Antimicrobial Agents Practice Questions

Q: What is the drug that can be used for rheumatic fever prophylaxis in a patient with a history of allergy to Penicillin?

Erythromycin. ***Erythromycin*** - **Erythromycin** is a macrolide antibiotic that is a suitable alternative for **rheumatic fever prophylaxis** in patients with a documented allergy to penicillin. - It effectively covers *Streptococcus pyogenes*, the causative agent of group A streptococcal (GAS) pharyngitis that precedes rheumatic fever. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic and would be contraindicated in a patient with a **penicillin allergy**, as it carries a high risk of cross-reactivity and allergic reaction. - Using amoxicillin in this scenario could lead to severe hypersensitivity reactions, compromising patient safety. *Streptomycin* - **Streptomycin** is an aminoglycoside antibiotic primarily used for infections like **tuberculosis** and severe bacterial endocarditis. - It is not indicated for the treatment of *Streptococcus pyogenes* infections or for **rheumatic fever prophylaxis**. *Sulfasalazine* - **Sulfasalazine** is an anti-inflammatory and immunomodulatory drug primarily used in the management of **inflammatory bowel disease** and **rheumatoid arthritis**. - It has no antimicrobial activity against *Streptococcus pyogenes* and is therefore not used for **rheumatic fever prophylaxis**.

Q: Red man syndrome is caused by

Vancomycin. ***Vancomycin*** - **Red man syndrome** is a well-known adverse reaction associated with **rapid intravenous infusion** of vancomycin. - It results from the **non-IgE mediated release of histamine** from mast cells and basophils. *Ciprofloxacin* - This antibiotic belongs to the **fluoroquinolone** class and is primarily associated with side effects such as **tendon rupture**, **QT prolongation**, and **GI disturbances**, not red man syndrome. - Ciprofloxacin has a different mechanism of action and adverse effect profile compared to vancomycin. *Teicoplanin* - While **teicoplanin** is a glycopeptide antibiotic similar to vancomycin, it is much **less likely** to cause red man syndrome due to its different molecular structure and slower histamine-releasing potential. - It generally has a more favorable safety profile regarding infusion-related reactions. *Amikacin* - **Amikacin** is an **aminoglycoside** antibiotic known for side effects like **ototoxicity** and **nephrotoxicity**. - It does not cause red man syndrome, as its mechanism of action and adverse effects are distinctly different from vancomycin.

Q: A patient was given chloroquine and doxycycline for 7 days. The patient's fever decreased in 4 days, but on day 6, parasitemia recurred with reappearance of asexual forms of Plasmodium falciparum on peripheral smear. This type of drug resistance is?

R1 type. ***R1 type*** - **R1 resistance (Resistance level I)** is characterized by **initial clearance or marked reduction of asexual parasitemia followed by recrudescence within 7 days** of treatment initiation. - In this case, the fever decreased (indicating initial parasite suppression), but asexual forms reappeared on day 6, fulfilling the criteria for R1 resistance. - This represents **partial drug sensitivity** where parasites are initially suppressed but not completely eliminated. *R2 type* - **R2 resistance (Resistance level II)** involves **marked reduction but not complete clearance** of asexual parasitemia during treatment. - Parasites remain detectable throughout treatment without an initial period of clearance. - This patient showed initial improvement with subsequent recrudescence, which is characteristic of R1, not R2. *R3 type* - **R3 resistance (Resistance level III)** signifies **complete failure of treatment with no reduction** in asexual parasite count. - This patient's fever decreased in 4 days, indicating at least partial response, ruling out R3 resistance. *R4 type* - **R4 is not a recognized category** in the WHO classification of antimalarial drug resistance. - The standard WHO classification includes only **R1, R2, and R3 resistance levels** based on asexual parasite response to treatment.

Q: Cidofovir is used for intralesional treatment of:

Respiratory papillomatosis. ***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.

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

Cefaclor. ***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]

Q: Drug of choice for pertussis is?

Azithromycin. ***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.

Q: All are effective against Tinea versicolor except :

Griseofulvin. ***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.

Q: Leprosy is made non-infectious by Rifampicin in:

2 weeks. ***2 weeks*** - Rifampicin is a potent bactericidal drug against **Mycobacterium leprae**, rapidly reducing the bacterial load and rendering the patient **non-infectious within approximately 2 weeks of initiation**. - This quick action is crucial for **breaking the chain of transmission** in leprosy, allowing patients to resume normal social activities with a lower risk of spreading the disease. *3 weeks* - While treatment duration for leprosy can extend to months or years, the specific action of Rifampicin in rendering a patient non-infectious is known to occur earlier, typically before 3 weeks. - The goal is rapid reduction in infectivity, which Rifampicin achieves quicker than 3 weeks. *4 weeks* - Four weeks (one month) is a longer duration than required for Rifampicin to effectively render a patient non-infectious, as its bactericidal action is much faster. - Delaying isolation or protective measures for this long would be unnecessary, given Rifampicin's rapid effect. *1 week* - Although Rifampicin acts rapidly, **a full week may not be sufficient for complete cessation of infectivity**, though significant reduction occurs within this timeframe. - The widely accepted timeframe for reliable non-infectivity is closer to 2 weeks for leprosy.

Q: Griseofulvin is used in –

Tinea capitis. ***Tinea capitis*** - **Griseofulvin** is an oral antifungal agent specifically effective against **dermatophytes**, which cause **tinea infections**, including **tinea capitis**. - It works by interfering with **microtubule function**, inhibiting fungal cell division and growth. *P. versicolor* - **P. versicolor (Malassezia furfur)** is the causative agent of **pityriasis versicolor**, a superficial fungal infection. - While Griseofulvin is active against dermatophytes, it is **not the primary treatment** for pityriasis versicolor; topical antifungals or oral azoles like fluconazole are usually preferred. *Candidiasis* - **Candidiasis** is caused by **Candida species**, primarily **Candida albicans**. - Griseofulvin has **no significant activity** against Candida; other antifungals like azoles, polyenes, or echinocandins are used for Candidiasis. *All of the options* - This option is incorrect because Griseofulvin is effective only against **dermatophytes** and not against *P. versicolor* or Candidiasis. - Its narrow spectrum of activity makes it unsuitable for all the conditions listed.

Q: Which one of the following antibiotic is not recommended for lactating mothers?

Quinolones. ***Quinolones*** - **Quinolones** are generally **not recommended** for lactating mothers due to concerns about potential harm to the infant's developing **cartilage** and **joints**. - They have been associated with **arthropathies** and **tendinopathies** in animal studies and young patients, leading to caution in this population. *Aminoglycoside* - **Aminoglycosides** are typically considered **safe** in lactation because they have **poor oral absorption** by the infant, meaning very little drug reaches the infant's systemic circulation. - While they can be excreted into breast milk, the amount absorbed by the infant is usually **negligible**, reducing risk of toxicity. *Cephalosporins* - **Cephalosporins** are generally considered **safe** for lactating mothers as they are excreted into breast milk in **low concentrations** and have a good safety profile for infants. - Potential side effects in the infant are usually minor, such as **diarrhea** or **thrush**, and serious adverse events are rare. *Anti tubercular drugs* - Most **first-line anti-tubercular drugs** (e.g., isoniazid, rifampicin, ethambutol, pyrazinamide) are generally **considered compatible** with breastfeeding. - While they do pass into breast milk, the benefits of treating **maternal tuberculosis** and preventing transmission to the infant usually outweigh the theoretical risks.

Question 1

What is the drug that can be used for rheumatic fever prophylaxis in a patient with a history of allergy to Penicillin?

Accepted Answer

Erythromycin

Answer

Amoxicillin

Answer

Streptomycin

Answer

Sulfasalazine

Question 2

Red man syndrome is caused by

Accepted Answer

Vancomycin

Answer

Ciprofloxacin

Answer

Teicoplanin

Answer

Amikacin

Question 3

A patient was given chloroquine and doxycycline for 7 days. The patient's fever decreased in 4 days, but on day 6, parasitemia recurred with reappearance of asexual forms of Plasmodium falciparum on peripheral smear. This type of drug resistance is?

Accepted Answer

R1 type

Answer

R3 type

Answer

R4 type

Answer

R2 type

Question 4

Cidofovir is used for intralesional treatment of:

Accepted Answer

Respiratory papillomatosis

Answer

EBV

Answer

Herpes zoster

Answer

Granuloma inguinale

Question 5

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

Accepted Answer

Cefaclor

Answer

Cotrimoxazole

Answer

Ciprofloxacin

Answer

Vancomycin

Question 6

Drug of choice for pertussis is?

Accepted Answer

Azithromycin

Answer

Ceftriaxone

Answer

Penicillin

Answer

Erythromycin

Question 7

All are effective against Tinea versicolor except :

Accepted Answer

Griseofulvin

Answer

Clotrimazole

Answer

Ketoconazole

Answer

Fluconazole

Question 8

Leprosy is made non-infectious by Rifampicin in:

Accepted Answer

2 weeks

Answer

3 weeks

Answer

4 weeks

Answer

1 week

Question 9

Griseofulvin is used in –

Accepted Answer

Tinea capitis

Answer

P. versicolor

Answer

Candidiasis

Answer

All of the options

Question 10

Which one of the following antibiotic is not recommended for lactating mothers?

Accepted Answer

Quinolones

Answer

Aminoglycoside

Answer

Cephalosporins

Answer

Anti tubercular drugs

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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