Antimicrobial Agents Practice Questions

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

Doxycycline. ***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.

Q: 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 :

Azithromycin. ***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.

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

Terbinafine. ***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.

Q: Which of the following is NOT a live vaccine?

Salk vaccine. ***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.

Q: Multi-drug resistance tuberculosis implies resistance to at least -

Isoniazid and rifampicin. ***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.

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

Ceftriaxone (a third-generation cephalosporin). ***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.

Q: What is the drug of choice for controlling pertussis?

Erythromycin. ***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.

Q: All are false about tigecycline, except:-

It is a broad spectrum antimicrobial. ***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.

Q: Drug which lacks intrinsic activity against anaerobes is:-

Aminoglycosides. ***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.

Q: Amphotericin B acts on:-

Cell membrane. ***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.

Question 1

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

Accepted Answer

Doxycycline

Answer

Co-trimoxazole

Answer

Furazolidone

Answer

Tetracycline

Question 2

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 :

Accepted Answer

Azithromycin

Answer

Levofloxacin

Answer

Amikacin

Answer

Cefazolin

Question 3

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

Accepted Answer

Terbinafine

Answer

Griseofulvin

Answer

Amphotericin B

Answer

Clotrimazole

Question 4

Which of the following is NOT a live vaccine?

Accepted Answer

Salk vaccine

Answer

BCG vaccine

Answer

Measles vaccine

Answer

Yellow fever vaccine

Question 5

Multi-drug resistance tuberculosis implies resistance to at least -

Accepted Answer

Isoniazid and rifampicin

Answer

Rifampicin and ethambutol

Answer

Isoniazid and ethambutol

Answer

Resistance to any two antitubercular drugs, excluding isoniazid and rifampicin.

Question 6

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

Accepted Answer

Ceftriaxone (a third-generation cephalosporin)

Answer

Erythromycin (a macrolide antibiotic)

Answer

Streptomycin (an aminoglycoside antibiotic)

Answer

Ciprofloxacin (a fluoroquinolone antibiotic)

Question 7

What is the drug of choice for controlling pertussis?

Accepted Answer

Erythromycin

Answer

Tetracycline

Answer

Ciprofloxacin

Answer

Penicillin

Question 8

All are false about tigecycline, except:-

Accepted Answer

It is a broad spectrum antimicrobial

Answer

90% pseudomonas strains are sensitive

Answer

It is bactericidal drug

Answer

Dose reduction is required in renal failure

Question 9

Drug which lacks intrinsic activity against anaerobes is:-

Accepted Answer

Aminoglycosides

Answer

Beta lactams

Answer

Metronidazole

Answer

Chloramphenicol

Question 10

Amphotericin B acts on:-

Accepted Answer

Cell membrane

Answer

Cytoplasm

Answer

Nucleus

Answer

Cell wall

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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