Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1341: Which strain is used in the Mumps vaccine?

A. Oka
B. Danish 1331
C. Edmonston Zagreb
D. Jeryl Lynn (Correct Answer)

Explanation: **Jeryl Lynn** - The **Jeryl Lynn strain** is a live attenuated mumps virus strain commonly used in the development of the **mumps vaccine**, particularly in the **MMR vaccine**. - This strain was developed in the 1960s and has a proven track record of safety and efficacy in preventing mumps infection. *Oka* - The **Oka strain** is primarily associated with the **live attenuated varicella (chickenpox) vaccine**. - It is not used in the mumps vaccine, which targets a different viral pathogen. *Danish 1331* - Danish 1331 is a strain associated with a particular **Mycobacterium bovis Bacillus Calmette-Guérin (BCG)** vaccine for **tuberculosis**, not mumps. - BCG vaccines are used to prevent tuberculosis and are distinct from viral vaccines. *Edmonston Zagreb* - The **Edmonston-Zagreb strain** is a live attenuated measles vaccine strain, commonly used in some regions for the **measles, mumps, and rubella (MMR) vaccine**. - While it is part of the MMR vaccine, it specifically targets measles, not mumps.

Question 1342: CDC recommended treatment for uncomplicated gonorrhea -

A. Azithromycin
B. Tetracycline
C. Cotrimoxazole
D. Ceftriaxone (Correct Answer)

Explanation: ***Ceftriaxone*** - As per CDC guidelines, **ceftriaxone** is the recommended treatment for uncomplicated **gonorrhea** due to increasing resistance to other antibiotics. - It is administered as a **single intramuscular dose (500 mg IM)** and is now recommended as monotherapy for uncomplicated gonorrhea. - Additional antibiotic therapy (such as doxycycline or azithromycin) should be added only if **Chlamydia trachomatis** co-infection is suspected or confirmed. *Azithromycin* - While previously used in combination for gonorrhea, **CDC no longer recommends azithromycin as monotherapy** due to increasing rates of resistance. - It may still be used as adjunctive therapy when concurrent **Chlamydia trachomatis** infection is suspected or confirmed, but is not the primary treatment for gonorrhea. *Tetracycline* - **Tetracyclines** are not recommended for the treatment of uncomplicated gonorrhea due to widespread **resistance** and less effective outcomes compared to current recommendations. - **Doxycycline**, a tetracycline derivative, is effective against **Chlamydia trachomatis** but not used as first-line for gonorrhea. *Cotrimoxazole* - **Cotrimoxazole (trimethoprim/sulfamethoxazole)** is not an effective treatment for uncomplicated gonorrhea due to high rates of **resistance** by Neisseria gonorrhoeae. - Its usage is primarily for other bacterial infections, particularly UTIs and certain respiratory infections, and it does not feature in current gonorrhea treatment guidelines.

Question 1343: An appropriate single antibiotic for the empiric treatment of presumed bacterial meningitis in a six month old child would be:

A. Cefotaxime (Correct Answer)
B. Ampicillin
C. Cefadroxil
D. Cefuroxime

Explanation: ***Cefotaxime*** - As a **third-generation cephalosporin**, cefotaxime has excellent penetration into the **cerebrospinal fluid (CSF)** and provides broad-spectrum coverage against common bacterial meningitis pathogens in young children, including *Streptococcus pneumoniae*, *Neisseria meningitidis*, and *Haemophilus influenzae*. - In a 6-month-old child, cefotaxime is an excellent choice for empiric therapy. While both cefotaxime and ceftriaxone are appropriate at this age, cefotaxime is specifically preferred over ceftriaxone in **neonates younger than 28 days** due to concerns about biliary pseudolithiasis and bilirubin displacement, which can worsen jaundice and increase the risk of kernicterus. *Ampicillin* - While effective against *Listeria monocytogenes* (particularly important in neonates and infants <3 months) and Group B *Streptococcus*, ampicillin provides **insufficient coverage** for many other common causes of bacterial meningitis in this age group, particularly penicillin-resistant *Streptococcus pneumoniae* and *Haemophilus influenzae*. - Its use alone as empiric therapy for bacterial meningitis in a 6-month-old would be inadequate, often warranting combination therapy with a third-generation cephalosporin in younger infants. *Cefadroxil* - Cefadroxil is a **first-generation cephalosporin** primarily used for skin, soft tissue, and urinary tract infections. - It has **poor penetration into the CSF** and therefore is not an appropriate choice for treating meningitis. *Cefuroxime* - Cefuroxime is a **second-generation cephalosporin** with limited activity against *Streptococcus pneumoniae* and certain **Gram-negative bacteria** compared to third-generation cephalosporins. - While it has some central nervous system penetration, its efficacy is **inferior to third-generation cephalosporins** like cefotaxime or ceftriaxone for treating bacterial meningitis, especially considering the potential for resistant strains.

Question 1344: 'Savlon' contains:

A. Cetavlon and hibitane (Correct Answer)
B. Hibitane and chloroxylenol
C. Cetavlon and chloroxylenol
D. Chlorhexidine and chloroxylenol

Explanation: ***Cetavlon and hibitane*** - Savlon is a well-known **antiseptic formulation** that contains both **cetrimide** (often marketed as Cetavlon) and **chlorhexidine gluconate** (referred to as hibitane) [1]. - **Cetrimide** is a quaternary ammonium compound acting as a **surfactant** and antiseptic [2], while **chlorhexidine** is a broad-spectrum antiseptic [1]. *Hibitane and chloroxylenol* - While **hibitane (chlorhexidine)** is a component of Savlon [1], **chloroxylenol** is not. - **Chloroxylenol** is the active ingredient in Dettol, another common antiseptic. *Cetavlon and chloroxylenol* - **Cetavlon (cetrimide)** is part of Savlon's formulation [2], but **chloroxylenol** is not. - These two active ingredients originate from different popular antiseptic products. *Chlorhexidine and chloroxylenol* - **Chlorhexidine** is a component of Savlon [1], but **chloroxylenol** is not. - This option incorrectly substitutes part of the Dettol formulation for a component of Savlon.

Question 1345: All of the following drugs cause renal failure except?

A. Cefoperazone (Correct Answer)
B. Amphotericin B
C. Gentamicin
D. Cephaloridine

Explanation: ***Cefoperazone*** - **Cefoperazone** is a third-generation cephalosporin that is primarily eliminated by the liver and does not typically cause **nephrotoxicity**. - While all cephalosporins can potentially cause hypersensitivity reactions or interstitial nephritis in rare cases, cefoperazone is not known for direct renal tubular damage. *Amphotericin B* - **Amphotericin B** is a potent antifungal agent that frequently causes dose-dependent **nephrotoxicity** due to direct damage to renal tubular cells. - It can lead to acute kidney injury, electrolyte imbalances (e.g., **hypokalemia**, **hypomagnesemia**), and renal tubular acidosis. *Gentamicin* - **Gentamicin** is an aminoglycoside antibiotic known for its significant **nephrotoxic** potential, particularly with prolonged use or high doses. - It accumulates in renal cortical cells, leading to **proximal tubular necrosis** and acute tubular necrosis. *Cephaloridine* - **Cephaloridine** is a first-generation cephalosporin that was historically removed from the market due to its significant and dose-dependent **nephrotoxicity**. - It caused direct damage to the **renal tubules**, leading to acute kidney injury.

Question 1346: Which of the following drugs are supplied free of cost to the government Hospital by NACO?

A. Zidovudine
B. Zidovudine + Lamivudine + Nevirapine (Correct Answer)
C. Nevirapine + Zidovudine
D. Nevirapine

Explanation: ***Zidovudine + Lamivudine + Nevirapine*** - This combination represents the **first-line antiretroviral therapy (ART)** typically supplied by NACO (National AIDS Control Organization) for the free distribution to government hospitals. - Providing a **triple drug regimen** is crucial for effective viral suppression and preventing drug resistance in HIV-infected individuals [1].*Zidovudine* - While **Zidovudine** is an important antiretroviral drug, it is usually administered as part of a **combination therapy**, not as a single drug for initial treatment due to the risk of resistance. - NACO's strategy focuses on providing regimens for **optimal patient outcomes**, which involves multiple drugs.*Nevirapine + Zidovudine* - Although this is a **combination**, a complete first-line regimen typically includes three drugs from different classes to maximize efficacy and prevent resistance, such as the addition of **Lamivudine**. - A two-drug regimen would be **suboptimal** for initial treatment according to current ART guidelines.*Nevirapine* - **Nevirapine** is an antiretroviral drug, but like Zidovudine, it is part of a **combination therapy**. - Administering it as a single agent would lead to **rapid development of drug resistance**, rendering the treatment ineffective [1].

Question 1347: Mechanism of action of terbinafine?

A. Inhibition of ergosterol synthesis (Correct Answer)
B. Inhibition of microtubule formation
C. Prevents formation of purine
D. Binds to ergosterol

Explanation: ***Inhibition of ergosterol synthesis*** - Terbinafine specifically inhibits **squalene epoxidase**, an enzyme involved in the **biosynthesis of ergosterol**, a crucial component of fungal cell membranes. - This inhibition leads to the accumulation of **squalene**, which is toxic to the fungal cell, and a deficiency of ergosterol, compromising membrane integrity and fungal growth. *Inhibition of microtubule formation* - This mechanism is characteristic of **griseofulvin**, another antifungal agent, which interferes with fungal mitosis by disrupting the assembly of microtubules. - Terbinafine does not target microtubule formation; its action is focused on the fungal cell membrane pathway. *Prevents formation of purine* - This mechanism is associated with drugs like **flucytosine**, which is converted into an active metabolite that interferes with fungal DNA and RNA synthesis by inhibiting purine and pyrimidine synthesis. - Terbinafine's fungicidal action is unrelated to purine metabolism. *Binds to ergosterol* - This mechanism describes **polyene antifungals** such as **amphotericin B** and **nystatin**, which directly bind to ergosterol in the fungal cell membrane, creating pores and leading to leakage of cellular contents. - Terbinafine does not directly bind to ergosterol but rather prevents its synthesis.

Question 1348: Paucibacillary leprosy treatment includes

A. Rifampicin 600 mg once a month for 6 months + Dapsone 100 mg daily for 6 months (Correct Answer)
B. Rifampicin 600 mg daily + Dapsone 100 mg daily for 6 months
C. Rifampicin 600 mg + Dapsone 100 mg + Clofazimine for 12 months
D. Dapsone 100 mg daily + Clofazimine 300 mg daily for 6 months

Explanation: ***Rifampicin 600 mg once a month for 6 months + Dapsone 100 mg daily for 6 months*** - The World Health Organization (WHO) recommends **multi-drug therapy (MDT)** for paucibacillary leprosy, which comprises **Rifampicin 600 mg once monthly** and **Dapsone 100 mg daily** for a total of **6 months**. - This regimen is crucial for effective bacterial eradication and preventing drug resistance in paucibacillary forms of the disease, which have **five or fewer skin lesions**. - The once-monthly Rifampicin dosing is due to its **potent bactericidal activity** and **prolonged post-antibiotic effect**. *Rifampicin 600 mg daily + Dapsone 100 mg daily for 6 months* - While both drugs are part of the paucibacillary regimen, **Rifampicin** is administered **monthly**, not **daily**. - Daily Rifampicin administration is not the WHO standard and could potentially increase the risk of **side effects** and **drug toxicity** without additional therapeutic benefit in paucibacillary leprosy. *Rifampicin 600 mg + Dapsone 100 mg + Clofazimine for 12 months* - The addition of **Clofazimine** is characteristic of the **multibacillary leprosy** regimen, not paucibacillary. - **Multibacillary leprosy** involves extensive disease (more than 5 skin lesions) with higher bacterial load and requires a **12-month treatment** duration with three drugs including Clofazimine. *Dapsone 100 mg daily + Clofazimine 300 mg daily for 6 months* - This regimen excludes **Rifampicin**, which is a critical component of treatment for both paucibacillary and multibacillary leprosy due to its **strong bactericidal action**. - Furthermore, **Clofazimine** is typically included in **multibacillary regimens** and is not part of the standard paucibacillary protocol.

Question 1349: The drug of choice in mycoplasma pneumonia in children is –

A. Tetracycline
B. Cotrimoxazole
C. Streptomycin
D. Erythromycin (Correct Answer)

Explanation: ***Erythromycin*** - **Erythromycin**, a macrolide antibiotic, is the drug of choice for treating **Mycoplasma pneumoniae** infections in children. - **Mycoplasma pneumoniae** lacks a cell wall, making antibiotics that target cell wall synthesis (like penicillins or cephalosporins) ineffective. Macrolides inhibit protein synthesis. *Tetracycline* - **Tetracyclines** are effective against **Mycoplasma pneumoniae**, but are generally avoided in children under 8 years due to the risk of permanent **tooth discoloration** and **bone growth inhibition**. - While effective, its side effect profile in pediatric patients makes it a less preferred first-line option. *Cotrimoxazole* - **Cotrimoxazole** (trimethoprim/sulfamethoxazole) is effective against various bacterial infections but is not the primary drug of choice for **Mycoplasma pneumoniae**. - Its mechanism of action involves inhibiting folate synthesis, which is not the principal target for **Mycoplasma** infections. *Streptomycin* - **Streptomycin** is an aminoglycoside antibiotic primarily used for treating **tuberculosis** and some severe gram-negative infections. - It is not effective against **Mycoplasma pneumoniae** and has significant side effects, including **ototoxicity** and **nephrotoxicity**.

Question 1350: Which one of the following antibiotics inhibits transpeptidation in bacterial cell wall synthesis?

A. Penicillin (Correct Answer)
B. Chloramphenicol
C. Amphotericin
D. Vancomycin

Explanation: ***Penicillin*** - Penicillin is a **beta-lactam antibiotic** that targets bacterial cell wall synthesis by inhibiting the enzyme **transpeptidase** (penicillin-binding proteins). - This inhibition prevents the cross-linking of **peptidoglycan strands**, leading to a weakened cell wall and subsequent bacterial lysis. *Chloramphenicol* - **Chloramphenicol** inhibits bacterial protein synthesis by binding to the **50S ribosomal subunit**, thereby preventing peptide bond formation (peptidyl transferase activity). - It does not act on the bacterial cell wall. *Vancomycin* - **Vancomycin** is a **glycopeptide antibiotic** that inhibits bacterial cell wall synthesis by binding to the **D-Ala-D-Ala terminus** of peptidoglycan precursors. - It prevents the **transglycosylation and transpeptidation steps** by blocking substrate access, but it does not directly inhibit the transpeptidase enzyme itself like beta-lactams do. - Its mechanism is distinct from penicillin's direct enzyme inhibition. *Amphotericin* - **Amphotericin B** is an **antifungal agent** that targets the fungal cell membrane by binding to **ergosterol**, forming pores that disrupt membrane integrity. - It has no activity against bacterial cell wall synthesis.

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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