Antimicrobial Agents Practice Questions

Q: A person wants to visit a malaria endemic area of low level chloroquine resistant falciparum malaria. The best chemoprophylaxis is -

Atovaquone + Proguanil. ***Atovaquone + Proguanil*** - **Atovaquone + Proguanil (Malarone)** is the **preferred first-line chemoprophylaxis** for areas with **chloroquine-resistant *P. falciparum***, including low-level resistance. - It has **excellent efficacy** against resistant strains with minimal documented resistance, and is **well-tolerated** with fewer side effects compared to mefloquine. - Approved by WHO and CDC as a **primary option** for travelers to chloroquine-resistant malaria areas. - The daily dosing regimen, while requiring more frequent administration, actually allows for a **shorter pre-travel start time** (1-2 days before vs. 1-2 weeks for mefloquine) and **shorter post-travel duration** (7 days vs. 4 weeks). *Mefloquine* - While **effective against chloroquine-resistant *P. falciparum***, mefloquine is increasingly used as a **second-line option** due to significant **neuropsychiatric side effects** (anxiety, depression, vivid dreams, rarely psychosis). - It requires weekly dosing starting 2 weeks before travel and continuing 4 weeks after, making the total prophylaxis period longer. - **Contraindicated** in individuals with psychiatric disorders, seizure disorders, or cardiac conduction abnormalities. *Sulfadoxine + Pyrimethamine* - This combination is primarily used for **intermittent preventive treatment (IPT)** in pregnant women and infants in endemic areas, **not for travel prophylaxis**. - Widespread **parasitic resistance** to both components has made it unreliable for chemoprophylaxis in most regions. - Not recommended by international guidelines for routine traveler prophylaxis. *Chloroquine* - **Completely ineffective** in areas with **chloroquine-resistant *P. falciparum*** as stated in the question. - Would provide **no protection** and lead to treatment failure if infection occurs.

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 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: 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.

Q: DOC for prophylaxis against Diphtheria is:-

Erythromycin. ***Erythromycin*** - **Erythromycin** is the drug of choice for prophylaxis and treatment of diphtheria, especially in individuals exposed to a confirmed case. - It works by inhibiting protein synthesis in *Corynebacterium diphtheriae*, preventing bacterial multiplication and toxin production. *Cloxacillin* - **Cloxacillin** is a narrow-spectrum penicillinase-resistant penicillin primarily used for treating staphylococcal infections. - It is not effective against *Corynebacterium diphtheriae* and therefore not used for diphtheria prophylaxis. *Rifampicin* - **Rifampicin** is an antibiotic commonly used for tuberculosis and prophylaxis against meningococcal disease. - It does not have significant activity against *Corynebacterium diphtheriae* and is not indicated for diphtheria prevention. *Ciprofloxacin* - **Ciprofloxacin** is a fluoroquinolone antibiotic with a broad spectrum of activity against many bacterial infections. - While it can be used for some respiratory infections, it is not the recommended antibiotic for diphtheria prophylaxis.

Q: Which of the following is the first line drug for mastitis?

Cloxacillin. ***Cloxacillin*** - **Cloxacillin** is a penicillinase-resistant penicillin, making it effective against **Staphylococcus aureus**, the most common causative organism of mastitis. - It is the **first-line oral antibiotic** for treating mastitis in patients without penicillin allergy. - As a penicillin derivative, it should be **avoided in penicillin-allergic patients**, who may be treated with cephalosporins (if no cross-reactivity) or macrolides instead. *Cefazolin* - **Cefazolin** is a first-generation cephalosporin, typically administered intravenously. While effective against methicillin-sensitive *S. aureus*, it is not the first-line oral treatment for mastitis. - It is usually reserved for hospitalized patients or those needing parenteral therapy, not for initial outpatient management. *Ampicillin* - **Ampicillin** is a penicillin antibiotic that is susceptible to degradation by beta-lactamases produced by many *Staphylococcus aureus* strains. - It is generally **not effective** against beta-lactamase-producing *S. aureus*, which is the predominant pathogen in mastitis. *Metronidazole* - **Metronidazole** is an antibiotic primarily effective against **anaerobic bacteria** and certain **parasites**. - It has **no significant activity** against aerobic bacteria like *Staphylococcus aureus*, making it inappropriate for treating typical bacterial mastitis.

Question 1

A person wants to visit a malaria endemic area of low level chloroquine resistant falciparum malaria. The best chemoprophylaxis is -

Accepted Answer

Atovaquone + Proguanil

Answer

Sulfadoxine + Pyrimethamine

Answer

Mefloquine

Answer

Chloroquine

Question 2

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 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

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 5

What is the drug of choice for controlling pertussis?

Accepted Answer

Erythromycin

Answer

Tetracycline

Answer

Ciprofloxacin

Answer

Penicillin

Question 6

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 7

Drug which lacks intrinsic activity against anaerobes is:-

Accepted Answer

Aminoglycosides

Answer

Beta lactams

Answer

Metronidazole

Answer

Chloramphenicol

Question 8

Amphotericin B acts on:-

Accepted Answer

Cell membrane

Answer

Cytoplasm

Answer

Nucleus

Answer

Cell wall

Question 9

DOC for prophylaxis against Diphtheria is:-

Accepted Answer

Erythromycin

Answer

Cloxacillin

Answer

Rifampicin

Answer

Ciprofloxacin

Question 10

Which of the following is the first line drug for mastitis?

Accepted Answer

Cloxacillin

Answer

Cefazolin

Answer

Ampicillin

Answer

Metronidazole

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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