Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1281: A 9-year-old boy diagnosed with uncomplicated pulmonary tuberculosis is being treated at home with isoniazid, rifampin, and ethambutol after initial hospital treatment. Which statement is accurate for this scenario?

A. His 3-year-old sibling should receive isoniazid prophylaxis. (Correct Answer)
B. A baseline test of auditory function is essential before drug treatment is initiated.
C. Polyarthralgia is a potential adverse effect of the drugs the boy is taking.
D. His mother, who takes care of him, does not need isoniazid prophylaxis.

Explanation: ### Explanation **1. Why Option A is Correct:** In Tuberculosis management, **Chemoprophylaxis** is a critical preventive strategy. According to the National Tuberculosis Elimination Program (NTEP) and WHO guidelines, all household contacts of a pulmonary TB patient who are **under 6 years of age** must receive Isoniazid (INH) prophylaxis (5 mg/kg for 6 months), provided active TB is ruled out. This is because young children are at a high risk of developing severe forms of the disease, such as miliary TB or TB meningitis, following exposure. **2. Why the Other Options are Incorrect:** * **Option B:** Auditory function testing is required for patients receiving **Aminoglycosides** (like Streptomycin). The boy is on Isoniazid, Rifampin, and Ethambutol, none of which are primarily ototoxic. * **Option C:** Polyarthralgia is a classic side effect of **Pyrazinamide** (due to hyperuricemia). Since the boy is only taking Isoniazid, Rifampin, and Ethambutol, this side effect is unlikely. * **Option D:** While the mother is an adult, modern guidelines (including the expanded scope of Latent TB Infection management) emphasize that all close household contacts of a bacteriologically confirmed case should be screened. However, the mandatory requirement for prophylaxis is most strictly defined for the pediatric age group (<6 years), making Option A the most accurate clinical priority. **3. NEET-PG High-Yield Pearls:** * **Ethambutol:** The only bacteriostatic drug in the first-line regimen; its main side effect is **Retrobulbar Neuritis** (monitor visual acuity and red-green color perception). * **Rifampin:** Potent inducer of Cytochrome P450; causes harmless orange-red discoloration of urine and secretions. * **Isoniazid:** Can cause peripheral neuropathy (prevented by **Pyridoxine/Vit B6**) and drug-induced hepatitis. * **Pediatric Dosing:** Ethambutol is now used in children across all weight bands in the intensive phase of treatment.

Question 1282: Quinine given to a patient with falciparum malaria caused sweating and palpitation. What is the likely cause of these symptoms?

A. Cinchonism
B. Hyperglycemia
C. Hypoglycemia (Correct Answer)
D. Hypokalemia

Explanation: ### Explanation The correct answer is **Hypoglycemia**. **1. Mechanism of the Correct Answer:** Quinine is a potent stimulator of the **pancreatic beta cells**, leading to the hypersecretion of insulin (hyperinsulinemia). This often results in profound hypoglycemia. In patients with severe *Falciparum* malaria, this effect is compounded because the malaria parasites themselves consume host glucose, and the infection often leads to depleted hepatic glycogen stores. Symptoms like **sweating, palpitations, tachycardia, and anxiety** are classic sympathoadrenal responses to low blood sugar. **2. Why the Other Options are Incorrect:** * **A. Cinchonism:** This is a dose-dependent toxicity of quinine characterized by tinnitus, high-frequency hearing loss, dizziness, and visual disturbances. While common, it does not typically present with sweating and palpitations. * **B. Hyperglycemia:** Quinine causes the opposite effect (hypoglycemia) due to insulin release. * **D. Hypokalemia:** While some antimalarials can affect electrolytes, hypokalemia is not a classic or direct side effect of quinine therapy and does not explain the specific autonomic symptoms described. **3. High-Yield NEET-PG Pearls:** * **Drug of Choice:** Quinine was traditionally the drug of choice for cerebral malaria, but it has been replaced by **Artesunate** (IV) due to better efficacy and safety profiles. * **Blackwater Fever:** A rare but severe reaction to quinine involving massive intravascular hemolysis and hemoglobinuria. * **QT Prolongation:** Quinine has class 1a antiarrhythmic properties and can cause QT interval prolongation (Torsades de Pointes). * **Pregnancy:** Quinine is considered safe in all trimesters of pregnancy for severe malaria, but blood glucose monitoring is mandatory due to the high risk of hypoglycemia in pregnant women.

Question 1283: Which of the following aminoglycosides has the highest nephrotoxicity?

A. Paromomycin
B. Streptomycin
C. Amikacin
D. Neomycin (Correct Answer)

Explanation: **Explanation:** Aminoglycosides are notorious for their dose-dependent **nephrotoxicity** and **ototoxicity**. The mechanism of nephrotoxicity involves the accumulation of the drug in the proximal renal tubular cells, leading to acute tubular necrosis (ATN). **Why Neomycin is the correct answer:** Among all aminoglycosides, **Neomycin** is the most nephrotoxic. Its potential for systemic toxicity is so high that it is **never administered parenterally**. It is restricted to topical applications (skin/eye) or oral administration for local action within the gut (e.g., hepatic coma or bowel preparation), as it is poorly absorbed from the GI tract. **Analysis of other options:** * **Paromomycin:** Primarily used for intestinal amoebiasis and leishmaniasis. While toxic, it does not exceed the systemic toxicity profile of Neomycin. * **Streptomycin:** Notably the **least nephrotoxic** aminoglycoside but carries a high risk of vestibulotoxicity (ototoxicity). * **Amikacin:** A broad-spectrum aminoglycoside used for multidrug-resistant Gram-negative infections. It has moderate nephrotoxicity, generally less than Neomycin or Gentamicin. **NEET-PG High-Yield Pearls:** 1. **Order of Nephrotoxicity:** Neomycin > Gentamicin > Tobramycin > Amikacin > Streptomycin (Least). 2. **Order of Ototoxicity:** * *Vestibulotoxicity:* Streptomycin and Gentamicin. * *Cochleotoxicity:* Neomycin, Amikacin, and Kanamycin. 3. **Mechanism:** Aminoglycosides inhibit protein synthesis by binding to the **30S ribosomal subunit**. 4. **Clinical Sign:** The earliest sign of aminoglycoside-induced nephrotoxicity is a decrease in **urinary concentrating capacity** (low specific gravity).

Question 1284: A patient developed Achilles tendonitis and leg swelling after taking a certain antibiotic. This adverse effect is commonly associated with fluoroquinolones. What is the most likely mechanism of action of the drug involved?

A. Inhibition of bacterial DNA gyrase and topoisomerase IV (Correct Answer)
B. Inhibition of bacterial cell wall synthesis
C. Inhibition of bacterial folic acid synthesis
D. Inhibition of bacterial protein synthesis at 50S subunit

Explanation: ***Inhibition of bacterial DNA gyrase and topoisomerase IV*** - This is the characteristic mechanism of action for **fluoroquinolones** (e.g., ciprofloxacin, levofloxacin), which disrupts bacterial DNA replication and repair, leading to cell death. - This class of antibiotics is well-known for causing **tendinopathy** and **tendon rupture**, with the **Achilles tendon** being the most commonly affected site, as described in the clinical scenario. *Inhibition of bacterial protein synthesis at 50S subunit* - This mechanism is characteristic of antibiotic classes like **macrolides** (e.g., erythromycin, azithromycin) and **lincosamides** (e.g., clindamycin). - Their common adverse effects include **gastrointestinal distress** and **QT interval prolongation** (macrolides), not tendonitis. *Inhibition of bacterial folic acid synthesis* - This is the mechanism of action for **sulfonamides** (inhibiting dihydropteroate synthase) and **trimethoprim** (inhibiting dihydrofolate reductase). - These drugs are associated with adverse effects like **hypersensitivity reactions** (including Stevens-Johnson syndrome), **photosensitivity**, and **crystalluria**, not tendon-related issues. *Inhibition of bacterial cell wall synthesis* - This mechanism is used by a broad range of antibiotics, including **beta-lactams** (penicillins, cephalosporins) and **glycopeptides** (vancomycin). - Common adverse effects associated with these drugs are **hypersensitivity reactions** (beta-lactams) and **Red Man Syndrome** or **nephrotoxicity** (vancomycin).

Question 1285: Which of the following drug dosages is incorrect for the treatment of leprosy in adults?

A. Clofazimine 50 mg
B. Dapsone 100 mg
C. Rifampicin 450 mg (Correct Answer)
D. Clofazimine 300 mg

Explanation: ***Rifampicin 450 mg*** - The standard dose of Rifampicin for leprosy treatment in adults is **600 mg once monthly** (supervised dose) as per WHO MDT regimen - 450 mg is an incorrect dosage and not part of the recommended treatment protocol - This makes it the correct answer to this negation question *Clofazimine 50 mg* - This is the correct **daily self-administered dose** of Clofazimine in Multibacillary (MB) leprosy - Used as part of the WHO MDT-MB regimen *Dapsone 100 mg* - This is the correct **daily dose** of Dapsone for both Paucibacillary (PB) and Multibacillary (MB) leprosy - Standard component of WHO MDT regimen *Clofazimine 300 mg* - This is the correct **monthly supervised dose** of Clofazimine in Multibacillary (MB) leprosy - Given once a month under supervision as part of WHO MDT-MB regimen

Question 1286: A patient with penicillin allergy presents with fever, burning micturition, and hearing problems accompanied by dizziness. Which drug is the most appropriate for the management?

A. Ciprofloxacin (Correct Answer)
B. Ampicillin-Clavulanic acid
C. Amikacin
D. Azithromycin

Explanation: ***Ciprofloxacin***- Ciprofloxacin is a **fluoroquinolone** that provides excellent coverage against common **uropathogens** (like *E. coli*) and is the preferred choice for managing complicated UTIs in patients with a **penicillin allergy**.- It is the most appropriate choice because, unlike aminoglycosides, it does not carry a high risk of **ototoxicity** or **vestibulotoxicity**, which is crucial as the patient already presents with hearing problems and dizziness.*Azithromycin*- Azithromycin is a **macrolide** that is generally not the first-line empirical antibiotic for typical urinary tract infections (UTIs) due to higher resistance rates among common uropathogens.- While safe in penicillin allergy, its primary spectrum targets atypical pathogens, making it less suitable than Ciprofloxacin for suspected UTIs complicated by fever.*Amikacin*- Amikacin is an **aminoglycoside** known to cause significant **ototoxicity** (leading to hearing loss) and **vestibulotoxicity** (causing dizziness and imbalance).- Given the patient already presents with hearing problems and dizziness, administering Amikacin is **absolutely contraindicated** as it would severely worsen these existing neurotoxic symptoms.*Ampicillin-Clavulanic acid*- This combination includes **Ampicillin**, which belongs to the **penicillin** class of antibiotics.- It is strictly contraindicated because the patient has a confirmed history of **penicillin allergy**, risking a potentially severe, life-threatening hypersensitivity reaction.

Question 1287: Which anti-tubercular drug is associated with mutations in the katG gene?

A. Moxifloxacin
B. Isoniazid (Correct Answer)
C. Ethambutol
D. Rifampicin

Explanation: ***Isoniazid*** - It is a **prodrug** that requires activation by the **catalase-peroxidase enzyme** complex, which is encoded by the **katG gene** in *Mycobacterium tuberculosis*. - Mutations or deletions in the **katG gene** are the most common cause of high-level Isoniazid resistance, preventing the drug from converting into its active form (isonicotinic acyl radical). *Rifampicin* - Resistance is predominantly caused by mutations in the **rpoB gene**, which encodes the **beta-subunit of RNA polymerase**. - Mutations in **rpoB** prevent Rifampicin from binding to the RNA polymerase, thereby inhibiting its primary mechanism of blocking transcription. *Moxifloxacin* - This drug belongs to the fluoroquinolone class and targets **DNA gyrase** (encoded by *gyrA* and *gyrB*) and **topoisomerase IV**. - Resistance is typically mediated by point mutations within the **Quinolone Resistance Determining Regions (QRDRs)** of these target genes. *Ethambutol* - Resistance to Ethambutol is most frequently associated with mutations in the **embB gene**. - The **embB gene** encodes the **arabinosyl transferase** enzyme, which is crucial for synthesizing the **arabinogalactan layer** of the mycobacterial cell wall.

Question 1288: Which of the following is a first-line antitubercular drug prescribed in the initial 2 months of treatment?

A. Streptomycin
B. Linezolid
C. Levofloxacin
D. Ethambutol (Correct Answer)

Explanation: **Ethambutol** - **Ethambutol (E)** is a crucial component of the standard **four-drug regimen (RIPE)** used during the intensive initial phase (first 2 months) of active TB treatment. - Its primary function is to prevent emerging **rifampicin** or **isoniazid resistance**, although its main adverse effect is dose-related **optic neuritis**. *Streptomycin* - Streptomycin is an **aminoglycoside** and was historically used, but it is currently classified as a **second-line injectable agent** due to its toxicity and need for parenteral administration. - It is typically reserved for treating **multidrug-resistant TB (MDR-TB)** or in situations where oral first-line drugs cannot be used. *Linezolid* - Linezolid is an **oxazolidinone** antibiotic primarily reserved for treating highly resistant forms of TB, specifically **MDR-TB** or **XDR-TB**. - It is not included in the standard first-line regimen due to concerns regarding side effects like **myelosuppression** and **peripheral neuropathy**. *Levofloxacin* - Levofloxacin is a **fluoroquinolone** antibiotic, which is classified as a **second-line antitubercular agent**. - It is generally used in alternative regimens or for treating **drug-resistant TB** when standard first-line drugs are ineffective or contraindicated.

Question 1289: Which of the following antimicrobial agents acts by inhibiting bacterial cell wall synthesis through binding to penicillin-binding proteins (PBPs)?

A. Penicillin (Correct Answer)
B. Gentamicin
C. Ciprofloxacin
D. Tetracycline

Explanation: ***Penicillin*** - **Penicillins** are β-lactam antibiotics that act by **covalently binding** to and inhibiting **Penicillin-Binding Proteins (PBPs)** (transpeptidases) [1], [2]. - This inhibition prevents the cross-linking of **peptidoglycan strands**, leading to a faulty, unstable bacterial cell wall and eventual cell lysis (bactericidal action) [1], [2]. *Gentamicin* - Gentamicin is an **aminoglycoside** antibiotic whose main mechanism of action is inhibiting **bacterial protein synthesis** by binding to the **30S ribosomal subunit**. - It causes misreading of the mRNA template, leading to the incorporation of incorrect amino acids and production of non-functional proteins. *Tetracycline* - Tetracyclines are bacteriostatic antibiotics that inhibit **protein synthesis** by reversibly binding to the **30S ribosomal subunit**. - This binding prevents the attachment of **aminoacyl-tRNA** to the A site on the ribosome. *Ciprofloxacin* - Ciprofloxacin is a **fluoroquinolone** that interferes with **DNA replication and transcription** by inhibiting essential bacterial enzymes. - It primarily targets **DNA gyrase (topoisomerase II)** and **topoisomerase IV**, leading to double-strand DNA breaks and cell death.

Question 1290: Which of the following is the treatment for complicated gonorrhoea due to penicillin-resistant Neisseria gonorrhoeae?

A. Vancomycin
B. Tetracycline
C. Ceftriaxone (Correct Answer)
D. Amoxicillin

Explanation: ***Correct: Ceftriaxone*** - **Ceftriaxone** (a third-generation cephalosporin) is the current cornerstone of treatment for both uncomplicated and complicated gonorrhoea, especially given the high prevalence of **penicillin resistance** in *N. gonorrhoeae*. - For complicated infections (e.g., disseminated gonococcal infection, epididymo-orchitis, pelvic inflammatory disease), it is often given as a higher dose (e.g., 1g IV daily) and sometimes combined with **azithromycin** where co-infection with *Chlamydia* is possible. *Incorrect: Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic and is ineffective due to widespread resistance mediated by **plasmid-encoded beta-lactamases** (e.g., *penicillinase-producing Neisseria gonorrhoeae* or PPNG). - Penicillins are no longer recommended for the treatment of gonorrhoea in any setting because of this high resistance. *Incorrect: Tetracycline* - **Tetracycline** (or doxycycline) was historically used for gonorrhoea treatment but resistance has become common, rendering it unreliable as a first-line therapy. - It is currently used primarily to treat concurrent **Chlamydia trachomatis** infection, rather than gonorrhoea itself. *Incorrect: Vancomycin* - **Vancomycin** is a glycopeptide antibiotic primarily effective against **Gram-positive bacteria** (like MRSA) by interfering with cell wall synthesis. - *Neisseria gonorrhoeae* is a **Gram-negative bacterium**, and vancomycin is not effective for its treatment.

Practice by Chapter

Beta-Lactam Antibiotics

Practice Questions

Aminoglycosides

Practice Questions

Macrolides and Ketolides

Practice Questions

Tetracyclines

Practice Questions

Quinolones

Practice Questions

Sulfonamides and Trimethoprim

Practice Questions

Antimycobacterial Drugs

Practice Questions

Antifungal Agents

Practice Questions

Antiviral Drugs

Practice Questions

Antiparasitic Agents

Practice Questions

Principles of Antimicrobial Selection

Practice Questions

Antimicrobial Resistance

Practice Questions

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