Antimicrobial Agents Practice Questions

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.

Q: Agents most effective and best tolerated in the management of onychomycosis?

Itraconazole and terbinafine. ***Itraconazole and terbinafine*** - **Terbinafine** is a highly effective **allylamine antifungal** for onychomycosis, achieving high cure rates with good tolerability due to its fungicidal action and accumulation in the nail plate. - **Itraconazole** is a **triazole antifungal** that is also effective for onychomycosis, particularly for both dermatophyte and non-dermatophyte infections, and can be given in pulse doses which may improve patient compliance and reduce side effects. *Ciclopirox and griseofulvin* - **Ciclopirox** is a topical agent, generally less effective for moderate to severe onychomycosis, and requires prolonged daily application. - **Griseofulvin** has a lower cure rate for onychomycosis compared to newer antifungals like terbinafine and itraconazole, and requires longer treatment durations with potential for more drug interactions. *Griseofulvin and ketoconazole* - **Griseofulvin** has been largely supplanted by newer antifungals due to its lower efficacy and longer treatment courses for onychomycosis. - **Ketoconazole** has a less favorable safety profile (e.g., hepatotoxicity) for systemic use in onychomycosis and is generally not recommended as a first-line treatment. *Griseofulvin and caspofungin* - **Griseofulvin** is an older oral antifungal with limited efficacy and prolonged treatment duration for onychomycosis. - **Caspofungin** is an **echinocandin** antifungal primarily used for systemic candidiasis and aspergillosis, and is not indicated for the treatment of onychomycosis.

Q: Cilastatin is given in combination with Imipenem because:-

Cilastatin prevents degradation of Imipenem in kidney. ***Cilastatin prevents degradation of Imipenem in kidney*** - **Imipenem** is extensively metabolized in the renal tubules by the enzyme **dihydropeptidase-I**, leading to its inactivation and potential nephrotoxicity. - **Cilastatin** is a **dihydropeptidase-I inhibitor** that prevents this enzymatic breakdown, increasing the bioavailability and efficacy of imipenem and reducing the risk of renal damage. *Inhibits the enzymes that digest Imipenem in stomach* - **Imipenem** is a parenteral antibiotic and is not administered orally; therefore, degradation in the stomach is not a relevant concern. - Its combination with cilastatin is specifically to address renal metabolism, not gastric degradation. *Cilastatin increase absorption of Imipenem* - **Cilastatin** does not enhance the absorption of imipenem; its role is primarily to inhibit renal metabolism. - Imipenem is administered intravenously, bypassing the need for gastrointestinal absorption. *Reduces side effects of Imipenem* - While cilastatin does prevent the formation of nephrotoxic metabolites of imipenem, its primary role is to **maintain therapeutic levels** and prevent drug inactivation. - The reduction in **nephrotoxicity** is a consequence of preventing degradation, rather than a direct mitigation of general side effects.

Q: In the treatment of granuloma inguinale, which antibiotic regimen is most appropriate?

Doxycycline 100mg BD until lesions heal. ***Doxycycline 100mg BD until lesions heal*** - **Doxycycline** is the recommended first-line treatment for **granuloma inguinale** (donovanosis) due to its effectiveness against **Klebsiella granulomatis**, the causative agent. - Treatment should continue until all lesions have completely healed, which may take at least 3 weeks or longer, to prevent relapse. *Ceftriaxone 250mg IM single dose* - This regimen is typically used for the treatment of **gonorrhea**, not granuloma inguinale. - While effective for some bacterial infections, it is not the appropriate therapy for **Klebsiella granulomatis**. *Azithromycin single dose 1g* - A single 1g dose of **azithromycin** is the standard treatment for **Chlamydia trachomatis** infections. - While azithromycin IS an alternative treatment for granuloma inguinale, it requires **1g weekly or 500mg daily** for at least 3 weeks, not a single dose. - The single-dose regimen shown here is therefore inappropriate for granuloma inguinale. *Penicillin G 2.4 million units IM* - This dosage of **penicillin G** is specifically used to treat **syphilis**, particularly early-stage syphilis. - It has no role in the treatment of granuloma inguinale.

Q: Drug of choice for scrub typhus is:

Doxycycline. ***Doxycycline*** - **Doxycycline** is the drug of choice for **scrub typhus** in both adults and children due to its high efficacy. - It is a **tetracycline antibiotic** that inhibits bacterial protein synthesis, providing broad-spectrum coverage against *Orientia tsutsugamushi*. *Ciprofloxacin* - **Ciprofloxacin** is a **fluoroquinolone antibiotic** primarily used for bacterial infections, but it is **not effective** against *Orientia tsutsugamushi*. - It is generally reserved for specific conditions like urinary tract infections or some severe bacterial infections where other antibiotics are ineffective. *Azithromycin* - **Azithromycin** is a **macrolide antibiotic** that can be used as an alternative therapy for **scrub typhus**, especially in **pregnant women** and young children where doxycycline is contraindicated. - While effective, it is considered a **second-line agent** after doxycycline due to potentially slower resolution of symptoms. *Chloramphenicol* - **Chloramphenicol** was historically used for scrub typhus and is still effective, but its use is limited due to potential **severe side effects** like **bone marrow suppression** and **aplastic anemia**. - Due to these significant toxicities, it is generally reserved for cases where other safer and equally effective antibiotics are contraindicated or ineffective.

Question 1

What is the drug of choice for controlling pertussis?

Accepted Answer

Erythromycin

Answer

Tetracycline

Answer

Ciprofloxacin

Answer

Penicillin

Question 2

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 3

Drug which lacks intrinsic activity against anaerobes is:-

Accepted Answer

Aminoglycosides

Answer

Beta lactams

Answer

Metronidazole

Answer

Chloramphenicol

Question 4

Amphotericin B acts on:-

Accepted Answer

Cell membrane

Answer

Cytoplasm

Answer

Nucleus

Answer

Cell wall

Question 5

DOC for prophylaxis against Diphtheria is:-

Accepted Answer

Erythromycin

Answer

Cloxacillin

Answer

Rifampicin

Answer

Ciprofloxacin

Question 6

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

Accepted Answer

Cloxacillin

Answer

Cefazolin

Answer

Ampicillin

Answer

Metronidazole

Question 7

Agents most effective and best tolerated in the management of onychomycosis?

Accepted Answer

Itraconazole and terbinafine

Answer

Ciclopirox and griseofulvin

Answer

Griseofulvin and ketoconazole

Answer

Griseofulvin and caspofungin

Question 8

Cilastatin is given in combination with Imipenem because:-

Accepted Answer

Cilastatin prevents degradation of Imipenem in kidney

Answer

Inhibits the enzymes that digest Imipenem in stomach

Answer

Reduces side effects of Imipenem

Answer

Cilastatin increases absorption of Imipenem

Question 9

In the treatment of granuloma inguinale, which antibiotic regimen is most appropriate?

Accepted Answer

Doxycycline 100mg BD until lesions heal

Answer

Ceftriaxone 250mg IM single dose

Answer

Azithromycin single dose 1g

Answer

Penicillin G 2.4 million units IM

Question 10

Drug of choice for scrub typhus is:

Accepted Answer

Doxycycline

Answer

Ciprofloxacin

Answer

Azithromycin

Answer

Chloramphenicol

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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