfonamides can selectively interfere with bacterial metabolism because bacteria perform a step that human cells do not rely on in the same way. Which process provides this selective target?

Options:

Correct Answer: De novo bacterial folate synthesis

Explanation: Bacteria synthesize folate through a pathway involving PABA, providing targets such as dihydropteroate synthase that can be selectively inhibited by sulfonamides.

Question:

A bacterial infection responds poorly to a sulfonamide given alone but responds to trimethoprim-sulfamethoxazole when susceptibility is confirmed. Which pharmacological consequence of using the two drugs together contributes to the greater antibacterial effect?

Options:

Correct Answer: Two successive metabolic steps are inhibited

Explanation: Co-trimoxazole produces sequential blockade of bacterial folate metabolism, giving stronger antibacterial activity than either component alone against susceptible organisms.

Question:

A susceptible organism is exposed to sulfamethoxazole. Folate production falls, followed by impaired formation of compounds needed for bacterial growth. Which downstream cellular process is most directly affected by this folate deficiency?

Options:

Correct Answer: Synthesis of nucleic-acid precursors

Explanation: Tetrahydrofolate derivatives are required for synthesis of nucleic-acid precursors, so folate pathway inhibition interferes with bacterial nucleic-acid production.

Question:

A patient receives an oral fluoroquinolone for a susceptible infection. The clinician aims for adequate peak drug exposure because the antibacterial effect becomes stronger as exposure rises relative to the organism’s susceptibility. Which therapeutic principle is being applied?

Options:

Correct Answer: Concentration-dependent antibacterial activity

Explanation: Fluoroquinolones exhibit concentration-dependent killing, so greater exposure relative to bacterial susceptibility generally produces greater antibacterial activity.