Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1381: Ovicidal drug for scabies is:

A. Permethrin (Correct Answer)
B. DDT
C. BHC
D. Ivermectin

Explanation: ***Permethrin*** - **Permethrin** is the recommended first-line treatment for scabies due to its high efficacy as both a **scabicide** and an **ovicidal agent**, meaning it kills both mites and their eggs. - It works by disrupting the **sodium channel system** causing neurotoxicity in parasitic insects resulting in paralysis and death of the mites. - Applied as 5% cream, it is safe and effective for all age groups including infants. *Ivermectin* - **Ivermectin** is an effective oral alternative for scabies treatment, particularly useful in **crusted scabies** or treatment failures. - However, it has **limited ovicidal activity** and primarily kills adult mites, often requiring a second dose after 1-2 weeks. - Not recommended as first-line for typical scabies when ovicidal activity is desired. *DDT* - **DDT (dichlorodiphenyltrichloroethane)** is an organochlorine insecticide primarily known for its use against mosquitoes and agricultural pests, but it is **not used for treating scabies** in humans. - Its use has been largely restricted due to its **environmental persistence** and potential health risks. *BHC (Lindane)* - **Benzene hexachloride (BHC)**, also known as **lindane**, is an older scabicide that has fallen out of favor due to concerns about **neurotoxicity**, particularly in children and individuals with compromised skin barriers. - While it has some ovicidal properties, its **safety profile** is less favorable compared to permethrin and is no longer recommended as first-line therapy.

Question 1382: True about rotavirus vaccine:

A. Given orally (Correct Answer)
B. Killed vaccine
C. Should be given before 5 years
D. Given subcutaneous

Explanation: ***Given orally*** - Rotavirus vaccines are **live attenuated vaccines** administered orally to stimulate localized immunity in the gastrointestinal tract. - This oral route is crucial for inducing **mucosal immunity**, which is important for protection against rotavirus infection. *Killed vaccine* - The rotavirus vaccine is an **attenuated live vaccine**, meaning it contains weakened forms of the virus, not killed ones. - Live attenuated vaccines generally provide a **stronger and longer-lasting immune response** compared to killed vaccines. *Should be given before 5 years* - The rotavirus vaccine series is recommended to be completed in **infancy**, typically before 8 months of age, depending on the specific vaccine brand and schedule. - Giving the vaccine at too old an age increases the (still very small) risk of **intussusception** and a lack of efficacy. *Given subcutaneous* - Rotavirus vaccines are administered by the **oral route**, not subcutaneously. - The **subcutaneous route** is used for various other vaccines, but not for rotavirus.

Question 1383: Cidofovir is used for intralesional treatment of:

A. EBV
B. Herpes zoster
C. Respiratory papillomatosis (Correct Answer)
D. Granuloma inguinale

Explanation: ***Respiratory papillomatosis*** - Cidofovir is an **antiviral medication** that has shown efficacy in the intralesional treatment of **recurrent respiratory papillomatosis**, reducing the frequency of surgical interventions required. - This condition is caused by the **human papillomavirus (HPV)**, and cidofovir works by inhibiting viral DNA synthesis. *EBV* - **Epstein-Barr virus (EBV)** is primarily associated with infectious mononucleosis, certain lymphomas, and nasopharyngeal carcinoma. - While cidofovir has some in vitro activity against EBV, it is **not the standard or primary treatment** for EBV-related conditions, especially not for intralesional treatment. *Herpes zoster* - **Herpes zoster (shingles)** is caused by the varicella-zoster virus (VZV) and is typically treated with oral antiviral agents like **acyclovir, valacyclovir, or famciclovir**. - Cidofovir is **not a first-line treatment** for herpes zoster, and intralesional treatment is not a common approach for this widespread viral rash. *Granuloma inguinale* - **Granuloma inguinale** (also known as donovanosis) is a **bacterial infection** caused by *Klebsiella granulomatis*. - It is treated with antibiotics like **azithromycin, doxycycline, or ciprofloxacin**, not antiviral medications like cidofovir.

Question 1384: Multi drug resistant tuberculosis is defined as resistance to?

A. Rifampicin and Pyrazinamide
B. INH and Rifampicin (Correct Answer)
C. Resistance to all first line drugs
D. INH and Pyrazinamide

Explanation: ***INH and Rifampicin*** - **Multidrug-resistant tuberculosis (MDR-TB)** is specifically defined by resistance to at least **isoniazid (INH)** and **rifampicin** [1], which are the two most potent first-line anti-TB drugs. - This dual resistance makes treatment significantly more challenging and prolonged compared to drug-susceptible TB. *Rifampicin and Pyrazinamide* - While resistance to these drugs is serious, it does not specifically define MDR-TB unless resistance to **isoniazid** is also present. - **Pyrazinamide** is another first-line drug, but its resistance pattern alone with rifampicin does not meet the MDR-TB criteria. *Resistance to all first-line drugs* - Resistance to all four first-line drugs (isoniazid, rifampicin, pyrazinamide, and ethambutol) [1] is classified as **Extensively Drug-Resistant TB (XDR-TB)**, a more severe form of resistance than MDR-TB. - MDR-TB specifically refers to resistance to **INH and rifampicin**, not necessarily all first-line drugs. *INH and Pyrazinamide* - While resistance to both **isoniazid** and **pyrazinamide** is a concern, it does not meet the definition of MDR-TB. - The definition requires resistance to **rifampicin** in addition to isoniazid.

Question 1385: XDR means extensive drug resistance to

A. Minimum of 1 injectable drug
B. H+R
C. 1 Fluoroquinolone
D. Fluoroquinolone + at least one Group A drug (bedaquiline/linezolid) (Correct Answer)

Explanation: ***Fluoroquinolone + at least one Group A drug (bedaquiline/linezolid)*** - **Extensively drug-resistant (XDR) tuberculosis** is defined by the WHO (2021) as TB with resistance to **rifampicin** (RR-TB baseline), plus resistance to any **fluoroquinolone** (levofloxacin or moxifloxacin), plus resistance to at least one additional **Group A drug** (bedaquiline or linezolid). - This represents the current standard definition emphasizing resistance to the most critical second-line oral agents. - XDR-TB is built upon **MDR-TB** (H+R resistance) with additional resistance patterns that make treatment extremely challenging. *Minimum of 1 injectable drug* - Injectable drug resistance (aminoglycosides, capreomycin) was part of the **old XDR-TB definition** (pre-2021) but is no longer required. - The WHO updated the definition to focus on more effective oral drugs rather than injectables. *H+R* - Resistance to **isoniazid (H)** and **rifampicin (R)** defines **multidrug-resistant (MDR) tuberculosis**, not XDR-TB. - MDR-TB is the foundation upon which XDR-TB is built, but it represents a less severe form of drug resistance. *1 Fluoroquinolone* - While fluoroquinolone resistance is a **necessary component** of XDR-TB, it is **not sufficient alone**. - XDR-TB requires fluoroquinolone resistance **plus** additional resistance to Group A drugs (bedaquiline or linezolid).

Question 1386: Extended-spectrum beta-lactamases (ESBLs) are characterized by activity against all except :

A. Carbapenems (Correct Answer)
B. Oxyimino-cephalosporins
C. Penicillins
D. Cephalosporins

Explanation: ***Carbapenems*** - **Extended-spectrum beta-lactamases (ESBLs)** typically do not hydrolyze **carbapenems**, making these antibiotics generally effective against most ESBL-producing bacteria. - The retention of activity against carbapenems is a key distinction between ESBLs and other beta-lactamases like **carbapenemases**. *Oxyimino-cephalosporins* - ESBLs are specifically named for their ability to hydrolyze and inactivate **oxyimino-cephalosporins**, such as **cefotaxime**, **ceftriaxone**, and **ceftazidime**. - This hydrolysis makes these vital third-generation cephalosporins ineffective for treating infections caused by ESBL-producing organisms. *Penicillins* - ESBLs can effectively hydrolyze and render many **penicillins** inactive, especially those lacking beta-lactamase inhibitors. - This broadens the resistance spectrum beyond just cephalosporins to include common penicillins. *Cephalosporins* - ESBLs primarily confer resistance to a wide range of **cephalosporins**, particularly the **first-, second-, and third-generation agents**. - This resistance is a major clinical challenge, necessitating the use of alternative antibiotic classes.

Question 1387: A patient develops an infection of methicillin resistant Staphylococcus aureus. All of the following can be used to treat this infection except

A. Cotrimoxazole
B. Ciprofloxacin
C. Cefaclor (Correct Answer)
D. Vancomycin

Explanation: ***Cefaclor*** - **Cefaclor** is a second-generation **cephalosporin**, which, like all beta-lactam antibiotics, is ineffective against **MRSA** because **MRSA** produces an altered penicillin-binding protein (PBP2a) encoded by the **mecA** gene. - This altered **PBP2a** has a low affinity for **beta-lactam antibiotics**, rendering them inactive. *Cotrimoxazole* - **Cotrimoxazole** (trimethoprim/sulfamethoxazole) is a commonly used and effective oral antibiotic for treating **MRSA** infections, particularly in outpatient settings. - It inhibits **folate synthesis** in bacteria, an essential pathway for their growth and replication. *Ciprofloxacin* - **Ciprofloxacin** is a **fluoroquinolone antibiotic** that can be used to treat certain **MRSA** infections, although resistance can be an issue. [2] - It works by inhibiting bacterial **DNA gyrase** and **topoisomerase IV**, crucial enzymes for DNA replication. [2] *Vancomycin* - **Vancomycin** is a **glycopeptide antibiotic** that is a first-line treatment for serious **MRSA** infections, especially in hospitalized patients. [1] - It works by inhibiting **bacterial cell wall synthesis** at a different site than beta-lactams, making it effective against **MRSA**. [1]

Question 1388: Drug of choice for pertussis is?

A. Ceftriaxone
B. Penicillin
C. Erythromycin
D. Azithromycin (Correct Answer)

Explanation: ***Azithromycin*** - **Macrolides** are the preferred antibiotics for treating pertussis, and **azithromycin** is favored due to its convenient dosing schedule and lower incidence of gastrointestinal side effects compared to erythromycin. - It works by **inhibiting bacterial protein synthesis**, effectively eradicating *Bordetella pertussis* from the nasopharynx, which reduces contagiousness and helps minimize disease transmission. *Ceftriaxone* - **Ceftriaxone** is a third-generation cephalosporin that is effective against a broad spectrum of bacteria but is **not the drug of choice for pertussis**. - Its mechanism of action involves inhibiting **bacterial cell wall synthesis**, but *Bordetella pertussis* is typically susceptible to macrolides, rather than cephalosporins. *Penicillin* - **Penicillin** is a narrow-spectrum antibiotic that primarily targets gram-positive bacteria and some gram-negative cocci; it is **largely ineffective against *Bordetella pertussis***. - *Bordetella pertussis* is a gram-negative coccobacillus that is not typically sensitive to penicillin, making it an inappropriate treatment choice. *Erythromycin* - While **erythromycin** is a macrolide and can be used for pertussis, it is **often associated with significant gastrointestinal side effects** such as nausea, vomiting, and abdominal cramping due to its motilin receptor agonist activity. - **Azithromycin** is generally preferred over erythromycin due to its better tolerability and once-daily dosing, improving patient adherence.

Question 1389: BCG, True about it -

A. Killed vaccine
B. Subcutaneously given
C. Live vaccine (Correct Answer)
D. Given in positive tubercular patients

Explanation: ***Live vaccine*** - BCG (Bacille-Calmette-Guérin) is a **live attenuated vaccine** derived from a weakened strain of *Mycobacterium bovis*. - This live attenuated form elicits a robust immune response, similar to a natural infection, providing protection against **tuberculosis**. *Killed vaccine* - **Killed vaccines** contain inactivated pathogens that cannot replicate, but still retain their immunogenicity. - BCG is a **live, attenuated** vaccine, meaning the pathogen is still alive but weakened, not killed. *Subcutaneously given* - BCG vaccine is typically administered **intradermally** into the deltoid region, not subcutaneously. - This specific route is crucial for eliciting the desired immune response and local reaction, which includes a **papule** that eventually forms a scar. *Given in positive tubercular patients* - BCG vaccination is generally not recommended for individuals with **active tuberculosis** or latent TB infection. - In these cases, the vaccine would likely not be effective and could potentially cause adverse reactions due to a pre-existing immune response.

Question 1390: All are effective against Tinea versicolor except :

A. Griseofulvin (Correct Answer)
B. Clotrimazole
C. Ketoconazole
D. Fluconazole

Explanation: ***Griseofulvin*** - **Griseofulvin** is primarily effective against **dermatophytes** (tinea infections of the skin, hair, and nails) by interfering with fungal cell division. - It has **no significant activity** against *Malassezia globosa* and *Malassezia furfur*, the yeasts responsible for Tinea versicolor. *Clotrimazole* - **Clotrimazole** is an azole antifungal that inhibits ergosterol synthesis, a key component of the fungal cell membrane. - It is an effective **topical treatment** for Tinea versicolor due to its broad-spectrum antifungal activity against *Malassezia* species. *Ketoconazole* - **Ketoconazole** is another azole antifungal that works by impairing ergosterol synthesis. - It is effective in both **topical** (shampoos, creams) and **oral** forms for treating Tinea versicolor. *Fluconazole* - **Fluconazole** is a systemic azole antifungal that inhibits lanosterol 14-alpha-demethylase, an enzyme involved in ergosterol synthesis. - It is an effective **oral treatment** for widespread or recurrent Tinea versicolor, demonstrating good activity against *Malassezia* species.

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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