Antimicrobial Agents — MCQs
On this page
What is the drug of choice for treating onychomycosis?
Anaerobes are resistant intrinsically against which of the following?
Burkholderia cepacia is resistant to which of the following antibiotics?
Which of the following statements about vitamin K is correct?
Which of the following is most active against slowly dividing tubercular bacilli ?
Rota-teq oral vaccine for rotavirus contains how many reassorted rotaviruses?
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
Which of the following is a topical antifungal agent?
Which of the following statements about the primary clinical use of levamisole is true?
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: 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 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: 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 1485: 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 1486: 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 1487: 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 1488: 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 1489: 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.
Question 1490: Which of the following statements about the primary clinical use of levamisole is true?
- A. It has immunomodulator action
- B. It is the levoisomer of tetramisole
- C. It can kill strongyloides larvae and adult worms
- D. It is used against ascariasis and ancyclostomiasis (Correct Answer)
Explanation: ***It is used against ascariasis and ancyclostomiasis*** - **Levamisole** is an **anthelmintic drug** primarily used for the treatment of **nematode infections**, specifically **roundworms (Ascaris lumbricoides)** and **hookworms (Ancylostoma duodenale)**. - It works by **paralyzing the worms**, leading to their expulsion in the feces. *It is the levoisomer of tetramisole* - While it is true that **levamisole** is the **levorotatory isomer** of **tetramisole**, this statement describes its chemical structure, not its primary clinical use. - **Tetramisole** itself exists as a **racemic mixture** of both levo and dextro isomers. *It has immunomodulator action* - **Levamisole** does possess **immunomodulatory properties** at lower doses and was historically investigated for conditions like **rheumatoid arthritis** and as an adjuvant in colon cancer. - However, its primary and most widespread clinical use is as an **anthelmintic**, not as an immunomodulator, especially due to concerns about side effects like **agranulocytosis**. *It can kill strongyloides larvae and adult worms* - **Levamisole** is **not effective** against **Strongyloides stercoralis** (threadworms). - The drug of choice for **strongyloidiasis** is typically **ivermectin** or **albendazole**.
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
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free