Antimicrobial Agents Practice Questions

Q: What is the drug of choice for treating onychomycosis?

Terbinafine. ***Terbinafine*** - **Terbinafine** is the preferred first-line oral antifungal agent for treating **onychomycosis** due to its high efficacy and favorable safety profile. - It accumulates in the nail plate, providing sustained therapeutic levels that result in high cure rates. *Fluconazole* - While effective against some fungal infections, **fluconazole** is typically a second-line choice for onychomycosis, often reserved for patients who cannot tolerate or prefer not to use terbinafine. - It has a broader spectrum but generally shows lower efficacy for dermatophyte-induced onychomycosis compared to terbinafine. *Nystatin* - **Nystatin** is primarily effective against **Candida** species and is rarely effective against the **dermatophytes** that commonly cause onychomycosis. - It is typically used for topical treatment of mucocutaneous candidiasis and is not suitable for systemic or nail plate penetration. *Itraconazole* - **Itraconazole** is an effective oral antifungal for onychomycosis, often used in a pulse-dosing regimen, but it can have more significant drug interactions and a less favorable safety profile than terbinafine. - It is considered an alternative or second-line agent, especially in cases where terbinafine is not tolerated or effective.

Q: Anaerobes are resistant intrinsically against which of the following?

Aminoglycosides. ***Aminoglycosides*** - **Aminoglycosides** require an **oxygen-dependent transport system** to enter bacterial cells. [3] - Since **anaerobes** thrive in low-oxygen environments, this transport system is inactive, making them intrinsically resistant to aminoglycosides. [3] *Azithromycin* - **Azithromycin** (a macrolide) inhibits protein synthesis by binding to the 50S ribosomal subunit. - Many anaerobes are susceptible to **azithromycin**, making it an effective treatment for certain anaerobic infections. *Metronidazole* - **Metronidazole** is a potent prodrug that requires reduction by **anaerobic metabolism** to become active. [1], [2] - Its mechanism of action involves creating **cytotoxic free radicals** that damage DNA, making it highly effective against most anaerobes. [2] *Beta lactam antibiotics* - **Beta-lactam antibiotics**, such as **penicillins** and **cephalosporins**, interfere with bacterial cell wall synthesis. - While some anaerobes are susceptible, others have developed resistance mechanisms like producing **beta-lactamase enzymes**, but they are not intrinsically resistant across the board. [4]

Q: Burkholderia cepacia is resistant to which of the following antibiotics?

Cefotetan. ***Cefotetan*** - *Burkholderia cepacia* complex is **intrinsically resistant to second-generation cephalosporins** like cefotetan. - This resistance is mediated by **chromosomally encoded AmpC beta-lactamases** and reduced outer membrane permeability. - Second-generation cephalosporins have **no role** in treating *B. cepacia* infections. *Cefepime* - **Cefepime** (fourth-generation cephalosporin) shows **variable activity** against *B. cepacia* complex. - While it has enhanced stability against some beta-lactamases, resistance is common and susceptibility testing is required. - It may be used in some cases but is **not consistently effective**. *Piperacillin-tazobactam* - **Piperacillin-tazobactam** demonstrates **variable and often limited activity** against *B. cepacia* complex. - Susceptibility is strain-dependent and must be confirmed by testing before use. - The tazobactam component does not adequately inhibit the chromosomal beta-lactamases of *B. cepacia*. *Meropenem* - **Meropenem** and other carbapenems show **better but still variable activity** against *B. cepacia* complex. - While historically considered a treatment option, **carbapenem resistance is increasingly common**. - Treatment should be guided by susceptibility testing; ceftazidime, meropenem, and minocycline are among the agents with better (though inconsistent) activity.

Q: Meningococcal polysaccharide vaccine (MPSV4) contains?

50 mcg of polysaccharide of each strain. ***50 mcg of polysaccharide of each strain*** - The **polysaccharide meningococcal vaccine (MPSV4)** contains **50 mcg** of purified capsular polysaccharide from each of the four serogroups (A, C, W-135, and Y). - This specific dosage ensures an adequate immune response without causing excessive reactogenicity. *100 mcg of polysaccharide of each strain* - This dosage is **higher** than the standard concentration found in MPSV4 and is not the correct amount per strain. - Using a higher concentration could potentially increase adverse reactions without significantly enhancing immunogenicity. *1000 mcg of polysaccharide of each strain* - This amount is **significantly higher** than the immunologically effective dose for meningococcal polysaccharides. - Such a high dose would be economically unfeasible and likely lead to higher rates of side effects. *5000 mcg of polysaccharide of each strain* - This is an **extremely high** and impractical dosage for a vaccine. - It would be associated with a high risk of adverse events and would not be used in vaccine formulations.

Q: Rota-teq oral vaccine for rotavirus contains how many reassorted rotaviruses?

5 reassorted rotaviruses. ***5 reassorted rotaviruses*** - **RotaTeq** (RV5) is a pentavalent vaccine containing **five live attenuated human-bovine reassortant rotaviruses**. - These reassortants express four different G serotypes (G1, G2, G3, G4) and one P serotype (P1A[8]), providing broad protection against common rotavirus strains causing severe gastroenteritis. *2 reassorted rotaviruses* - This option is incorrect as **RotaTeq** contains five reassorted rotaviruses, not two. - The number two is not associated with any of the currently available rotavirus vaccines. *3 reassorted rotaviruses* - This option is incorrect. **RotaTeq** does not contain three reassorted rotaviruses. - No major rotavirus vaccine contains exactly three reassorted strains. *4 reassorted rotaviruses* - This option is incorrect. **RotaTeq** specifically contains five reassorted rotaviruses, not four. - While other rotavirus vaccines exist (e.g., Rotarix is monovalent), none are based on four reassorted strains.

Q: Dose of benzathine penicillin G to be given in patients with latent syphilis without penicillin allergy and normal CSF findings is

2.4 million units (mU) IM / week for 3 weeks. ***2.4 million units (mU) IM / week for 3 weeks*** - This is the **standard CDC-recommended regimen** for treating **latent syphilis** in patients without penicillin allergy and normal CSF findings. - The extended duration and specific dosage ensure adequate drug levels to eradicate the infection in its latent phase. *1.8 million units (mU) IM / week for 3 weeks* - This dose is **insufficient** for the treatment of latent syphilis. - Subtherapeutic dosing can lead to treatment failure and progression of the disease. *2.0 million units (mU) IM / week for 3 weeks* - While closer to the correct dose, 2.0 mU is **not the recommended standard** for latent syphilis. - Adherence to established guidelines is crucial for effective treatment of syphilis. *3.0 million units (mU) IM / week for 3 weeks* - This dosage is **higher than necessary** for latent syphilis and could potentially increase the risk of side effects, although usually not severe with single dose. - Overdosing does not offer additional therapeutic benefit for latent syphilis compared to the standard regimen.

Q: Which of the following is most active against slowly dividing tubercular bacilli ?

Rifampicin. ***Rifampicin*** - **Rifampicin** is highly effective against both rapidly and **slowly metabolizing** populations of *Mycobacterium tuberculosis*, including **persister bacilli** within macrophages and caseous lesions. - Its ability to penetrate host cells and kill semi-dormant organisms makes it crucial for shortening treatment duration and preventing relapse. - Among the given options, it has the **best sterilizing activity** against slow-growing tubercular populations. *Isoniazid* - **Isoniazid (INH)** is primarily bactericidal against **rapidly dividing** *Mycobacterium tuberculosis* but has limited activity against slowly dividing or dormant bacilli. - It targets mycolic acid synthesis, which is essential for rapidly growing cells but less critical for metabolically inactive cells. *Streptomycin* - **Streptomycin** primarily targets **rapidly multiplying** extracellular bacilli and has poor activity against intracellular or slowly dividing organisms. - Its action is dependent on active protein synthesis, which is significantly reduced in dormant states. *Ethambutol* - **Ethambutol** is mainly **bacteriostatic** and active against multiplying bacilli, preventing mycobacterial cell wall formation. - It is less effective against dormant or slowly replicating bacteria within caseous lesions.

Q: Topical antifungal of choice for Aspergillus infection of the eye?

Natamycin. ***Natamycin*** - **Natamycin (Natacyn) 5%** is the **only FDA-approved topical antifungal** for ophthalmic use and is the **drug of choice** for fungal keratitis caused by filamentous fungi, including *Aspergillus*. - It is a **polyene antifungal** with excellent activity against *Aspergillus* species and has **good corneal penetration** when applied topically. - Natamycin is considered the **gold standard** for treating *Aspergillus* keratitis and is the **first-line agent** for this condition. *Fluconazole* - **Fluconazole** is a triazole antifungal with **poor activity against *Aspergillus* species**. - It is primarily effective against yeasts like *Candida* species, not filamentous fungi. - Fluconazole has **limited role** in treating *Aspergillus* eye infections and is NOT used as a topical agent for this indication. *Miconazole* - **Miconazole** is an imidazole antifungal with limited use in ophthalmic infections. - It has **poor ocular penetration** and is not considered a first-line agent for *Aspergillus* keratitis. *Clotrimazole* - **Clotrimazole** is primarily used for cutaneous and superficial fungal infections. - It has **limited systemic absorption and poor ocular penetration**, making it unsuitable for *Aspergillus* eye infections. - It is not routinely used as a topical ophthalmic antifungal agent.

Q: For systemic mycosis, fluconazole is preferred over ketoconazole because of:

All of the options. ***All of the options*** Fluconazole is preferred over ketoconazole for systemic mycoses due to multiple superior pharmacological properties: **Greater Efficacy:** - Fluconazole has **excellent bioavailability** (>90% oral) and superior tissue penetration, especially into the CNS and CSF - Highly effective against **Candida species** (including systemic candidiasis) and **Cryptococcus neoformans** (cryptococcal meningitis) - Ketoconazole has poor CNS penetration, making it unsuitable for deep-seated infections **Longer Half-life (t1/2):** - Fluconazole has a **half-life of ~30 hours**, enabling **once-daily dosing** - Ketoconazole has a half-life of ~8 hours, requiring multiple daily doses - Longer half-life improves patient compliance and maintains therapeutic drug levels **Lesser Side Effects:** - Fluconazole has **minimal hepatotoxicity** and is generally well-tolerated - Ketoconazole causes **significant hepatotoxicity** (black box warning) and **endocrine disturbances** by blocking steroid synthesis (gynecomastia, decreased testosterone, adrenal suppression) - Fluconazole does not interfere with steroid hormone synthesis at therapeutic doses **Clinical Practice:** Due to these combined advantages, ketoconazole is now rarely used for systemic mycoses and is primarily reserved for topical applications or specific resistant dermatophyte infections.

Question 1

What is the drug of choice for treating onychomycosis?

Accepted Answer

Terbinafine

Answer

Fluconazole

Answer

Nystatin

Answer

Itraconazole

Question 2

Which of the following statements about vitamin K is correct?

Accepted Answer

Prolonged use of antimicrobials can lead to vitamin K deficiency

Answer

All of the options are true

Answer

Vitamin K acts as an anticoagulant

Answer

The recommended dietary allowance for vitamin K is 200-300 micrograms per day

Question 3

Anaerobes are resistant intrinsically against which of the following?

Accepted Answer

Aminoglycosides

Answer

Azithromycin

Answer

Metronidazole

Answer

Beta lactam antibiotics

Question 4

Burkholderia cepacia is resistant to which of the following antibiotics?

Accepted Answer

Cefotetan

Answer

Cefepime

Answer

Piperacillin-tazobactam

Answer

Meropenem

Question 5

Meningococcal polysaccharide vaccine (MPSV4) contains?

Accepted Answer

50 mcg of polysaccharide of each strain

Answer

100 mcg of polysaccharide of each strain

Answer

1000 mcg of polysaccharide of each strain

Answer

5000 mcg of polysaccharide of each strain

Question 6

Rota-teq oral vaccine for rotavirus contains how many reassorted rotaviruses?

Accepted Answer

5 reassorted rotaviruses

Answer

3 reassorted rotaviruses

Answer

4 reassorted rotaviruses

Answer

2 reassorted rotaviruses

Question 7

Dose of benzathine penicillin G to be given in patients with latent syphilis without penicillin allergy and normal CSF findings is

Accepted Answer

2.4 million units (mU) IM / week for 3 weeks

Answer

1.8 million units (mU) IM / week for 3 weeks

Answer

2.0 million units (mU) IM / week for 3 weeks

Answer

3.0 million units (mU) IM / week for 3 weeks

Question 8

Which of the following is most active against slowly dividing tubercular bacilli ?

Accepted Answer

Rifampicin

Answer

Isoniazid

Answer

Streptomycin

Answer

Ethambutol

Question 9

Topical antifungal of choice for Aspergillus infection of the eye?

Accepted Answer

Natamycin

Answer

Clotrimazole

Answer

Miconazole

Answer

Fluconazole

Question 10

For systemic mycosis, fluconazole is preferred over ketoconazole because of:

Accepted Answer

All of the options

Answer

Lesser side effects

Answer

Greater efficacy

Answer

Longer t1/2

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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