Antimicrobial Agents — MCQs
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What is the drug of choice for treating onychomycosis?
Which of the following statements about vitamin K is correct?
Burkholderia cepacia is resistant to which of the following antibiotics?
Anaerobes are resistant intrinsically against which of the following?
Meningococcal polysaccharide vaccine (MPSV4) contains?
Dose of benzathine penicillin G to be given in patients with latent syphilis without penicillin allergy and normal CSF findings is
Rota-teq oral vaccine for rotavirus contains how many reassorted rotaviruses?
Which of the following is most active against slowly dividing tubercular bacilli ?
Which macrolide is MOST active against Mycobacterium leprae?
Which of the following is a topical antifungal agent?
Antimicrobial Agents Indian Medical PG Practice Questions and MCQs
Question 1481: What is the drug of choice for treating onychomycosis?
- A. Terbinafine (Correct Answer)
- B. Fluconazole
- C. Nystatin
- D. Itraconazole
Explanation: ***Terbinafine*** - **Terbinafine** is the preferred first-line oral antifungal agent for treating **onychomycosis** due to its high efficacy and favorable safety profile. - It accumulates in the nail plate, providing sustained therapeutic levels that result in high cure rates. *Fluconazole* - While effective against some fungal infections, **fluconazole** is typically a second-line choice for onychomycosis, often reserved for patients who cannot tolerate or prefer not to use terbinafine. - It has a broader spectrum but generally shows lower efficacy for dermatophyte-induced onychomycosis compared to terbinafine. *Nystatin* - **Nystatin** is primarily effective against **Candida** species and is rarely effective against the **dermatophytes** that commonly cause onychomycosis. - It is typically used for topical treatment of mucocutaneous candidiasis and is not suitable for systemic or nail plate penetration. *Itraconazole* - **Itraconazole** is an effective oral antifungal for onychomycosis, often used in a pulse-dosing regimen, but it can have more significant drug interactions and a less favorable safety profile than terbinafine. - It is considered an alternative or second-line agent, especially in cases where terbinafine is not tolerated or effective.
Question 1482: Which of the following statements about vitamin K is correct?
- A. All of the options are true
- B. Vitamin K acts as an anticoagulant
- C. Prolonged use of antimicrobials can lead to vitamin K deficiency (Correct Answer)
- D. The recommended dietary allowance for vitamin K is 200-300 micrograms per day
Explanation: ### Prolonged use of antimicrobials can lead to vitamin K deficiency - Long-term use of **broad-spectrum antimicrobials** can reduce the populations of gut bacteria that synthesize **vitamin K**, leading to a deficiency [1]. - This is particularly relevant because a significant portion of the body's vitamin K supply, especially **K2 (menaquinone)**, comes from microbial production in the intestines [1]. ### Vitamin K acts as an anticoagulant - Vitamin K is essential for the synthesis of **coagulation factors II, VII, IX, and X**, as well as protein C and S [3]; therefore, it is a **procoagulant**, not an anticoagulant [2]. - **Anticoagulants** like **warfarin** work by *inhibiting* vitamin K's action, thereby preventing the activation of these clotting factors [2], [3]. ### All of the options are true - This statement is incorrect because, as explained above, vitamin K is a **procoagulant**, not an anticoagulant. - The other statements also contain inaccuracies regarding vitamin K's function and recommended daily allowance. ### The recommended dietary allowance for vitamin K is 200-300 micrograms per day - The recommended daily allowance (RDA) for vitamin K in adults is significantly lower, typically **90 micrograms per day for women** and **120 micrograms per day for men**, not 200-300 micrograms [1]. - Excessive intake of vitamin K is generally not a concern as it has low toxicity due to its limited storage in the body.
Question 1483: Burkholderia cepacia is resistant to which of the following antibiotics?
- A. Cefepime
- B. Piperacillin-tazobactam
- C. Meropenem
- D. Cefotetan (Correct Answer)
Explanation: ***Cefotetan*** - *Burkholderia cepacia* complex is **intrinsically resistant to second-generation cephalosporins** like cefotetan. - This resistance is mediated by **chromosomally encoded AmpC beta-lactamases** and reduced outer membrane permeability. - Second-generation cephalosporins have **no role** in treating *B. cepacia* infections. *Cefepime* - **Cefepime** (fourth-generation cephalosporin) shows **variable activity** against *B. cepacia* complex. - While it has enhanced stability against some beta-lactamases, resistance is common and susceptibility testing is required. - It may be used in some cases but is **not consistently effective**. *Piperacillin-tazobactam* - **Piperacillin-tazobactam** demonstrates **variable and often limited activity** against *B. cepacia* complex. - Susceptibility is strain-dependent and must be confirmed by testing before use. - The tazobactam component does not adequately inhibit the chromosomal beta-lactamases of *B. cepacia*. *Meropenem* - **Meropenem** and other carbapenems show **better but still variable activity** against *B. cepacia* complex. - While historically considered a treatment option, **carbapenem resistance is increasingly common**. - Treatment should be guided by susceptibility testing; ceftazidime, meropenem, and minocycline are among the agents with better (though inconsistent) activity.
Question 1484: Anaerobes are resistant intrinsically against which of the following?
- A. Aminoglycosides (Correct Answer)
- B. Azithromycin
- C. Metronidazole
- D. Beta lactam antibiotics
Explanation: ***Aminoglycosides*** - **Aminoglycosides** require an **oxygen-dependent transport system** to enter bacterial cells. [3] - Since **anaerobes** thrive in low-oxygen environments, this transport system is inactive, making them intrinsically resistant to aminoglycosides. [3] *Azithromycin* - **Azithromycin** (a macrolide) inhibits protein synthesis by binding to the 50S ribosomal subunit. - Many anaerobes are susceptible to **azithromycin**, making it an effective treatment for certain anaerobic infections. *Metronidazole* - **Metronidazole** is a potent prodrug that requires reduction by **anaerobic metabolism** to become active. [1], [2] - Its mechanism of action involves creating **cytotoxic free radicals** that damage DNA, making it highly effective against most anaerobes. [2] *Beta lactam antibiotics* - **Beta-lactam antibiotics**, such as **penicillins** and **cephalosporins**, interfere with bacterial cell wall synthesis. - While some anaerobes are susceptible, others have developed resistance mechanisms like producing **beta-lactamase enzymes**, but they are not intrinsically resistant across the board. [4]
Question 1485: Meningococcal polysaccharide vaccine (MPSV4) contains?
- A. 50 mcg of polysaccharide of each strain (Correct Answer)
- B. 100 mcg of polysaccharide of each strain
- C. 1000 mcg of polysaccharide of each strain
- D. 5000 mcg of polysaccharide of each strain
Explanation: ***50 mcg of polysaccharide of each strain*** - The **polysaccharide meningococcal vaccine (MPSV4)** contains **50 mcg** of purified capsular polysaccharide from each of the four serogroups (A, C, W-135, and Y). - This specific dosage ensures an adequate immune response without causing excessive reactogenicity. *100 mcg of polysaccharide of each strain* - This dosage is **higher** than the standard concentration found in MPSV4 and is not the correct amount per strain. - Using a higher concentration could potentially increase adverse reactions without significantly enhancing immunogenicity. *1000 mcg of polysaccharide of each strain* - This amount is **significantly higher** than the immunologically effective dose for meningococcal polysaccharides. - Such a high dose would be economically unfeasible and likely lead to higher rates of side effects. *5000 mcg of polysaccharide of each strain* - This is an **extremely high** and impractical dosage for a vaccine. - It would be associated with a high risk of adverse events and would not be used in vaccine formulations.
Question 1486: Dose of benzathine penicillin G to be given in patients with latent syphilis without penicillin allergy and normal CSF findings is
- A. 1.8 million units (mU) IM / week for 3 weeks
- B. 2.4 million units (mU) IM / week for 3 weeks (Correct Answer)
- C. 2.0 million units (mU) IM / week for 3 weeks
- D. 3.0 million units (mU) IM / week for 3 weeks
Explanation: ***2.4 million units (mU) IM / week for 3 weeks*** - This is the **standard CDC-recommended regimen** for treating **latent syphilis** in patients without penicillin allergy and normal CSF findings. - The extended duration and specific dosage ensure adequate drug levels to eradicate the infection in its latent phase. *1.8 million units (mU) IM / week for 3 weeks* - This dose is **insufficient** for the treatment of latent syphilis. - Subtherapeutic dosing can lead to treatment failure and progression of the disease. *2.0 million units (mU) IM / week for 3 weeks* - While closer to the correct dose, 2.0 mU is **not the recommended standard** for latent syphilis. - Adherence to established guidelines is crucial for effective treatment of syphilis. *3.0 million units (mU) IM / week for 3 weeks* - This dosage is **higher than necessary** for latent syphilis and could potentially increase the risk of side effects, although usually not severe with single dose. - Overdosing does not offer additional therapeutic benefit for latent syphilis compared to the standard regimen.
Question 1487: Rota-teq oral vaccine for rotavirus contains how many reassorted rotaviruses?
- A. 3 reassorted rotaviruses
- B. 4 reassorted rotaviruses
- C. 2 reassorted rotaviruses
- D. 5 reassorted rotaviruses (Correct Answer)
Explanation: ***5 reassorted rotaviruses*** - **RotaTeq** (RV5) is a pentavalent vaccine containing **five live attenuated human-bovine reassortant rotaviruses**. - These reassortants express four different G serotypes (G1, G2, G3, G4) and one P serotype (P1A[8]), providing broad protection against common rotavirus strains causing severe gastroenteritis. *2 reassorted rotaviruses* - This option is incorrect as **RotaTeq** contains five reassorted rotaviruses, not two. - The number two is not associated with any of the currently available rotavirus vaccines. *3 reassorted rotaviruses* - This option is incorrect. **RotaTeq** does not contain three reassorted rotaviruses. - No major rotavirus vaccine contains exactly three reassorted strains. *4 reassorted rotaviruses* - This option is incorrect. **RotaTeq** specifically contains five reassorted rotaviruses, not four. - While other rotavirus vaccines exist (e.g., Rotarix is monovalent), none are based on four reassorted strains.
Question 1488: Which of the following is most active against slowly dividing tubercular bacilli ?
- A. Isoniazid
- B. Rifampicin (Correct Answer)
- C. Streptomycin
- D. Ethambutol
Explanation: ***Rifampicin*** - **Rifampicin** is highly effective against both rapidly and **slowly metabolizing** populations of *Mycobacterium tuberculosis*, including **persister bacilli** within macrophages and caseous lesions. - Its ability to penetrate host cells and kill semi-dormant organisms makes it crucial for shortening treatment duration and preventing relapse. - Among the given options, it has the **best sterilizing activity** against slow-growing tubercular populations. *Isoniazid* - **Isoniazid (INH)** is primarily bactericidal against **rapidly dividing** *Mycobacterium tuberculosis* but has limited activity against slowly dividing or dormant bacilli. - It targets mycolic acid synthesis, which is essential for rapidly growing cells but less critical for metabolically inactive cells. *Streptomycin* - **Streptomycin** primarily targets **rapidly multiplying** extracellular bacilli and has poor activity against intracellular or slowly dividing organisms. - Its action is dependent on active protein synthesis, which is significantly reduced in dormant states. *Ethambutol* - **Ethambutol** is mainly **bacteriostatic** and active against multiplying bacilli, preventing mycobacterial cell wall formation. - It is less effective against dormant or slowly replicating bacteria within caseous lesions.
Question 1489: Which macrolide is MOST active against Mycobacterium leprae?
- A. Erythromycin
- B. Azithromycin
- C. Roxithromycin
- D. Clarithromycin (Correct Answer)
Explanation: **Correct: Clarithromycin** - **Clarithromycin** is the most active macrolide against **Mycobacterium leprae**, with significant in-vitro and in-vivo bactericidal activity - It is a preferred macrolide for leprosy treatment, particularly useful as an alternative in multidrug therapy (MDT) regimens - Its efficacy is attributed to its ability to attain **high intracellular concentrations** and effectively inhibit mycobacterial protein synthesis - Superior to other macrolides in terms of potency against *M. leprae* *Incorrect: Azithromycin* - While **azithromycin** possesses some activity against *M. leprae*, its potency is **less than clarithromycin** - It has a longer half-life and good tissue penetration, but is not the most active macrolide for this indication - Sometimes used in leprosy regimens, but not typically cited as the most active macrolide *Incorrect: Roxithromycin* - **Roxithromycin** has demonstrated some activity against *M. leprae* in laboratory settings, but is **not as extensively studied or commonly used** as clarithromycin for leprosy - Its clinical utility for leprosy is less well-established - Not considered first-line among macrolides for this indication *Incorrect: Erythromycin* - **Erythromycin**, the first macrolide discovered, has **limited activity** against *M. leprae* compared to newer macrolides like clarithromycin - Poor bioavailability and more frequent dosing requirements make it less practical - Not considered a primary agent for the treatment of leprosy
Question 1490: Which of the following is a topical antifungal agent?
- A. Benzyl benzoate
- B. Brimetenide
- C. Butenafine (Correct Answer)
- D. Posaconazole
Explanation: ***Butenafine*** - **Butenafine** belongs to the class of **benzylamine antifungals** and is used topically to treat fungal infections such as **tinea pedis (athlete's foot)**, **tinea cruris (jock itch)**, and **tinea corporis (ringworm)**. - Its mechanism of action involves inhibiting **squalene epoxidase**, an enzyme essential for fungal cell membrane synthesis, leading to **ergosterol depletion** and accumulation of squalene, which is toxic to the fungus. *Benzyl benzoate* - **Benzyl benzoate** is primarily used as a **topical scabicide** and **pediculicide**, meaning it targets mites (scabies) and lice. - It works by acting as a **neurotoxin** to these parasites, causing paralysis and death, and is not classified as an antifungal agent. *Brimetenide* - This option appears to be a **misspelling** or **non-existent drug name** in common pharmaceutical contexts. - There is no widely recognized drug with the name **"Brimetenide"** that serves as an antifungal. *Posaconazole* - **Posaconazole** is a **systemic triazole antifungal**, typically administered orally or intravenously for the treatment and prophylaxis of invasive fungal infections in immunocompromised patients. - While it is an antifungal, its primary use is **systemic** rather than topical for treating superficial dermatophyte infections.
Practice by Chapter
Beta-Lactam Antibiotics
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Aminoglycosides
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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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