Antimicrobial Agents — MCQs

A 2-year-old infant is diagnosed with meningitis. A lumbar puncture reveals numerous neutrophils and gram-positive cocci in pairs that appear encapsulated. She is admitted to the hospital and started on intravenous (IV) beta-lactams. Which of the following targets would most likely play a role in the development of resistance to this antibiotic in the most likely etiologic agent of this child's meningitis?

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1331: Which of the following is the chemoprophylaxis of choice in a person who is on a journey to endemic malarial region?

A. Doxycycline
B. Mefloquine
C. Chloroquine
D. Atovaquone-proguanil (Correct Answer)

Explanation: ***Atovaquone-proguanil*** - **First-line choice** for malaria chemoprophylaxis in travelers to endemic regions according to WHO and CDC guidelines - Highly effective against **drug-resistant *P. falciparum***, including chloroquine and mefloquine-resistant strains - **Excellent tolerability** with minimal side effects compared to other antimalarials - **Convenient dosing schedule**: started 1-2 days before travel and continued for only **7 days after** leaving the endemic area (shorter post-travel duration than alternatives) - Well-tolerated with few contraindications, making it suitable for most travelers *Doxycycline* - Effective alternative for malaria prophylaxis as a **tetracycline antibiotic** - Provides additional protection against **leptospirosis** and traveler's diarrhea - However, associated with **photosensitivity reactions** (sunburn risk), **GI upset**, and **esophageal irritation** - Contraindicated in **pregnancy** and **children <8 years** due to effects on teeth and bone - Requires daily dosing starting 1-2 days before until **4 weeks after travel** (longer duration) *Mefloquine* - Once-weekly dosing offers convenience for long-term travelers - Effective against most *P. falciparum* strains - Major limitation: significant **neuropsychiatric side effects** including anxiety, depression, dizziness, and rarely psychosis - Contraindicated in those with **psychiatric history**, seizure disorders, or cardiac conduction abnormalities - Must be started **2-3 weeks before travel** to assess tolerance *Chloroquine* - Historically the first-line agent but now limited by widespread **chloroquine resistance** - Only effective in few remaining areas with **chloroquine-sensitive *P. vivax*** or *P. falciparum* (parts of Central America, Middle East) - Well-tolerated with once-weekly dosing - Not appropriate for most endemic malarial regions in Africa, Southeast Asia, or South America

Question 1332: Which of the following aminoglycosides is most cochleotoxic:-

A. Streptomycin
B. Amikacin
C. Gentamycin (Correct Answer)
D. Minocycline

Explanation: ***Gentamycin*** - **Gentamycin** is known to be the most **cochleotoxic** aminoglycoside, causing irreversible damage to the hair cells in the cochlea [1]. - This toxicity can lead to **permanent hearing loss** and **tinnitus** due to its selective accumulation in inner ear fluids [2]. *Streptomycin* - While streptomycin can cause ototoxicity, its primary adverse effect is vestibulo-toxicity, affecting **balance** more than hearing [2]. - It mainly targets the hair cells of the semicircular canals and otolithic organs, leading to **vertigo** and ataxia [3]. *Amikacin* - Amikacin is also an ototoxic aminoglycoside but is generally considered **less cochleotoxic** than gentamycin. - Its ototoxic effects are comparable to gentamicin, but it is often reserved for infections resistant to other aminoglycosides. *Minocycline* - Minocycline is a **tetracycline antibiotic**, not an aminoglycoside, and is not associated with significant ototoxicity. - Its side effects typically include photosensitivity, gastrointestinal upset, and **vestibular dysfunction** (dizziness, vertigo) in some patients, distinct from cochlear damage.

Question 1333: Empirical drug of choice for treatment of meningococcal meningitis is:-

A. Cefotetan
B. Cefoxitin
C. Gentamicin
D. Ceftriaxone (Correct Answer)

Explanation: ***Ceftriaxone*** - As a **third-generation cephalosporin**, **Ceftriaxone** provides excellent coverage against common bacterial causes of meningitis, including *Neisseria meningitidis*. - It achieves high concentrations in the **cerebrospinal fluid (CSF)**, making it highly effective for CNS infections. *Cefotetan* - **Cefotetan** is a **second-generation cephalosporin** that has limited CSF penetration and less reliable coverage against common meningitis pathogens. - While it has activity against some gram-negative bacteria, it is not considered a first-line agent for empirical treatment of meningitis. *Cefoxitin* - **Cefoxitin** is also a **second-generation cephalosporin** with limited ability to cross the blood-brain barrier, making it unsuitable for treating meningitis. - Its spectrum of activity is more focused on anaerobic bacteria and some gram-negative organisms, not typically the main culprits in meningitis. *Gentamicin* - **Gentamicin** is an **aminoglycoside antibiotic** that has poor penetration into the CSF and is less effective as a monotherapy for meningitis. - It is often used in combination with other antibiotics, but not as an empirical monotherapy for suspected meningococcal meningitis.

Question 1334: Bivalent HPV vaccine contains which types?

A. Type 6,16
B. Type 11,18
C. Type 16,18 (Correct Answer)
D. Type 6,11

Explanation: ***Type 16,18*** - The **bivalent HPV vaccine** (Cervarix) specifically targets HPV types 16 and 18, which are responsible for the majority of **cervical cancers**. - These two types are considered **high-risk HPV strains** due to their strong oncogenic potential. *Type 6,16* - This combination is partially correct as **HPV 16** is a high-risk type, but **HPV 6** is primarily associated with **genital warts** and is included in the quadrivalent and nonavalent vaccines, not the bivalent. - The bivalent vaccine aims solely for **oncogenic types 16 and 18** for cervical cancer prevention. *Type 11,18* - This combination incorrectly includes **HPV 11**, which, like HPV 6, causes **genital warts** and is not a target of the bivalent vaccine. - While **HPV 18** is a key oncogenic target, HPV 11 does not contribute to the efficacy of the bivalent vaccine against cervical cancer. *Type 6,11* - These HPV types are known to cause approximately 90% of **genital warts** and are considered **low-risk types**, not associated with cervical cancer. - The bivalent vaccine's primary goal is **cervical cancer prevention** by targeting high-risk oncogenic types, rendering this option incorrect.

Question 1335: DOC for Herpes simplex encephalitis:

A. Amphotericin B
B. Intravenous immunoglobulins
C. Inosine pranobex
D. Acyclovir (Correct Answer)

Explanation: ***Acyclovir*** - **Acyclovir** is the drug of choice for treating **Herpes simplex encephalitis (HSE)** due to its potent antiviral activity against **herpes simplex virus (HSV)**. - It works by inhibiting viral DNA synthesis, thereby reducing viral replication and decreasing morbidity and mortality associated with HSE. *Amphotericin B* - **Amphotericin B** is an **antifungal medication** primarily used for severe systemic fungal infections. - It has no antiviral activity against **HSV** and is therefore ineffective in treating **Herpes simplex encephalitis**. *Inosine pranobex* - **Inosine pranobex** is an **immunomodulatory agent** that is sometimes used for viral infections, but it is not the drug of choice for acute, life-threatening conditions like **Herpes simplex encephalitis**. - Its effectiveness for **HSE** is not established, and it cannot replace potent antiviral therapy. *Intravenous immunoglobulins* - **Intravenous immunoglobulins (IVIG)** are used for immune deficiencies or certain autoimmune and inflammatory conditions. - While they can provide passive immunity, **IVIG** are not a primary treatment for acute viral infections like **HSE** and do not directly inhibit viral replication.

Question 1336: Components of acellular pertussis vaccine

A. FHA + Pertactin
B. PT + Pertactin
C. PT + FHA + Pertactin (Correct Answer)
D. PT + FHA + PRN + FIM

Explanation: ***PT + FHA + Pertactin*** - The most common contemporary **acellular pertussis vaccines (DTaP and Tdap)** typically include **detoxified pertussis toxin (PT)**, **filamentous hemagglutinin (FHA)**, and **pertactin (PRN)** as key antigenic components. - These components elicit a protective immune response against *Bordetella pertussis* by targeting virulence factors essential for bacterial adherence and pathogenesis. *FHA + Pertactin* - This option is incomplete as it misses the crucial **pertussis toxin (PT)**, which is a major virulence factor and a primary component of acellular pertussis vaccines. - While FHA and pertactin are important for immunity, they alone are insufficient to provide comprehensive protection against all aspects of pertussis infection. *PT + Pertactin* - This combination is incomplete, as it omits **filamentous hemagglutinin (FHA)**, an important adhesin that contributes significantly to *Bordetella pertussis* colonization and is a standard component of acellular vaccines. - A comprehensive vaccine strategy aims to include multiple antigens to achieve broader and more robust immunity. *PT + FHA + PRN + FIM* - While some research vaccines and earlier formulations might have included **fimbriae (FIM)**, modern and widely available acellular pertussis vaccines (DTaP/Tdap) in many regions primarily rely on **PT, FHA, and pertactin (PRN)** as the core three components. - The inclusion of fimbriae is not universal across all acellular pertussis vaccines currently in use, though some formulations do include FIM types 2 and 3 for enhanced protection.

Question 1337: According to current WHO guidelines, the first-line drug of choice for managing uncomplicated vivax malaria is:

A. Chloroquine (Correct Answer)
B. Clindamycin
C. Artesunate
D. Artemether

Explanation: ***Chloroquine*** - **Chloroquine plus primaquine** remains the **WHO first-line treatment** for uncomplicated *P. vivax* malaria in areas where chloroquine resistance has not been established. - Chloroquine is highly effective against the blood stages of *P. vivax* with **rapid parasite clearance** and excellent tolerability. - In the majority of endemic regions, *P. vivax* remains **chloroquine-sensitive**, making it the preferred first-line agent. - Primaquine is added to eliminate hypnozoites and prevent relapse, but chloroquine remains the primary blood schizonticide. - Only in areas with **documented chloroquine resistance** (parts of Papua New Guinea, Indonesia) does WHO recommend switching to **artemisinin-based combination therapy (ACT)**. *Artesunate* - Artesunate is the cornerstone of **ACTs for *P. falciparum* malaria**, not monotherapy for vivax. - For vivax, artesunate-based ACTs are reserved for **chloroquine-resistant areas** or when used as combination therapy. - While effective, it is **not the first-line choice** globally for uncomplicated vivax malaria where chloroquine remains effective. *Artemether* - Artemether (typically as artemether-lumefantrine) is another ACT option. - Like artesunate, it is used for vivax malaria only in **chloroquine-resistant regions** or for *P. falciparum*. - Not the standard first-line for uncomplicated vivax malaria per WHO guidelines. *Clindamycin* - Clindamycin is used as an **adjunct therapy** in combination with quinine for severe malaria or in special populations (e.g., pregnant women). - It is **never used as monotherapy** and is not a first-line option for uncomplicated vivax malaria.

Question 1338: Drug of choice for roundworm

A. Mebendazole
B. Metronidazole
C. Praziquantel
D. Albendazole (Correct Answer)

Explanation: ***Albendazole*** - **Albendazole** is a broad-spectrum anthelminthic and is the drug of choice for treating common roundworm infections like *Ascaris lumbricoides*. - It works by inhibiting microtubule polymerization in parasitic worms, leading to their immobility and death. *Mebendazole* - **Mebendazole** is also an effective anthelminthic used for roundworm infections, but **albendazole** is generally preferred due to its single-dose efficacy and broader spectrum. - While effective, it may be used as an alternative if albendazole is not available or contraindicated. *Metronidazole* - **Metronidazole** is an antibiotic and antiprotozoal agent used primarily for anaerobic bacterial infections and parasitic protozoa like *Giardia* and *Trichomonas*. - It is **ineffective** against helminthic infections such as roundworms. *Praziquantel* - **Praziquantel** is primarily used to treat infections caused by **flukes** (trematodes) and **tapeworms** (cestodes). - It is **not effective** against roundworms (nematodes).

Question 1339: Standard dose of rifampicin for adults (≥50 kg) in RNTCP is -

A. 600 mg (Correct Answer)
B. 300 mg
C. 100 mg
D. 450 mg

Explanation: ***600 mg*** - For adults weighing **50 kg or more**, the standard daily dose of **rifampicin** under the **Revised National Tuberculosis Control Programme (RNTCP)** is 600 mg. - This dosage is crucial for achieving optimal therapeutic concentrations and ensuring effective treatment of **tuberculosis**. *300 mg* - This is **not a standard RNTCP dose** for any specific weight category in adults. - Administering only 300 mg to an adult weighing ≥50 kg would be a significant **underdose**, leading to treatment failure and potential drug resistance. *100 mg* - 100 mg is a significantly **subtherapeutic dose** for rifampicin in adults, regardless of weight. - Such a low dose would be entirely ineffective in treating tuberculosis and would promote the development of **drug-resistant strains**. *450 mg* - While 450 mg is the correct dose for patients in the **30-49 kg weight band** under RNTCP, it is not the standard dose for individuals weighing 50 kg or more. - Using 450 mg for a patient ≥50 kg would result in **under-dosing**, compromising treatment efficacy.

Question 1340: A 2-year-old infant is diagnosed with meningitis. A lumbar puncture reveals numerous neutrophils and gram-positive cocci in pairs that appear encapsulated. She is admitted to the hospital and started on intravenous (IV) beta-lactams. Which of the following targets would most likely play a role in the development of resistance to this antibiotic in the most likely etiologic agent of this child's meningitis?

A. Reverse transcriptase
B. Penicillin-binding protein (Correct Answer)
C. Bactoprenol
D. DNA gyrase

Explanation: ***Penicillin-binding protein*** - The most likely pathogen causing meningitis in a 2-year-old with gram-positive cocci in pairs and capsules is *Streptococcus pneumoniae*. Resistance in *S. pneumoniae* to beta-lactam antibiotics (like penicillin and cephalosporins) primarily arises from **mutations in its penicillin-binding proteins (PBPs)**, which reduce their affinity for these drugs. - Beta-lactam antibiotics exert their effect by binding to and inactivating bacterial **PBPs**, which are essential for **cell wall synthesis**. *Reverse transcriptase* - **Reverse transcriptase** is an enzyme found in **retroviruses** and is involved in converting RNA into DNA; it is not present in bacteria. - This target is associated with resistance to **antiretrovirals** (e.g., in HIV treatment), not bacterial antibiotics. *Bactoprenol* - **Bactoprenol** is a lipid carrier molecule involved in the transport of peptidoglycan precursors across the bacterial cell membrane for cell wall synthesis. - While crucial for cell wall synthesis, it is not a direct target for beta-lactam antibiotics, nor is it the primary mechanism for beta-lactam resistance in *S. pneumoniae*. *DNA gyrase* - **DNA gyrase** is a bacterial enzyme responsible for relieving supercoiling during DNA replication. - It is the primary target for **fluoroquinolone antibiotics**, and mutations in DNA gyrase can lead to fluoroquinolone resistance, but it is not relevant to beta-lactam resistance.

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

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Principles of Antimicrobial Selection

Practice Questions

Antimicrobial Resistance

Practice Questions

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