Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1391: Leprosy is made non-infectious by Rifampicin in:

A. 3 weeks
B. 2 weeks (Correct Answer)
C. 4 weeks
D. 1 week

Explanation: ***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.

Question 1392: Griseofulvin is used in –

A. P. versicolor
B. Candidiasis
C. Tinea capitis (Correct Answer)
D. All of the options

Explanation: ***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.

Question 1393: The duration of treatment with rifampicin by which a leprosy patient becomes non-infective is:

A. 1 month
B. 72 hours (Correct Answer)
C. 2 weeks
D. 1 week

Explanation: **72 hours** - **Rifampicin** rapidly kills *Mycobacterium leprae* and significantly reduces bacterial viability, making the patient **non-infective** within a few days of treatment initiation. - This quick action of rifampicin is crucial for preventing further transmission of leprosy. *1 month* - While treatment for leprosy often extends for several months or years, the patient typically becomes **non-infectious much earlier**, specifically within the first few days, due to the rapid bactericidal effect of rifampicin. - A one-month duration refers more to the follow-up or continued treatment phase rather than the time to achieve non-infectivity. *2 weeks* - This duration is longer than necessary to achieve non-infectivity with rifampicin. The rapid action of **rifampicin** means the patient is no longer infectious within approximately **72 hours**. - Two weeks of treatment would further reduce the bacterial load but is not the minimum time for non-infectivity. *1 week* - While closer to the correct answer than 1 month or 2 weeks, **1 week** is still an overestimate for the time it takes for a leprosy patient to become non-infective with rifampicin therapy. - Significant reduction in contagiousness occurs much faster, typically within **72 hours**.

Question 1394: Which of the following is true about Mafenide?

A. Can penetrate eschars
B. May cause metabolic acidosis (Correct Answer)
C. Can be used orally
D. Doesn't cause burning sensation when applied to raw surface

Explanation: ***May cause metabolic acidosis*** - Mafenide acetate is a **carbonic anhydrase inhibitor**, which can disrupt the kidney's ability to excrete acid. - This leads to an accumulation of hydrogen ions in the body, resulting in **metabolic acidosis**. - This is an **important adverse effect** that requires monitoring in burn patients. *Can penetrate eschars* - **This statement is actually TRUE** - Mafenide acetate has excellent eschar penetration, which is one of its key advantages over silver sulfadiazine. - However, the metabolic acidosis is more commonly emphasized as a distinguishing adverse effect in exams. - Both statements are medically accurate, but metabolic acidosis is the more clinically significant feature to remember. *Can be used orally* - **Mafenide acetate** is a topical agent specifically designed for application to burn wounds. - It is **not formulated for oral administration** and would cause systemic toxicity if used in that manner. *Doesn't cause burning sensation when applied to raw surface* - Mafenide acetate is well-known for causing a **significant burning sensation and pain** when applied to burn wounds. - This local discomfort can be a major challenge for patient compliance and pain management.

Question 1395: Treatment of choice for chloroquine resistant malaria is :

A. Chloroquine
B. Primaquine
C. Quinine
D. Artemisinin-based combination therapies (ACTs) (Correct Answer)

Explanation: ***Artemisinin-based combination therapies (ACTs)*** - **ACTs** are the recommended first-line treatment for **uncomplicated Plasmodium falciparum malaria**, especially in areas with chloroquine resistance, due to their high efficacy and rapid action. - They combine an **artemisinin derivative** (which rapidly reduces parasite biomass) with a longer-acting partner drug (which provides sustained curative effect and prevents recrudescence), addressing resistance mechanisms. *Chloroquine* - **Chloroquine** is the treatment of choice for **chloroquine-sensitive malaria**, but it is ineffective against resistant strains. - Its widespread use led to the development of **drug resistance** in many regions, particularly for *Plasmodium falciparum*. *Primaquine* - **Primaquine** is primarily used for **radical cure** to prevent relapses in *Plasmodium vivax* and *Plasmodium ovale* malaria by targeting hypnozoites in the liver. - It is **not effective** as a sole agent for treating acute *Plasmodium falciparum* infections, particularly chloroquine-resistant ones. *Quinine* - **Quinine** has historically been used for treating malaria, including some resistant strains, but is now typically reserved for **severe malaria** or in specific combination regimens where ACTs are unavailable. - Its use can be associated with side effects such as **cinchonism** (tinnitus, headache, nausea) and a longer treatment course compared to ACTs.

Question 1396: What is false about mafenide acetate?

A. Deeper penetration
B. Painful
C. Metabolic acidosis
D. Immunomodulatory action (Correct Answer)

Explanation: ***Immunomodulatory action*** - Mafenide acetate is an **antimicrobial agent** primarily used topically for burn wound infections due to its broad spectrum of activity against Gram-positive and Gram-negative bacteria. - Its mechanism of action involves **inhibiting bacterial carbonic anhydrase** and folic acid synthesis, and it does not possess significant immunomodulatory properties. *Deeper penetration* - Mafenide acetate has a **low molecular weight** and is readily absorbed through eschar, allowing for **deeper penetration** into burn wounds compared to other topical agents. - This characteristic makes it effective in treating established burn wound infections but also contributes to its systemic absorption and potential side effects. *Painful* - Application of mafenide acetate can be **very painful** for patients due to its chemical composition and the disruption of nerve endings in burn wounds. - This significant side effect leads to patient discomfort and may necessitate pre-medication or alternative pain management strategies. *Metabolic acidosis* - Mafenide acetate is an inhibitor of **carbonic anhydrase**, which is crucial for acid-base balance, particularly in the kidneys. - Systemic absorption can lead to **metabolic acidosis** due to impaired bicarbonate reabsorption and increased acid excretion, requiring careful monitoring of electrolyte levels, especially in patients with large burn areas or renal dysfunction.

Question 1397: Cetrimide is

A. Halogen
B. Aldehyde
C. Phenol
D. Quaternary ammonium compounds (Correct Answer)

Explanation: ***Quaternary ammonium compounds*** - Cetrimide is a **cationic surfactant** belonging to the class of **quaternary ammonium compounds**. - Its mechanism of action involves disrupting microbial cell membranes, leading to **cell leakage** and death, making it effective as an antiseptic. *Halogen* - Halogens (e.g., **iodine, chlorine**) exert antimicrobial effects through **oxidation** and halogenation of microbial cellular components. - While effective, their chemical structure and mechanism are distinct from that of cetrimide. *Aldehyde* - Aldehydes (e.g., **formaldehyde, glutaraldehyde**) act by **alkylating** proteins and nucleic acids, leading to broad-spectrum antimicrobial activity. - This class of disinfectants has a different chemical structure and mode of action compared to cetrimide. *Phenol* - Phenols (e.g., **phenol, cresol**) denature proteins and disrupt cell membranes, and are characterized by a **hydroxyl group** attached to an aromatic ring. - Cetrimide does not possess the phenolic chemical structure or its associated mechanism of action.

Question 1398: Which of the following are the core components present in all acellular pertussis vaccines?

A. Pertactin, filamentous hemagglutinin, cytotoxin, endotoxin
B. Pertactin, filamentous hemagglutinin, fimbriae, endotoxin
C. Filamentous hemagglutinin, pertussis toxin, fimbriae, pertactin
D. Pertactin, pertussis toxin, filamentous hemagglutinin (Correct Answer)

Explanation: ***Correct: Pertactin, pertussis toxin, filamentous hemagglutinin*** - The **acellular pertussis vaccine (DTaP/Tdap)** contains purified components of *Bordetella pertussis* to elicit immunity without causing disease - The **three core components** present in ALL acellular pertussis vaccine formulations are: - **Pertussis toxoid (PT)** - inactivated pertussis toxin, critical for neutralizing the main virulence factor - **Filamentous hemagglutinin (FHA)** - adhesion protein essential for bacterial attachment - **Pertactin (PRN)** - outer membrane protein important for adhesion and immune response - These components are immunogenic and necessary for protective immunity while minimizing adverse reactions *Incorrect: Pertactin, filamentous hemagglutinin, cytotoxin, endotoxin* - While **pertactin** and **filamentous hemagglutinin** are correct, "cytotoxin" is too vague (likely refers to pertussis toxin which should be named specifically) - **Endotoxin** (lipopolysaccharide) is intentionally excluded from acellular vaccines due to its high reactogenicity and pro-inflammatory effects *Incorrect: Pertactin, filamentous hemagglutinin, fimbriae, endotoxin* - **Pertactin** and **filamentous hemagglutinin** are correct core components - While **fimbriae (types 2 and 3)** are included in some vaccine formulations (3-component vs 5-component vaccines), they are not present in ALL formulations - **Endotoxin** is excluded due to reactogenicity *Incorrect: Filamentous hemagglutinin, pertussis toxin, fimbriae, pertactin* - This option includes all three core components correctly - However, **fimbriae** are additional components in some enhanced formulations (5-component vaccines) but not universally present in all acellular pertussis vaccines (3-component vaccines contain only PT, FHA, and PRN) - Since the question asks for components in ALL vaccines, fimbriae cannot be included

Question 1399: Which of the following is NOT a criterion for defining extensively drug-resistant tuberculosis (XDR-TB)?

A. Isoniazid + Rifampicin + Fluoroquinolone
B. Isoniazid + Rifampicin + Ethambutol + Fluoroquinolone
C. Fluoroquinolone (Correct Answer)
D. Isoniazid + Rifampicin + Kanamycin

Explanation: ***Fluoroquinolone*** - Resistance to **fluoroquinolone alone** is NOT a criterion for XDR-TB because XDR-TB requires a **baseline of MDR-TB** (resistance to both rifampicin and isoniazid) plus additional resistances. - XDR-TB definition (WHO 2021): **MDR-TB** + resistance to **any fluoroquinolone** + resistance to **at least one Group A drug** (bedaquiline or linezolid). - Fluoroquinolone resistance in isolation does not meet any of these combined criteria. *Isoniazid + Rifampicin + Fluoroquinolone* - This represents **MDR-TB** (rifampicin + isoniazid resistance) plus **fluoroquinolone resistance**. - This is a partial criterion approaching XDR-TB but still requires additional resistance to at least one Group A drug (bedaquiline or linezolid) for complete XDR-TB classification. - However, this combination includes the essential MDR-TB base and fluoroquinolone component. *Isoniazid + Rifampicin + Ethambutol + Fluoroquinolone* - This includes **MDR-TB** (rifampicin + isoniazid), **fluoroquinolone resistance**, and ethambutol (first-line drug). - While ethambutol resistance alone doesn't define XDR-TB, this combination includes the critical MDR-TB and fluoroquinolone components required for XDR-TB classification. - Similar to above, would need Group A drug resistance for complete XDR-TB. *Isoniazid + Rifampicin + Kanamycin* - This represents **MDR-TB** plus resistance to **kanamycin** (a second-line injectable). - Under previous WHO definitions (pre-2021), injectable resistance was part of XDR-TB criteria. - This combination includes the MDR-TB base essential for any XDR-TB classification, though it lacks fluoroquinolone resistance.

Question 1400: What is the treatment for single lesion leprosy?

A. Dapsone and rifampicin
B. Rifampicin, ofloxacin, and minocycline (Correct Answer)
C. Rifampicin, ofloxacin, and dapsone
D. Dapsone, clofazimine, and ofloxacin

Explanation: ***Rifampicin, ofloxacin, and minocycline*** - This combination is the recommended **single-dose multidrug therapy (SDMDT)** for **single lesion paucibacillary leprosy**, which is classified as *single-lesion tuberculoid leprosy*. - Administered as a single, supervised dose, this regimen aims to simplify treatment and improve compliance for this specific presentation. *Dapsone and rifampicin* - This is the traditional regimen for **paucibacillary leprosy**, but it is typically given over **6 months**, not as a single dose for a single lesion. - It lacks the additional agents that provide the efficacy for a single-dose treatment in specific cases. *Rifampicin, ofloxacin, and dapsone* - While dapsone is part of standard multidrug therapy, it is not used in combination with ofloxacin and minocycline for **single-lesion leprosy** as a single dose. - This specific combination is not a recognized or recommended regimen for any type of leprosy. *Dapsone, clofazimine, and ofloxacin* - **Dapsone** and **clofazimine** are components of the **multibacillary leprosy** regimen, typically given with rifampicin for a longer duration (12 months). - Ofloxacin is not typically combined with dapsone and clofazimine in standard regimens for either paucibacillary or multibacillary leprosy.

Practice by Chapter

Beta-Lactam Antibiotics

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Aminoglycosides

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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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