Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1621: Which of the following drugs controls lepra reactions in leprosy?

A. Dapsone
B. Streptomycin
C. Ethambutol
D. Clofazimine (Correct Answer)

Explanation: ***Clofazimine*** - **Clofazimine** is an anti-leprosy drug known for its **anti-inflammatory** and **immunomodulatory properties**, which help control **lepromin reactions** (specifically ENL or Type 2 lepra reactions) [1, 2]. - It stabilizes **mast cell membranes** and inhibits lymphocyte proliferation, thereby reducing the inflammatory response seen in lepromin reactions. *Dapsone* - **Dapsone** is a primary anti-leprosy drug that works by inhibiting **folate synthesis** in *Mycobacterium leprae* [2]. - While effective against the bacteria, it does not directly control the **immunological reactions** associated with leprosy, such as the lepromin reaction [1]. *Streptomycin* - **Streptomycin** is an antibiotic primarily used for **tuberculosis** and other bacterial infections, belonging to the **aminoglycoside** class. - It is **not a first-line drug** for leprosy and has no established role in controlling lepromin reactions. *Ethambutol* - **Ethambutol** is an anti-tuberculosis drug that inhibits **mycolic acid synthesis**, leading to impaired cell wall formation in mycobacteria. - It is **not used for treating leprosy** and therefore has no function in managing lepromin reactions.

Question 1622: Which species of Plasmodium is known for its common resistance to chloroquine?

A. Plasmodium falciparum (Correct Answer)
B. Plasmodium vivax
C. Plasmodium malariae
D. Plasmodium ovale

Explanation: ***Plasmodium falciparum*** - **Plasmodium falciparum** is the species most commonly associated with severe malaria and has widespread resistance to **chloroquine**, primarily due to mutations in the **PfCRT** (_P. falciparum_ chloroquine resistance transporter) gene - Due to its high morbidity and mortality and the prevalence of **chloroquine resistance**, it often necessitates treatment with **artemisinin-based combination therapies (ACTs)** - Resistance is particularly widespread in sub-Saharan Africa, Southeast Asia, and South America *Plasmodium vivax* - While **P. vivax** resistance to chloroquine is emerging in some regions (Papua New Guinea, Indonesia), it is not as widespread or well-established globally as it is with **P. falciparum** - **P. vivax** is known for forming **hypnozoites** in the liver, requiring primaquine to prevent relapses, a feature not directly related to chloroquine resistance *Plasmodium malariae* - **P. malariae** primarily causes a milder form of malaria and remains largely susceptible to **chloroquine** - It is known for its relatively long incubation period and potential to cause **nephrotic syndrome** *Plasmodium ovale* - **P. ovale** is rare and generally confined to specific regions in West Africa, and like **P. malariae**, it remains largely susceptible to **chloroquine** - Similar to **P. vivax**, it forms **hypnozoites** in the liver, which can lead to relapses if not treated with primaquine

Question 1623: The drug that should be used for prophylaxis of close contacts of a patient suffering from meningococcal meningitis is:

A. Rifampicin (Correct Answer)
B. Amikacin
C. Erythromycin
D. Dapsone

Explanation: ***Rifampicin*** - **Rifampicin** is a primary agent for meningococcal prophylaxis due to its ability to eliminate carriage of *Neisseria meningitidis* from the nasopharynx. - It is effective, given orally, and reaches high concentrations in respiratory secretions. *Erythromycin* - While **erythromycin** is an antibiotic, it is not the preferred drug for **meningococcal prophylaxis** because it is less effective at eradicating nasopharyngeal carriage of *N. meningitidis* compared to rifampicin. - It also has a broader spectrum and higher potential for gastrointestinal side effects when used for prophylaxis. *Amikacin* - **Amikacin** is an aminoglycoside antibiotic primarily used for severe Gram-negative bacterial infections and is typically administered intravenously. - It is not effective for meningococcal prophylaxis as it does not adequately penetrate the nasopharynx and is not active against **meningococci** in this context. *Dapsone* - **Dapsone** is an antibacterial drug primarily used for the treatment of leprosy and dermatitis herpetiformis, as well as *Pneumocystis jirovecii* pneumonia prophylaxis in immunocompromised individuals. - It has no role in the prophylaxis or treatment of **meningococcal meningitis**.

Question 1624: Which of the following is not a component of the influenza trivalent vaccine?

A. H1N1 virus
B. Influenza B virus
C. H3N2 virus
D. H5N1 virus (Correct Answer)

Explanation: ***H5N1 virus*** - The **H5N1 virus** is not a standard component of seasonal influenza trivalent vaccines because it is primarily an **avian influenza** strain, rarely infecting humans. - While it can cause severe disease in humans, it has not achieved sustained human-to-human transmission, unlike the circulating seasonal influenza strains. *H1N1 virus* - The **H1N1 virus** is a common component of seasonal influenza vaccines, including trivalent ones, as it is a prevalent **influenza A** strain responsible for human infections worldwide. - It was notably associated with the **2009 influenza pandemic** and continues to circulate annually. *Influenza B virus* - **Influenza B virus** is a standard component of both trivalent and quadrivalent influenza vaccines, as it causes significant seasonal illness in humans. - Trivalent vaccines typically include one lineage of **influenza B** (either Victoria or Yamagata), while quadrivalent vaccines include both. *H3N2 virus* - The **H3N2 virus** is another common and important component of seasonal influenza vaccines, including trivalent ones, as it is a prevalent **influenza A** strain. - It is often associated with more severe disease and hospitalizations, particularly in older adults and young children.

Question 1625: Which of the following drugs used in anti-tubercular therapy is a potent bactericidal agent that inhibits RNA synthesis?

A. Pyrazinamide
B. Ethambutol
C. PAS
D. Rifampicin (Correct Answer)

Explanation: ***Rifampicin*** - **Rifampicin** is a potent **bactericidal** anti-tubercular drug that inhibits bacterial **RNA synthesis** by binding to DNA-dependent RNA polymerase. - It is effective against both **rapidly dividing** and **metabolically active** *M. tuberculosis* strains. - Among first-line anti-TB drugs, it is considered the most potent bactericidal agent with sterilizing activity. *Pyrazinamide* - **Pyrazinamide** is **bactericidal** against **intracellular** and **slowly replicating** *M. tuberculosis* in acidic environments. - Its mechanism involves disrupting **mycobacterial membrane metabolism** and **transport functions** under acidic conditions, not RNA synthesis. - It has unique sterilizing activity against dormant bacilli. *Ethambutol* - **Ethambutol** is primarily **bacteriostatic**, inhibiting the synthesis of the **mycobacterial cell wall** by interfering with arabinosyl transferases. - It prevents the formation of **arabinogalactan**, an essential component of the mycobacterial cell wall. *PAS* - **Para-aminosalicylic acid (PAS)** is a **bacteriostatic** drug that inhibits **folic acid synthesis** in *M. tuberculosis*, similar to sulfonamides. - It is a **second-line agent** used primarily in cases of drug resistance.

Question 1626: What is the first-line treatment for syphilis?

A. Penicillin G (Correct Answer)
B. Tetracycline
C. Erythromycin
D. Rifampicin

Explanation: ***Penicillin G*** - **Penicillin G** is the **drug of choice** for all stages of syphilis due to its high efficacy against *Treponema pallidum*. - Its long duration of action, particularly **benzathine penicillin G**, provides sustained treponemicidal levels for early syphilis and prevents neurosyphilis progression. *Rifampicin* - **Rifampicin** is primarily used in the treatment of **tuberculosis** and other mycobacterial infections. - It has no significant role in the treatment of syphilis and is not effective against *Treponema pallidum*. *Tetracycline* - **Tetracycline** can be used as an **alternative treatment** for syphilis in patients with penicillin allergy. - However, it is not considered first-line due to potential side effects and the need for longer treatment courses compared to penicillin. *Erythromycin* - **Erythromycin** is an older macrolide antibiotic that can be used as an **alternative treatment for early syphilis** in penicillin-allergic pregnant patients. - Its efficacy is less reliable than penicillin G, and it is not recommended for later stages of syphilis or in non-pregnant individuals due to increasing resistance.

Question 1627: Which class of antiretroviral drug does Nevirapine belong to?

A. NRTI
B. NNRTI (Correct Answer)
C. INSTI
D. PI

Explanation: ***NNRTI*** - **Nevirapine** is a first-generation non-nucleoside reverse transcriptase inhibitor (NNRTI) used in the treatment of HIV-1 infection. - **NNRTIs** bind directly to the reverse transcriptase enzyme at a site distinct from the active site, causing a conformational change that inactivates the enzyme and prevents viral DNA synthesis. - Other examples include **efavirenz, etravirine, and rilpivirine**. *NRTI* - **NRTIs** (nucleoside/nucleotide reverse transcriptase inhibitors) are prodrugs that require intracellular phosphorylation to active triphosphate forms. - They act as competitive inhibitors of reverse transcriptase and cause chain termination when incorporated into viral DNA. - Examples include **zidovudine, lamivudine, tenofovir, and emtricitabine**. *PI* - **PIs** (Protease Inhibitors) block the HIV protease enzyme, preventing cleavage of viral polyproteins into functional proteins. - This results in the production of immature, non-infectious viral particles. - Examples include **ritonavir, atazanavir, darunavir, and lopinavir**. *INSTI* - **INSTIs** (Integrase Strand Transfer Inhibitors) block the HIV integrase enzyme, preventing integration of viral DNA into the host chromosome. - This prevents establishment of permanent infection in the host cell. - Examples include **raltegravir, dolutegravir, and bictegravir**.

Question 1628: Sudha, a 20-year-old female, developed antibiotic-associated pseudomembranous colitis caused by Clostridium difficile. Among the following drugs, which is most likely to be effective in the treatment of this disease?

A. Metronidazole (Correct Answer)
B. Ampicillin
C. Clindamycin
D. Chloramphenicol

Explanation: ***Metronidazole*** - Among the options listed, **Metronidazole** is the most effective for treating **Clostridioides difficile infection (CDI)**. - It works by disrupting bacterial DNA synthesis and is highly effective against **anaerobic bacteria** like *C. difficile*. - **Note:** Current guidelines (IDSA/SHEA 2021) recommend **oral vancomycin or fidaxomicin as first-line therapy**, with metronidazole reserved for situations where preferred agents are unavailable. However, among the drugs listed here, metronidazole remains the correct choice. *Ampicillin* - **Ampicillin** is a penicillin-class antibiotic and is **ineffective** against *Clostridioides difficile*. - It is one of the antibiotics that can **trigger** antibiotic-associated pseudomembranous colitis by disrupting normal gut flora and promoting *C. difficile* overgrowth. *Clindamycin* - **Clindamycin** is notorious for being a common cause of **antibiotic-associated pseudomembranous colitis** due to *Clostridioides difficile*. - It would **exacerbate** rather than treat the condition, making it an inappropriate choice. *Chloramphenicol* - **Chloramphenicol** is a broad-spectrum antibiotic that is **not effective** for treating *Clostridioides difficile* infection. - Its use is limited due to significant side effects, including **bone marrow suppression** (aplastic anemia), and it is not a recommended treatment for CDI.

Question 1629: Which second-line AKT drug is known to cause peripheral neuropathy?

A. Ethionamide (Correct Answer)
B. Rifabutin
C. PAS
D. Moxifloxacin

Explanation: ***Ethionamide*** - **Ethionamide** is a second-line anti-tuberculosis drug known to cause a variety of dose-dependent adverse effects, including **peripheral neuropathy**. - This side effect is thought to be due to its structural similarity to **isoniazid**, another anti-tuberculosis drug that commonly causes neuropathy through **pyridoxine (vitamin B6) deficiency**. *Rifabutin* - **Rifabutin** is a rifamycin derivative primarily used as a second-line agent for multi-drug resistant tuberculosis and in patients with HIV to prevent *Mycobacterium avium* complex (MAC) infection. - Its main side effects include **gastrointestinal upset**, **rash**, and **neutropenia**, and it is not typically associated with peripheral neuropathy. *PAS (Para-aminosalicylic acid)* - **PAS** is an older second-line anti-tuberculosis drug that primarily causes **gastrointestinal disturbances** such as nausea, vomiting, diarrhea, and abdominal pain. - It can also lead to **hypersensitivity reactions** and **drug-induced hepatitis**, but **peripheral neuropathy** is not a characteristic side effect. *Moxifloxacin* - **Moxifloxacin** is a fluoroquinolone antibiotic used in the treatment of tuberculosis, including multi-drug resistant strains. - Although fluoroquinolones, as a class, can rarely cause peripheral neuropathy, it is not a prominent or distinguishing side effect of moxifloxacin in the context of second-line anti-tuberculosis drugs compared to ethionamide.

Question 1630: Which of the following antibiotics does not contain a beta-lactam ring?

A. Penicillin
B. Linezolid (Correct Answer)
C. Cefotaxime
D. Imipenem

Explanation: ***Linezolid*** - **Linezolid** is an **oxazolidinone antibiotic**, which has a different chemical structure and mechanism of action compared to beta-lactams. - It works by inhibiting bacterial **protein synthesis** at the ribosomal level, specifically binding to the 23S ribosomal RNA of the 50S subunit. *Penicillin* - **Penicillin** is the prototypic **beta-lactam antibiotic**, characterized by a four-membered beta-lactam ring in its chemical structure [1]. - Its mechanism of action involves inhibiting **bacterial cell wall synthesis** by binding to penicillin-binding proteins (PBPs) [3]. *Cefotaxime* - **Cefotaxime** is a **third-generation cephalosporin**, which belongs to the beta-lactam class of antibiotics [1], [2]. - All cephalosporins, like penicillins, possess a **beta-lactam ring** essential for their antibacterial activity [3]. *Imipenem* - **Imipenem** is a **carbapenem antibiotic**, another class within the beta-lactam family [1]. - Like other beta-lactams, it contains a **beta-lactam ring** and acts by interfering with bacterial **cell wall synthesis** [3].

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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