Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1411: Antibiotic treatment of choice for treating cholera in an adult is a single dose of:

A. Co-trimoxazole
B. Doxycycline (Correct Answer)
C. Furazolidone
D. Tetracycline

Explanation: ***Doxycycline***- **Doxycycline** is the recommended first-line antibiotic for cholera in adults due to its effectiveness in reducing stool volume and duration of diarrhea, and it is often given as a **single oral dose**.- Its broad-spectrum activity and good oral bioavailability make it a practical choice for treating **Vibrio cholerae** infections, especially in outbreak settings.*Co-trimoxazole*- While **co-trimoxazole (trimethoprim-sulfamethoxazole)** can be effective against some strains of Vibrio cholerae, resistance has become more common, limiting its use as a first-line agent.- Its efficacy as a single-dose treatment for cholera is generally less established compared to doxycycline.*Furazolidone*- **Furazolidone** has been used in the past for cholera treatment, but its use has declined due to concerns about side effects and the development of resistance.- It is not typically recommended as the first-line treatment for cholera in adults, particularly as a single dose.*Tetracycline*- **Tetracycline** is historically effective against cholera, but modern guidelines often prefer doxycycline due to its improved tolerability, once-daily dosing, and similar efficacy profile.- The older tetracyclines often require multiple doses per day, which can impact patient compliance compared to a single-dose regimen of doxycycline.

Question 1412: A 14-year-old boy presents with headache, fever, and cough for 2 days. Sputum is scant and non-purulent and gram stain reveals many white cells but no organisms. The treatment should be initiated with :

A. Azithromycin (Correct Answer)
B. Levofloxacin
C. Amikacin
D. Cefazolin

Explanation: ***Azithromycin*** - The clinical picture of **headache, fever, cough, scant non-purulent sputum**, and Gram stain showing white cells but no organisms is highly suggestive of **atypical pneumonia**, likely caused by *Mycoplasma pneumoniae* in this age group. - **Macrolides** like azithromycin are the **first-line treatment** for atypical pneumonia as they are effective against organisms like *Mycoplasma* and *Chlamydia* which lack cell walls and are therefore resistant to beta-lactam antibiotics. *Levofloxacin* - **Levofloxacin** is a **fluoroquinolone**, which is effective against atypical pathogens but is generally reserved for **older patients** or those with **allergies** to macrolides due to concerns about potential side effects like cartilage damage in children. - Using fluoroquinolones as a first-line treatment in adolescents for suspected atypical pneumonia is **not recommended** due to these potential side effects and the availability of safer alternatives. *Amikacin* - **Amikacin** is an **aminoglycoside antibiotic** primarily used for severe infections caused by **Gram-negative bacteria**. - It is **ineffective against atypical bacteria** like *Mycoplasma* or *Chlamydia* which are the likely causative agents in this scenario. *Cefazolin* - **Cefazolin** is a **first-generation cephalosporin**, which is a **beta-lactam antibiotic** effective mostly against Gram-positive cocci and some Gram-negative bacteria. - It is **ineffective against atypical pathogens** because these organisms **lack a cell wall** (like *Mycoplasma*) or have cell walls that are not targeted by beta-lactam antibiotics.

Question 1413: A fungicidal drug that can be used orally for the treatment of onychomycosis is :

A. Griseofulvin
B. Terbinafine (Correct Answer)
C. Amphotericin B
D. Clotrimazole

Explanation: ***Terbinafine*** - **Terbinafine** is a highly effective **fungicidal** agent prescribed orally for **onychomycosis** due to its ability to concentrate in the nail bed. - It works by inhibiting **squalene epoxidase**, an enzyme essential for fungal ergosterol synthesis, leading to fungal cell death. *Griseofulvin* - **Griseofulvin** is a **fungistatic** drug that inhibits fungal cell division rather than directly killing the fungi. - While it can treat onychomycosis, its effectiveness is generally lower, and treatment courses are longer compared to terbinafine. *Amphotericin B* - **Amphotericin B** is an intravenous **antifungal** primarily used for severe systemic fungal infections, not typically for **onychomycosis**. - Its mechanism involves binding to ergosterol in the fungal cell membrane, creating pores and leading to cell lysis. *Clotrimazole* - **Clotrimazole** is an **azole** antifungal primarily used topically for superficial fungal infections like **tinea corporis** or **vaginal candidiasis**. - It is not effective as an oral treatment for onychomycosis due to poor systemic absorption and extensive first-pass metabolism.

Question 1414: Which of the following is NOT a live vaccine?

A. BCG vaccine
B. Measles vaccine
C. Salk vaccine (Correct Answer)
D. Yellow fever vaccine

Explanation: ***Salk vaccine*** - The **Salk vaccine** is an **inactivated (killed)** polio vaccine (IPV), meaning it does not contain live virus. - Inactivated vaccines use killed or inactive forms of pathogens to trigger an immune response without causing disease. *BCG vaccine* - The **BCG (Bacillus Calmette-Guérin) vaccine** is a **live-attenuated vaccine** used to prevent tuberculosis. - Live-attenuated vaccines contain a weakened form of the pathogen, which can replicate but typically doesn't cause disease in healthy individuals. *Measles vaccine* - The **measles vaccine** (often part of the MMR vaccine) is a **live-attenuated vaccine**. - It contains a weakened live measles virus to stimulate a strong, long-lasting immune response. *Yellow fever vaccine* - The **yellow fever vaccine** is a **live-attenuated vaccine** prepared from a weakened strain of the yellow fever virus. - It provides highly effective and long-lasting protection against yellow fever.

Question 1415: Multi-drug resistance tuberculosis implies resistance to at least -

A. Isoniazid and rifampicin (Correct Answer)
B. Rifampicin and ethambutol
C. Isoniazid and ethambutol
D. Resistance to any two antitubercular drugs, excluding isoniazid and rifampicin.

Explanation: ***Isoniazid and rifampicin*** - **Multidrug-resistant TB (MDR-TB)** is specifically defined as resistance to at least both **isoniazid** and **rifampicin**, which are the two most potent first-line anti-TB drugs. - Absence of susceptibility to these two drugs makes treatment significantly more challenging and requires second-line agents. *Rifampicin and ethambutol* - While resistance to **rifampicin** is a criterion for MDR-TB, resistance to **ethambutol** alone (without isoniazid resistance) does not meet the definition of MDR-TB. - **Ethambutol** is a first-line drug but not one of the two core drugs whose resistance defines MDR-TB. *Isoniazid and ethambutol* - Resistance to **isoniazid** is a critical component of MDR-TB, but resistance to **ethambutol** alongside it does not fulfill the definition of MDR-TB unless **rifampicin** resistance is also present. - This combination would be considered **isoniazid-resistant TB**, but not multidrug-resistant. *Resistance to any two antitubercular drugs, excluding isoniazid and rifampicin.* - The definition of MDR-TB specifically requires resistance to **isoniazid** and **rifampicin**. - Resistance to any other two drugs, while problematic, does not qualify as MDR-TB if isoniazid and rifampicin are still effective.

Question 1416: What is the treatment of choice for penicillin-resistant gonorrhea?

A. Erythromycin (a macrolide antibiotic)
B. Ceftriaxone (a third-generation cephalosporin) (Correct Answer)
C. Streptomycin (an aminoglycoside antibiotic)
D. Ciprofloxacin (a fluoroquinolone antibiotic)

Explanation: ***Ceftriaxone (a third-generation cephalosporin)*** - **Ceftriaxone** is the recommended treatment for uncomplicated gonorrhea, including penicillin-resistant strains, given as a single intramuscular dose (500 mg IM). - It works by inhibiting bacterial cell wall synthesis and has excellent activity against *Neisseria gonorrhoeae*. - **Current guidelines recommend dual therapy:** Ceftriaxone plus azithromycin (or doxycycline) to prevent resistance development and cover potential co-infection with *Chlamydia trachomatis*. *Erythromycin (a macrolide antibiotic)* - While macrolides like azithromycin are used in combination with ceftriaxone, **erythromycin alone** is not effective first-line therapy for gonorrhea. - Its primary use in STIs is for chlamydia in specific situations, but not as monotherapy for gonorrhea. *Streptomycin (an aminoglycoside antibiotic)* - **Streptomycin** is an older antibiotic primarily used for tuberculosis and plague, but it is not effective against gonorrhea. - It works by inhibiting protein synthesis but lacks the necessary spectrum and tissue penetration for *Neisseria gonorrhoeae*. *Ciprofloxacin (a fluoroquinolone antibiotic)* - **Ciprofloxacin** was previously used for gonorrhea, but widespread resistance has developed globally, making it unreliable. - Due to high rates of fluoroquinolone resistance, it is **no longer recommended** for empiric treatment of gonorrhea by CDC/WHO guidelines.

Question 1417: What is the drug of choice for controlling pertussis?

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

Explanation: ***Erythromycin*** - **Erythromycin**, a macrolide antibiotic, is the **drug of choice** for treating and controlling pertussis (**whooping cough**), caused by *Bordetella pertussis*. - It is effective in **eradicating the bacteria** from the nasopharynx, reducing infectivity, and potentially shortening the duration of symptoms if administered early in the course of the disease. *Tetracycline* - While tetracyclines have some antibacterial activity, they are **not the first-line treatment** for pertussis due to concerns about side effects, especially in children, and because macrolides are more effective. - **Tetracyclines** can cause **tooth discoloration** and affect bone development in young children and pregnant women. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone antibiotic primarily used for infections caused by Gram-negative bacteria and some Gram-positive bacteria, but it is **not indicated** for pertussis. - Its spectrum of activity and **potential side effects**, including cartilage damage in developing individuals, make it an inappropriate choice for routine pertussis treatment. *Penicillin* - **Penicillin** is effective against many Gram-positive bacteria, but **Bordetella pertussis** is a **Gram-negative bacterium** and is **resistant to penicillin**. - Therefore, penicillin would be **ineffective** in treating or controlling pertussis.

Question 1418: All are false about tigecycline, except:-

A. 90% pseudomonas strains are sensitive
B. It is bactericidal drug
C. It is a broad spectrum antimicrobial (Correct Answer)
D. Dose reduction is required in renal failure

Explanation: ***It is a broad spectrum antimicrobial*** - **Tigecycline** is known for its wide spectrum of activity, effective against a variety of gram-positive, gram-negative, and anaerobic bacteria. - It is particularly useful in treating infections caused by **multidrug-resistant (MDR)** organisms, including MRSA and VRE. *90% pseudomonas strains are sensitive* - Tigecycline generally has **poor activity** against *Pseudomonas aeruginosa*, and its use is specifically cautioned against for such infections. - **Many *Pseudomonas* strains are intrinsically resistant** to tigecycline, making it an unreliable choice for treating these infections. *It is bactericidal drug* - Tigecycline is a **bacteriostatic** antibiotic, meaning it inhibits bacterial growth rather than directly killing bacteria. - It achieves its effect by binding to the **30S ribosomal subunit**, thereby blocking protein synthesis. *Dose reduction is required in renal failure* - **Tigecycline** is primarily eliminated via **biliary and fecal excretion**, with only a small portion excreted renally. - Therefore, **dose adjustments are generally not required** in patients with renal impairment, but caution is usually advised in severe hepatic impairment.

Question 1419: Drug which lacks intrinsic activity against anaerobes is:-

A. Beta lactams
B. Aminoglycosides (Correct Answer)
C. Metronidazole
D. Chloramphenicol

Explanation: ***Aminoglycosides*** - Aminoglycosides require an **oxygen-dependent transport system** to enter bacterial cells and exert their effects. - Due to the **anaerobic environment**, this transport system is inactive, rendering aminoglycosides ineffective against anaerobic bacteria. *Beta lactams* - Many beta-lactam antibiotics, especially certain **cephalosporins (e.g., cefoxitin, cefotetan)** and **carbapenems (e.g., imipenem, meropenem)**, have significant activity against anaerobes. - They inhibit **cell wall synthesis** and are a common choice for infections involving anaerobes. *Metronidazole* - **Metronidazole** is a potent and widely used antibiotic specifically effective against a broad spectrum of **anaerobic bacteria** and protozoa. - It acts by forming **cytotoxic reduced products** that disrupt bacterial DNA synthesis in anaerobic conditions. *Chloramphenicol* - **Chloramphenicol** is a broad-spectrum antibiotic that is highly effective against both aerobic and **anaerobic bacteria**. - It works by binding to the **50S ribosomal subunit**, thereby inhibiting bacterial protein synthesis.

Question 1420: Amphotericin B acts on:-

A. Cell membrane (Correct Answer)
B. Cytoplasm
C. Nucleus
D. Cell wall

Explanation: ***Cell membrane*** Amphotericin B primarily targets the **ergosterol** in the fungal **cell membrane** [1]. It binds to **ergosterol**, forming pores and disrupting the membrane's integrity, leading to leakage of cellular contents and ultimately cell death [1]. *Cytoplasm* The cytoplasm is the internal fluid of the cell where many metabolic processes occur, but it is **not the primary target** of amphotericin B's fungicidal action. While cytoplasmic contents leak out due to membrane damage, the drug does not directly act on cytoplasmic components to exert its effect. *Nucleus* The nucleus contains the genetic material of the fungal cell, but amphotericin B does **not directly interact with nuclear components** or DNA. Damage to the cell membrane is the primary mechanism, with nuclear function only indirectly affected by overall cellular disruption. *Cell wall* Fungal cell walls are composed of **chitin and glucans**, but amphotericin B **does not target these components**. Its action is distinct from drugs that inhibit cell wall synthesis, such as echinocandins.

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