KMU Past Paper Practice

Question:

A 28-year-old man is prescribed a tetracycline-class drug that has a long duration of action and is suitable for convenient oral therapy. Which drug best fits this pharmacological classification?

Correct Answer: Doxycycline

Explanation: Doxycycline is a long-acting tetracycline. Tetracycline is shorter acting, while demeclocycline has an intermediate duration of action.

Question:

A laboratory compares the effect of two 30S ribosomal inhibitors. Drug X suppresses multiplication without extensive bacterial death, whereas Drug Y rapidly kills susceptible organisms. Which difference best accounts for these observations?

Correct Answer: Drug X reversibly inhibits translation while Drug Y causes faulty protein synthesis

Explanation: Tetracyclines reversibly inhibit protein-chain elongation and are mainly bacteriostatic, whereas aminoglycosides cause abnormal protein synthesis and bactericidal injury.

Question:

A student classifies antibacterial protein-synthesis inhibitors according to their principal ribosomal target. Which group contains drugs acting predominantly on the 50S rather than the 30S subunit?

Correct Answer: Macrolides and chloramphenicol

Explanation: Macrolides and chloramphenicol are 50S inhibitors. Tetracyclines and aminoglycosides principally target the bacterial 30S subunit.

Question:

A patient taking an oral tetracycline separates the medicine from his antacid but continues taking it with an iron preparation. His antibacterial response remains suboptimal. Which additional substance would be expected to produce a similar pharmacokinetic problem?

Correct Answer: Calcium-containing dairy product

Explanation: Calcium, like iron, can form poorly absorbed complexes with tetracyclines. The shared mechanism is interaction with multivalent metal ions in the gut.

Question:

A 21-year-old woman taking minocycline for acne reports dizziness and a sensation that the room is moving. Her hearing is preserved and serum creatinine is normal. Which characteristic adverse effect best accounts for her symptoms?

Correct Answer: Vestibular disturbance

Explanation: Minocycline is particularly associated with vestibular adverse effects such as dizziness, vertigo and impaired balance.

Question:

A patient develops painful swallowing shortly after starting doxycycline. He reports taking the tablet immediately before lying down at night. Which adverse effect most appropriately explains this presentation?

Correct Answer: Medication-related esophageal irritation

Explanation: Doxycycline can irritate the esophageal mucosa when a tablet remains in prolonged contact with it, producing painful swallowing or esophagitis.

Question:

Two bacterial strains are exposed to the same concentration of tetracycline. Both accumulate similar intracellular drug levels, but one strain continues protein synthesis because the drug can no longer effectively interfere with ribosomal function. Which resistance mechanism best explains this finding?

Correct Answer: Ribosomal protection

Explanation: Ribosomal protection proteins allow translation to continue despite adequate intracellular tetracycline, distinguishing this mechanism from reduced entry or efflux.

Question:

A patient treated with a tetracycline has an infection caused by an organism that lacks a typical extracellular lifestyle and survives within host cells. Which additional pathogen group would be expected to share clinically useful susceptibility to this drug class?

Correct Answer: Chlamydiae

Explanation: Tetracyclines have important activity against atypical and intracellular bacteria, including chlamydiae as well as rickettsiae.

Question:

A child is inadvertently exposed to repeated tetracycline therapy while permanent teeth are developing. Several years later, dental examination shows a persistent cosmetic abnormality. Which pharmacological property is responsible?

Correct Answer: Accumulation in calcifying tissues

Explanation: Tetracyclines bind calcium and become incorporated into developing teeth, producing persistent yellow-brown discoloration.

Question:

A microbiologist observes that an aminoglycoside-treated bacterium produces abnormal proteins and subsequently develops progressive membrane dysfunction. Which initial molecular event most directly leads to this sequence?

Correct Answer: Irreversible interference with 30S ribosomal function

Explanation: Aminoglycosides bind the 30S subunit irreversibly, disturb initiation and translation accuracy, and generate abnormal proteins that contribute to bactericidal membrane injury.

Question:

An aminoglycoside-resistant Gram-negative isolate has no detectable drug-modifying enzymes. Drug binding to isolated ribosomes is normal, but intact bacteria accumulate very little antibiotic. Which mechanism best accounts for resistance?

Correct Answer: Reduced bacterial uptake

Explanation: Reduced entry can cause aminoglycoside resistance even when the ribosomal target remains susceptible and drug-modifying enzymes are absent.

Question:

A patient with severe infection receives an aminoglycoside. The drug reaches adequate serum concentrations but achieves poor concentrations in cerebrospinal fluid. Which pharmacokinetic characteristic best explains this finding?

Correct Answer: Limited penetration across tissue barriers

Explanation: Aminoglycosides are highly polar and distribute mainly in extracellular fluid, with poor penetration into sites such as cerebrospinal fluid.

Question:

A clinician selects tobramycin for a serious infection after culture demonstrates a susceptible aerobic Gram-negative bacillus. Which organism characteristic is most important for effective intracellular delivery of this drug?

Correct Answer: Active oxygen-dependent transport

Explanation: Aminoglycoside uptake across the bacterial cytoplasmic membrane requires oxygen-dependent transport, explaining their activity against aerobic rather than anaerobic organisms.

Question:

A patient receiving amikacin develops an increase in serum creatinine during therapy. The drug is stopped and renal function subsequently improves. Which site of drug accumulation most directly explains this toxicity?

Correct Answer: Renal tubular cells

Explanation: Aminoglycosides accumulate in renal tubular cells and can cause tubular injury, producing the characteristic nephrotoxicity of this drug class.

Question:

An aminoglycoside-treated patient develops tinnitus. Review of his medication chart identifies a second drug with known ototoxic potential. Which principle best explains why this combination is concerning?

Correct Answer: Combined exposure can enhance inner-ear toxicity

Explanation: Coadministration of another ototoxic drug can increase the risk of aminoglycoside-related cochlear or vestibular damage.

Question:

Two aminoglycoside regimens produce similar total drug exposure. Regimen X achieves a higher peak concentration, while Regimen Y maintains lower concentrations for a longer period. The organism is susceptible to both. Which regimen characteristic is expected to favor greater initial bacterial killing?

Correct Answer: Higher peak drug concentration

Explanation: Aminoglycosides show concentration-dependent killing, so a higher effective peak concentration produces greater initial bactericidal activity.

Question:

A patient with a susceptible infection receives an aminoglycoside. Several hours after serum concentrations fall substantially, bacterial multiplication remains suppressed. Which additional pharmacodynamic property works together with concentration-dependent killing to produce this prolonged effect?

Correct Answer: Persistent suppression after drug exposure

Explanation: The post-antibiotic effect means bacterial growth remains suppressed after effective drug concentrations decline, complementing concentration-dependent killing.

Question:

A patient has a localized condition for which an aminoglycoside is desired without significant systemic exposure. The clinician selects a drug whose systemic toxicity limits parenteral use and which is therefore mainly used for local or non-systemic purposes. Which drug is most appropriate?

Correct Answer: Neomycin

Explanation: Neomycin has important systemic toxicity and is therefore mainly used for local or other non-systemic purposes rather than routine parenteral therapy.

Question:

A patient with a susceptible serious bacterial infection receives a beta-lactam together with an aminoglycoside. Laboratory testing demonstrates substantially greater killing with the combination. Which sequence best explains the enhanced effect?

Correct Answer: Cell-wall injury → improved aminoglycoside entry → enhanced killing

Explanation: A cell-wall-active drug can facilitate aminoglycoside penetration into susceptible bacteria, producing synergistic antibacterial killing.

Question:

A patient receiving an aminoglycoside has stable antibacterial response initially. Renal function then deteriorates, but the treatment exposure is not adjusted. Which sequence best predicts the resulting pharmacological problem?

Correct Answer: Reduced renal clearance → drug accumulation → greater toxicity

Explanation: Aminoglycosides are eliminated mainly by glomerular filtration. Declining renal function reduces clearance, allowing accumulation and increasing nephrotoxic and ototoxic risk.