Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1361: Inactivated SA 14-14-2 vaccine is an example of which type of vaccine?

A. Toxoid vaccine
B. Live attenuated vaccine (Correct Answer)
C. Inactivated vaccine
D. Subunit vaccine

Explanation: ***Live attenuated vaccine*** - The **SA 14-14-2 vaccine** is a **live attenuated Japanese Encephalitis (JE) vaccine** developed through serial passage and attenuation of the wild-type SA 14 strain. - The designation "14-14-2" refers to the specific **attenuated strain** after multiple passages, not to an inactivation process. - This vaccine uses **weakened (attenuated) virus** that can replicate minimally, providing robust and long-lasting immunity similar to natural infection. - It is widely used in **China, India, and other Asian countries** in national immunization programs. *Inactivated vaccine* - While there is also an **inactivated version** of the SA 14-14-2 strain (vero cell-derived inactivated JE vaccine), the term "SA 14-14-2 vaccine" by itself typically refers to the **live attenuated formulation**. - Inactivated vaccines contain killed viral particles that cannot replicate. *Toxoid vaccine* - **Toxoid vaccines** are based on inactivated bacterial toxins (toxoids), not viral antigens. - Examples include vaccines for **tetanus** and **diphtheria**, which target toxins produced by bacteria. - This type does not apply to viral vaccines like Japanese Encephalitis. *Subunit vaccine* - **Subunit vaccines** contain only specific purified antigenic components (proteins, polysaccharides) rather than whole organisms. - Examples include **Hepatitis B vaccine** (HBsAg) and **HPV vaccine**. - The SA 14-14-2 vaccine uses the whole attenuated virus, not subunits.

Question 1362: Which of the following antifungal agents is primarily used topically?

A. Itraconazole
B. Griseofulvin
C. Voriconazole
D. Nystatin (Correct Answer)

Explanation: ***Nystatin*** - **Nystatin** is commonly used as a **topical** or **oral swish-and-swallow** antifungal agent for candidal infections of the skin, mucous membranes, and gastrointestinal tract. - It works by binding to **ergosterol** in fungal cell membranes, leading to pore formation and cell death. *Itraconazole* - **Itraconazole** is an **oral** or **intravenous** antifungal agent primarily used for systemic fungal infections or onychomycosis, not typically for topical application. - It works by inhibiting **cytochrome P450-dependent enzymes**, which are essential for ergosterol synthesis. *Griseofulvin* - **Griseofulvin** is an **oral** antifungal used to treat dermatophyte infections of the skin, hair, and nails, especially when topical treatments are ineffective. - It binds to **keratin** in newly formed tissue, making it resistant to fungal invasion. *Voriconazole* - **Voriconazole** is a broad-spectrum **systemic (oral or IV)** antifungal agent, particularly useful for invasive aspergillosis and other serious fungal infections. - It is a **triazole antifungal** that inhibits fungal cytochrome P450 enzymes involved in ergosterol synthesis.

Question 1363: Which of the following is effective against Pseudomonas and is used in burns patients?

A. Silver sulfadiazine (Correct Answer)
B. Sulphadoxine
C. Sulphamethoxazole
D. Silver sulphazine

Explanation: ***Silver sulfadiazine*** - This antimicrobial agent is widely recognized for its effectiveness against a broad spectrum of bacteria, including **Pseudomonas aeruginosa**, a common pathogen in **burn wounds**. - Its mechanism involves the gradual release of **silver ions** and **sulfadiazine**, which together inhibit bacterial growth and prevent infection in burn patients. *Sulphadoxine* - Sulphadoxine is a **long-acting sulfonamide antibiotic** primarily used in combination with pyrimethamine for the treatment of **malaria**. - It does not have a primary role in the topical management of **burn wounds** or specific efficacy against **Pseudomonas**. *Sulphamethoxazole* - Sulphamethoxazole is a **medium-acting sulfonamide** commonly combined with trimethoprim (**co-trimoxazole**) to treat various bacterial infections, including **urinary tract infections** and respiratory infections. - While it has antibacterial properties, it is not typically used topically for **burns** and is not specifically favored for **Pseudomonas** coverage in this context. *Silver sulphazine* - This is a **non-existent medication** - a deliberate distractor with incorrect spelling. - The correct medication is **silver sulfadiazine** (not "sulphazine"), making this a common exam trap to test precise knowledge of antimicrobial nomenclature.

Question 1364: What is the recommended drug for treatment of mild leptospirosis?

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

Explanation: ***Tetracycline (Doxycycline)*** - **Doxycycline** (a tetracycline antibiotic) is the **first-line treatment for mild leptospirosis** - It has excellent activity against **spirochetes** including *Leptospira* species - Typically given as **doxycycline 100 mg twice daily for 7 days** - Also effective as **prophylaxis** in high-risk exposures - Alternative oral agents include **amoxicillin** or **ampicillin** for mild cases *Penicillin* - While **penicillin** is highly effective against *Leptospira*, this specifically refers to **IV Penicillin G for severe leptospirosis** - For **severe disease with organ involvement**, IV Penicillin G (1.5 million units every 6 hours) is the drug of choice - Oral penicillins (amoxicillin/ampicillin) can be used for mild cases but doxycycline is generally preferred - The question asks about general treatment, where **doxycycline is the standard first-line choice for mild cases** *Erythromycin* - Erythromycin is **not recommended** as primary treatment for leptospirosis - It has **poor activity** against *Leptospira* compared to tetracyclines and beta-lactams - Not included in standard treatment guidelines for this infection *Azithromycin* - Azithromycin has **limited documented efficacy** in leptospirosis - It is **not a first-line agent** and is not routinely recommended in treatment guidelines - May be considered as an alternative in specific situations with allergies, but tetracyclines or penicillins are strongly preferred

Question 1365: A diabetic patient developed cellulitis due to S. aureus, which was found to be methicillin resistant on the antibiotic sensitivity testing. All of the following antibiotics will be appropriate except ?

A. Vancomycin
B. Teicoplanin
C. Linezolid
D. Imipenem (Correct Answer)

Explanation: ***Imipenem*** - **Imipenem** is a carbapenem antibiotic that is effective against many Gram-positive and Gram-negative bacteria, but it is **not active against MRSA (methicillin-resistant *Staphylococcus aureus*)**. - MRSA strains are resistant to all beta-lactam antibiotics, including penicillins, cephalosporins, and carbapenems like imipenem, due to the presence of the **mecA gene** which encodes for an altered penicillin-binding protein (PBP2a). *Vancomycin* - **Vancomycin** is a glycopeptide antibiotic that is a primary choice for treating **MRSA infections**, including cellulitis. - It inhibits cell wall synthesis by binding to the D-Ala-D-Ala precursor, preventing cross-linking, and is specifically active against **Gram-positive bacteria**. *Teicoplanin* - **Teicoplanin** is another glycopeptide antibiotic, similar to vancomycin, and is also considered a suitable agent for treating **MRSA infections**. - It works by inhibiting bacterial cell wall synthesis and has a **longer half-life** than vancomycin, allowing for less frequent dosing. *Linezolid* - **Linezolid** is an oxazolidinone antibiotic known for its activity against **Gram-positive bacteria**, including **MRSA** and vancomycin-resistant enterococci (VRE). - It inhibits protein synthesis by binding to the 50S ribosomal subunit, preventing the formation of the initiation complex.

Question 1366: Ivermectin is indicated in the treatment of:

A. Scabies (Correct Answer)
B. Dermatophytosis
C. Tuberculosis
D. Syphilis

Explanation: ***Scabies*** - **Ivermectin** is an effective oral antiparasitic agent used to treat **scabies**, particularly in cases of widespread infestation, crusted scabies, or when topical treatments fail. - It acts by paralyzing and killing the **Sarcoptes scabiei mites** responsible for the infestation. *Dermatophytosis* - **Dermatophytosis** (ringworm) is a **fungal infection** of the skin, hair, or nails. - It is typically treated with **antifungal medications** (e.g., azoles, terbinafine), not ivermectin. *Tuberculosis* - **Tuberculosis** is a bacterial infection caused by **Mycobacterium tuberculosis**, primarily affecting the lungs. - Treatment involves a multi-drug regimen of **antibiotics** (e.g., rifampin, isoniazid), for several months. *Syphilis* - **Syphilis** is a sexually transmitted bacterial infection caused by **Treponema pallidum**. - The primary treatment for syphilis is **penicillin**, usually administered via injection.

Question 1367: A 25-year-old female has been diagnosed to be suffering from tuberculosis categorized as category II (sputum +ve) case of relapse. According to the previous RNTCP (Revised National Tuberculosis Control Programme) guidelines, the treatment regimen recommended under DOTS was:

A. 3(HRZE)3 + 2(HRE)3 + 4(HR)3
B. 2(HRSZE)3 + 1(HRZE)3 + 5(HRE)3 (Correct Answer)
C. 3(HRSZE)3 + 1(HRZE)3 + 6(HRE)3
D. 2(HRZE)3 + 5(HR)3

Explanation: ***2(HRSZE)3 + 1(HRZE)3 + 5(HRE)3*** - This regimen reflects the standard **Category II DOTS regimen** under the **previous RNTCP guidelines** for **sputum-positive relapse cases**, which was an 8-month treatment protocol. - The intensive phase consisted of **2 months of daily Streptomycin, Isoniazid, Rifampicin, Pyrazinamide, and Ethambutol (HRSZE)**, followed by **1 month of daily Isoniazid, Rifampicin, Pyrazinamide, and Ethambutol (HRZE)**, and a continuation phase of **5 months of Isoniazid, Rifampicin, and Ethambutol (HRE)** given three times weekly. - **Note:** Under current NTEP (National TB Elimination Programme) guidelines, previously treated cases undergo drug susceptibility testing, and fixed Category II regimens are no longer the standard approach. *3(HRZE)3 + 2(HRE)3 + 4(HR)3* - This is an incorrect combination of drugs and durations that does not match any standard DOTS category under previous RNTCP guidelines. - Category II relapse cases required a five-drug intensive phase including Streptomycin, not a four-drug regimen. *3(HRSZE)3 + 1(HRZE)3 + 6(HRE)3* - While this option includes the correct five-drug intensive phase, the duration is incorrect—the intensive phase with Streptomycin should be **2 months, not 3 months**. - The continuation phase of 6 months (instead of 5 months) also makes the total treatment duration longer than the standard 8-month Category II protocol. *2(HRZE)3 + 5(HR)3* - This regimen represents the **Category I (new cases) regimen** under previous RNTCP guidelines, which used only four drugs in the intensive phase. - It **lacks Streptomycin**, which was essential for Category II (relapse/failure/treatment after default) cases, and the continuation phase lacks Ethambutol, which was included in Category II continuation.

Question 1368: Contact lens staining occurs in which ATT drug?

A. Rifampicin (Correct Answer)
B. INH
C. Thioacetazone
D. Pyrazinamide

Explanation: ***Rifampicin*** - **Rifampicin** causes **red-orange discoloration** of bodily fluids, including tears. - This discoloration can **permanently stain soft contact lenses**, making this an important patient counseling point. *INH (Isoniazid)* - **INH** is primarily associated with **hepatotoxicity** and **peripheral neuropathy** due to pyridoxine deficiency. - It does not cause significant discoloration of bodily fluids or contact lens staining. *Pyrazinamide* - **Pyrazinamide** is known for causing **hyperuricemia** and **hepatotoxicity**. - It does not lead to discoloration of bodily fluids or contact lenses. *Thioacetazone* - **Thioacetazone** (not a first-line ATT drug) is associated with severe **cutaneous hypersensitivity reactions**, including Stevens-Johnson syndrome. - It does not cause the characteristic discoloration or contact lens staining seen with rifampicin.

Question 1369: Minimum TB resistance is seen with which drug?

A. Rifampicin
B. Streptomycin
C. Isoniazid
D. Ethambutol (Correct Answer)

Explanation: ***Ethambutol*** - Among the first-line anti-TB drugs, **Ethambutol** has the **lowest rates of resistance development** - Resistance to Ethambutol is **less common** than to other first-line drugs like Isoniazid or Rifampicin - This makes it a valuable component of TB treatment regimens, particularly in maintaining effectiveness of combination therapy - Ethambutol resistance does occur but is relatively uncommon compared to other first-line agents *Isoniazid* - **Isoniazid resistance** is very common, occurring in approximately 10-15% of TB cases globally - Resistance arises from mutations in genes like *katG* and *inhA*, affecting drug activation and target binding - Despite resistance concerns, it remains a cornerstone drug due to its high efficacy when susceptibility is present *Rifampicin* - **Rifampicin resistance** is less common than Isoniazid but still significant - **Rifampicin-resistant TB (RR-TB)** is a marker for multidrug-resistant TB (MDR-TB) and indicates more severe disease - Development of Rifampicin resistance necessitates longer treatment regimens with second-line drugs *Streptomycin* - Historically one of the first antibiotics used for TB, but **resistance developed relatively quickly and is now widespread** - Due to the **high prevalence of resistance**, Streptomycin is no longer considered a first-line drug in most treatment programs - Has the highest resistance rates among the options listed

Question 1370: Not True about Bedaquiline

A. Inhibits mycobacterial ATP synthase
B. Contraindicated in pregnancy (Correct Answer)
C. Given in > 10 years aged patients
D. Given for MDR-TB patients

Explanation: ***Contraindicated in pregnancy*** - While bedaquiline's safety in pregnancy is not fully established, it is generally **not absolutely contraindicated** if the potential benefits outweigh the risks, especially in cases of MDR-TB. - Current guidelines suggest that it can be used with caution, and a woman taking bedaquiline should use **effective contraception** throughout treatment. *Inhibits mycobacterial ATP synthase* - This statement is **true**. Bedaquiline specifically targets the **F0F1-ATP synthase enzyme** in *Mycobacterium tuberculosis*. - By inhibiting this enzyme, bedaquiline disrupts the **energy production** pathway of the bacteria, leading to bacterial death. *Given in > 10 years aged patients* - This statement is **true**. Bedaquiline is approved for use in patients with **multidrug-resistant tuberculosis (MDR-TB)** who are **12 years of age and older**. - Its use in younger children is still under investigation, though some compassionate use cases exist. *Given for MDR-TB patients* - This statement is **true**. Bedaquiline is a key drug in the treatment of **multidrug-resistant tuberculosis (MDR-TB)** and **extensively drug-resistant tuberculosis (XDR-TB)**. - It is often used as part of a **combination regimen** to overcome drug resistance to first-line agents.

Practice by Chapter

Beta-Lactam Antibiotics

Practice Questions

Aminoglycosides

Practice Questions

Macrolides and Ketolides

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Tetracyclines

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Quinolones

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Sulfonamides and Trimethoprim

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Antimycobacterial Drugs

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Antifungal Agents

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Antiviral Drugs

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Antiparasitic Agents

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Principles of Antimicrobial Selection

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Antimicrobial Resistance

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