Antimicrobial Agents — MCQs
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A 50-year-old HIV-seropositive male presented to the emergency room with multiple episodes of generalized tonic-clonic seizures. The patient is not on highly active antiretroviral therapy. The CD4 count was 45/μL. On examination, the patient was mildly arousable and disoriented, with no nuchal rigidity or focal neurological deficits. Gadolinium-enhanced magnetic resonance imaging and magnetic resonance spectroscopy were conducted. Which is the most appropriate drug to be given in this condition?
Which of the following statements about isavuconazonium sulfate is false?
Which of the following anti-TB drugs acts on extracellular organisms and is a bactericidal drug?
What is the treatment of choice for a gonococcal infection that is resistant to penicillin?
Which antifungal agent can be used orally but not intravenously?
Which of the following antibiotics is least effective against anaerobic streptococci?
What is the prophylactic drug of choice for diphtheria?
Which of the following drugs is ineffective in treating infections caused by Bacteroides fragilis?
Which of the following statements about cephalosporins is false?
Which of the following drugs is an antipseudomonal penicillin?
Antimicrobial Agents Indian Medical PG Practice Questions and MCQs
Question 1601: A 50-year-old HIV-seropositive male presented to the emergency room with multiple episodes of generalized tonic-clonic seizures. The patient is not on highly active antiretroviral therapy. The CD4 count was 45/μL. On examination, the patient was mildly arousable and disoriented, with no nuchal rigidity or focal neurological deficits. Gadolinium-enhanced magnetic resonance imaging and magnetic resonance spectroscopy were conducted. Which is the most appropriate drug to be given in this condition?
- A. Caspofungin
- B. Streptokinase
- C. Pyrimethamine + Sulphadiazine (Correct Answer)
- D. Voriconazole
Explanation: ***Pyrimethamine + Sulphadiazine*** - The patient's presentation with new-onset **generalized tonic-clonic seizures**, severe **immunocompromise (CD4 count 45/μL)**, and characteristic imaging findings (though not fully described, strongly suggestive of toxoplasmosis in this context) points to **cerebral toxoplasmosis**. - **Pyrimethamine combined with sulphadiazine** is the **first-line treatment** for cerebral toxoplasmosis, an opportunistic infection common in HIV patients with advanced immunosuppression. *Caspofungin* - **Caspofungin** is an **echinocandin antifungal agent** primarily used to treat invasive fungal infections, such as candidiasis and aspergillosis. - It has no activity against **Toxoplasma gondii**, which is a protozoan parasite, not a fungus. *Streptokinase* - **Streptokinase** is a **thrombolytic agent** used to dissolve blood clots in conditions like myocardial infarction and pulmonary embolism. - It has no role in the management of neurologic infections or seizures in an HIV-positive patient, as it does not address the underlying **pathogen**. *Voriconazole* - **Voriconazole** is a **broad-spectrum triazole antifungal agent** effective against various fungal infections, including aspergillosis and candidiasis. - While it is an antifungal, it is not indicated for treating **Toxoplasma gondii** infection, which is a parasitic infection.
Question 1602: Which of the following statements about isavuconazonium sulfate is false?
- A. Effective against yeasts, molds, and dimorphic fungi
- B. Has minimal nephrotoxicity
- C. Acts through blocking cytoplasmic proteins (Correct Answer)
- D. Approved for aspergillosis and mucormycosis
Explanation: ***Acts through blocking cytoplasmic proteins*** - Isavuconazonium sulfate, an azole antifungal, primarily acts by **inhibiting lanosterol 14-α-demethylase (CYP51)**, an enzyme crucial for fungal ergosterol synthesis. - This **disrupts fungal cell membrane integrity**, rather than blocking cytoplasmic proteins. - This is the **FALSE statement** - the mechanism is membrane-directed, not cytoplasmic protein-directed. *Effective against yeasts, molds, and dimorphic fungi* - Isavuconazonium sulfate is a **broad-spectrum triazole antifungal** effective against a wide range of fungal pathogens. - This includes common yeasts like *Candida* species, molds such as *Aspergillus* and *Rhizopus*, and various dimorphic fungi. *Approved for aspergillosis and mucormycosis* - This statement is true; isavuconazonium sulfate is indeed **FDA-approved for the treatment of invasive aspergillosis and mucormycosis**. - It provides an important therapeutic option for these serious and often life-threatening fungal infections. *Has minimal nephrotoxicity* - Isavuconazonium sulfate is notable for its **favorable renal safety profile** compared to amphotericin B and lacks the cyclodextrin vehicle present in IV voriconazole. - Studies have shown a **low incidence of nephrotoxicity**, making it a preferred choice in patients with impaired renal function or those at risk of kidney injury.
Question 1603: Which of the following anti-TB drugs acts on extracellular organisms and is a bactericidal drug?
- A. Isoniazid
- B. Streptomycin (Correct Answer)
- C. Ethambutol
- D. Rifampicin
Explanation: ***Streptomycin*** - Streptomycin is an **aminoglycoside antibiotic** that acts primarily on **extracellular, rapidly multiplying *Mycobacterium tuberculosis***. - It is a **bactericidal drug** that inhibits protein synthesis by binding to the 30S ribosomal subunit. *Isoniazid* - While **highly bactericidal**, isoniazid primarily targets **intracellular** and rapidly growing *M. tuberculosis* by inhibiting **mycolic acid synthesis**. - Its activity is prominent against **intracellular organisms** found within macrophages. *Ethambutol* - Ethambutol is a **bacteriostatic drug** that prevents the formation of the **mycobacterial cell wall** by inhibiting arabinosyl transferase. - It works against both **extracellular and intracellular organisms** but is not the most potent bactericidal drug against extracellular forms. *Rifampicin* - Rifampicin is a **bactericidal drug** that inhibits **RNA synthesis** by binding to DNA-dependent RNA polymerase. - It is effective against both **extracellular and intracellular organisms** but also has good sterilizing activity against dormant bacilli, unlike streptomycin which is primarily extracellular.
Question 1604: What is the treatment of choice for a gonococcal infection that is resistant to penicillin?
- A. Penicillin
- B. Ceftazidime
- C. Ceftriaxone (Correct Answer)
- D. Spectinomycin
Explanation: ***Ceftriaxone*** - **Ceftriaxone** is the recommended first-line treatment for uncomplicated gonococcal infections, especially given increasing resistance to other antibiotics like penicillin. - It is a **third-generation cephalosporin** that targets the bacterial cell wall synthesis effectively. *Penicillin* - **Penicillin** is no longer the recommended treatment for gonorrhea due to widespread resistance, primarily mediated by **beta-lactamase production** by *Neisseria gonorrhoeae*. - Treating with penicillin when resistance is present would lead to treatment failure and continued transmission. *Ceftazidime* - **Ceftazidime** is a third-generation cephalosporin with activity against gram-negative organisms. - However, its activity against *Neisseria gonorrhoeae* is not considered first-line or superior to ceftriaxone, which has better pharmacokinetic properties for treating gonorrhea. *Spectinomycin* - **Spectinomycin** is an alternative treatment for gonococcal infections, particularly in individuals with severe allergy to cephalosporins or in regions where ceftriaxone resistance is emerging. - However, it is not the treatment of choice in regions where ceftriaxone is effective and available.
Question 1605: Which antifungal agent can be used orally but not intravenously?
- A. Terbinafine (Correct Answer)
- B. Fluconazole
- C. Amphotericin B
- D. Voriconazole
Explanation: ***Terbinafine*** - Terbinafine is an **allylamine antifungal** primarily used to treat **dermatophyte infections** (e.g., onychomycosis, tinea infections). - It is highly effective when administered **orally** with excellent tissue penetration. - **Not available in IV formulation** - only oral and topical forms exist for clinical use. *Fluconazole* - Fluconazole is a triazole antifungal available in **both oral and intravenous** formulations. - Commonly used for candidiasis, cryptococcal meningitis, and prophylaxis in immunocompromised patients. *Voriconazole* - Voriconazole is a broad-spectrum triazole antifungal available in **both oral and intravenous** formulations. - Used for invasive fungal infections such as **invasive aspergillosis** and resistant Candida species. *Amphotericin B* - Amphotericin B is primarily administered **intravenously** for severe, systemic fungal infections. - While an oral formulation exists for intestinal candidiasis, systemic absorption from the GI tract is negligible, making it unsuitable for systemic treatment via oral route.
Question 1606: Which of the following antibiotics is least effective against anaerobic streptococci?
- A. Carbenicillin (Correct Answer)
- B. Vancomycin
- C. Clindamycin
- D. Penicillin
Explanation: ***Correct: Carbenicillin*** - **Carbenicillin** is an extended-spectrum penicillin (carboxypenicillin) developed primarily for **Gram-negative bacteria**, especially **Pseudomonas aeruginosa**. - While it has some activity against certain anaerobes, it has the **least activity against anaerobic streptococci** compared to the other options listed. - Its clinical use was mainly for **Gram-negative infections**, and it has been largely replaced by piperacillin and ticarcillin due to better pharmacokinetics. - Among the listed antibiotics, carbenicillin is the **least reliable choice** for treating anaerobic streptococcal infections. *Incorrect: Vancomycin* - **Vancomycin** is highly effective against **Gram-positive bacteria**, including **anaerobic streptococci**. - It inhibits **cell wall synthesis** by binding to D-Ala-D-Ala terminals and is a standard agent for serious Gram-positive anaerobic infections. - Excellent activity against **anaerobic Gram-positive cocci**, including Peptostreptococcus species. *Incorrect: Penicillin* - **Penicillin G** is often the **first-line agent** for anaerobic streptococcal infections. - Highly effective against most **anaerobic Gram-positive cocci** due to its ability to disrupt **bacterial cell wall synthesis**. - Remains a gold standard for susceptible anaerobic streptococci, though resistance patterns must be considered. *Incorrect: Clindamycin* - **Clindamycin** is notably effective against a broad range of **anaerobic bacteria**, including **anaerobic streptococci** (Peptostreptococcus species). - Acts by inhibiting **bacterial protein synthesis** at the 50S ribosomal subunit. - Considered one of the **most reliable agents** for anaerobic Gram-positive infections, including those in the oral cavity and respiratory tract.
Question 1607: What is the prophylactic drug of choice for diphtheria?
- A. Tetracycline
- B. Cefaclor
- C. Ceftriaxone
- D. Erythromycin (Correct Answer)
Explanation: ***Erythromycin*** - **Erythromycin** is the recommended drug for post-exposure prophylaxis against **diphtheria** to eliminate carriage of *Corynebacterium diphtheriae*. - It effectively eradicates the bacteria from the **nasopharynx** and skin, preventing disease transmission. *Tetracycline* - While tetracyclines are broad-spectrum antibiotics, they are not the first-line choice for **diphtheria prophylaxis**. - **Doxycycline** may be used as an alternative in some cases but is less preferred than macrolides. *Cefaclor* - **Cefaclor** is a second-generation **cephalosporin** and is not typically used for diphtheria prophylaxis. - **Cephalosporins** are not generally effective against *Corynebacterium diphtheriae* carriage. *Ceftriaxone* - **Ceftriaxone** is a third-generation **cephalosporin** and is not the drug of choice for managing diphtheria carriage or prophylaxis. - Its spectrum of activity differs, and it is not recommended for this specific purpose.
Question 1608: Which of the following drugs is ineffective in treating infections caused by Bacteroides fragilis?
- A. Vancomycin
- B. Amikacin (Correct Answer)
- C. Erythromycin
- D. Metronidazole
Explanation: ***Amikacin*** - **Aminoglycosides** like amikacin are **completely ineffective** against *Bacteroides fragilis* due to their oxygen-dependent uptake mechanism. - As an **obligate anaerobe**, *Bacteroides fragilis* lacks the necessary oxygen metabolism to facilitate aminoglycoside entry into bacterial cells. - This represents a **class-wide limitation** of aminoglycosides against all anaerobic bacteria, making this the most definitive answer. *Metronidazole* - **Metronidazole** is the **first-line agent** for treating *Bacteroides fragilis* infections. - It works by forming **toxic free radicals** within anaerobic bacterial cells, causing DNA damage and cell death. - Highly effective with excellent anaerobic coverage. *Erythromycin* - **Erythromycin** and most macrolides have **poor to no activity** against *Bacteroides fragilis*, with most strains showing resistance. - While technically ineffective, it is not the classic teaching example for anaerobic resistance. - Other macrolides like azithromycin similarly lack reliable *B. fragilis* coverage. *Vancomycin* - **Vancomycin** is effective only against **Gram-positive bacteria** and has no activity against Gram-negative anaerobes like *Bacteroides fragilis*. - While also ineffective, it is primarily known for its Gram-positive spectrum limitation rather than anaerobic resistance specifically.
Question 1609: Which of the following statements about cephalosporins is false?
- A. Cefoperazone has got antipseudomonal effect.
- B. Cephalosporins act by inhibiting cell wall synthesis.
- C. Ceftazidime is a 3rd generation cephalosporin.
- D. Cefoxitin has no activity against anaerobes. (Correct Answer)
Explanation: ***Cefoxitin has no activity against anaerobes.*** - This statement is **false** because **cefoxitin** is a second-generation cephalosporin known for its **excellent activity against anaerobic bacteria**, particularly *Bacteroides fragilis*. - Its anaerobic coverage makes it useful for treating infections where these organisms are suspected, such as intra-abdominal and pelvic infections. *Ceftazidime is a 3rd generation cephalosporin.* - This statement is **true**. **Ceftazidime** is a third-generation cephalosporin characterized by its broad-spectrum activity, including significant coverage against **Pseudomonas aeruginosa**. - Its primary clinical utility is often in treating difficult Gram-negative infections. *Cefoperazone has got antipseudomonal effect.* - This statement is **true**. **Cefoperazone** is a third-generation cephalosporin that exhibits **antipseudomonal activity**, similar to ceftazidime. - It is often used for treating infections caused by **Pseudomonas aeruginosa** and other difficult Gram-negative bacteria. *Cephalosporins act by inhibiting cell wall synthesis.* - This statement is **true**. Like other beta-lactam antibiotics, **cephalosporins** exert their bactericidal effect by **inhibiting bacterial cell wall synthesis**. - They bind to and inactivate **penicillin-binding proteins (PBPs)**, which are essential enzymes involved in peptidoglycan cross-linking, leading to compromised cell wall integrity and bacterial lysis.
Question 1610: Which of the following drugs is an antipseudomonal penicillin?
- A. Amoxicillin
- B. Dicloxacillin
- C. Piperacillin (Correct Answer)
- D. Cloxacillin
Explanation: ***Piperacillin*** - **Piperacillin** is a broad-spectrum **antipseudomonal penicillin** (ureidopenicillin) that has significant activity against **Pseudomonas aeruginosa** due to modifications in its side chains. - It works by inhibiting bacterial cell wall synthesis and is often combined with a beta-lactamase inhibitor like **tazobactam** to broaden its spectrum further and overcome resistance. *Amoxicillin* - **Amoxicillin** is an **aminopenicillin** with a broader spectrum than natural penicillins, covering many gram-positive and gram-negative bacteria. - However, it **lacks antipseudomonal activity** and is not effective against **Pseudomonas aeruginosa**. - It does not have the structural modifications required for activity against Pseudomonas species. *Dicloxacillin* - **Dicloxacillin** is an **anti-staphylococcal penicillin** (penicillinase-resistant penicillin) primarily used for infections caused by methicillin-susceptible *Staphylococcus aureus*. - It does not have significant activity against **Pseudomonas aeruginosa** or other gram-negative organisms. *Cloxacillin* - **Cloxacillin** is similar to dicloxacillin, belonging to the **penicillinase-resistant penicillins**, and is used to treat infections caused by *Staphylococcus aureus*. - It lacks the necessary structural modifications to be effective against **Pseudomonas aeruginosa**.
Practice by Chapter
Beta-Lactam Antibiotics
Practice Questions
Aminoglycosides
Practice Questions
Macrolides and Ketolides
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Tetracyclines
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Quinolones
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Sulfonamides and Trimethoprim
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Antimycobacterial Drugs
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Antifungal Agents
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Antiviral Drugs
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Antiparasitic Agents
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Principles of Antimicrobial Selection
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Antimicrobial Resistance
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