Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1561: Which of the following is not used as treatment for lymphatic filariasis -

A. DEC
B. Albendazole
C. Ivermectin
D. Praziquantel (Correct Answer)

Explanation: ***Praziquantel*** - **Praziquantel** is primarily an **anthelmintic drug** effective against **schistosomiasis** and **tapeworm infections**. - It does not have a significant role in the treatment of **lymphatic filariasis**. *Ivermectin* - **Ivermectin** is one of the **mainstays** of treatment for **lymphatic filariasis**, particularly in combination therapies. - It works by paralyzing and killing **microfilariae**, reducing their numbers in the bloodstream. *DEC* - **Diethylcarbamazine (DEC)** is a **highly effective antifilarial drug** used to kill both **microfilariae** and **adult worms** in lymphatic filariasis. - It is often used in mass drug administration programs and for individual treatment. *Albendazole* - **Albendazole** is an **anthelmintic drug** often used in combination with **Ivermectin** or **DEC** for the treatment of **lymphatic filariasis**. - It helps to kill **microfilariae** and has some macrofilaricidal effects, reducing the viability of adult worms.

Question 1562: What is the primary reason for using a combination of four drugs in Anti-Koch's Treatment (AKT) for tuberculosis?

A. To decrease the risk of resistance due to mutation. (Correct Answer)
B. To decrease the risk of resistance due to conjugation.
C. To enhance overall treatment efficacy.
D. To simplify treatment.

Explanation: ***To decrease the risk of resistance due to mutation*** - **Tuberculosis bacteria** can spontaneously develop resistance to a single drug through **random genetic mutations**. - Using multiple drugs simultaneously significantly reduces the probability that a bacterium will spontaneously develop resistance to **all drugs** in the regimen. - This is the **primary rationale** for multi-drug therapy in TB, as emphasized by WHO guidelines. *To decrease the risk of resistance due to conjugation* - **Conjugation** is a mechanism of horizontal gene transfer in bacteria, primarily involving the transfer of plasmids. - While important for antibiotic resistance in some bacteria, it is **not the primary mechanism** of resistance development in *Mycobacterium tuberculosis*. - TB resistance develops mainly through **chromosomal mutations**, not plasmid transfer. *To enhance overall treatment efficacy* - While multi-drug regimens do enhance treatment efficacy by targeting different bacterial populations (actively dividing, slow-growing, dormant), this is a **consequence** of the multi-drug approach. - The **primary reason** for using four drugs specifically is to prevent the emergence of **drug-resistant mutants**. - Enhanced efficacy is achieved *because* resistance is prevented, making this a secondary benefit. *To simplify treatment* - A four-drug regimen actually makes treatment more **complex** due to multiple pills, potential drug interactions, and increased side effects. - The complexity is a necessary trade-off for **resistance prevention** and treatment success.

Question 1563: Which sulphonamide has the longest acting duration?

A. Sulfadiazine
B. Sulphadoxine (Correct Answer)
C. Sulfamethoxazole
D. Sulfamethiazole

Explanation: ***Sulphadoxine*** - **Sulphadoxine** is known for its **exceptionally long elimination half-life**, which is due to its high plasma protein binding and slow renal excretion. - This property allows for **once-weekly dosing**, making it one of the longest-acting sulfonamides, often used in combinations for malaria prophylaxis or treatment. *Sulfadiazine* - **Sulfadiazine** has an intermediate half-life, typically requiring **multiple daily doses**. - It is commonly used for infections like **toxoplasmosis** and **nocardiosis**. *Sulfamethoxazole* - **Sulfamethoxazole** has an intermediate half-life, usually requiring **twice-daily administration**. - It is most famously co-formulated with **trimethoprim** (as co-trimoxazole) for a broad range of bacterial infections. *Sulfamethiazole* - **Sulfamethiazole** is a **short-acting sulfanilamide derivative** with a rapid elimination, meaning it would require frequent dosing. - It is not commonly used systemically due to its short duration of action.

Question 1564: Which of the following drugs is not used for prophylaxis against malaria?

A. Doxycycline
B. Artesunate (Correct Answer)
C. Mefloquine
D. Chloroquine

Explanation: Artesunate - **Artesunate** is a **fast-acting artemisinin derivative primarily used for treating acute malaria infections, especially severe or complicated cases**, and is not recommended for prophylaxis [4]. - Its short half-life and rapid clearance make it unsuitable for preventing malaria, as it would require frequent dosing, which is impractical for long-term prevention. *Doxycycline* - **Doxycycline** is an **antibiotic** that can be used for malaria prophylaxis, particularly in areas with **chloroquine-resistant P. falciparum** [1]. - It works by inhibiting protein synthesis in the parasite and must be taken daily, starting before travel and continuing for a period after returning [1]. *Chloroquine* - **Chloroquine** was historically a cornerstone for malaria prophylaxis due to its effectiveness and low cost, particularly in areas with **sensitive Plasmodium species.** [2] - However, widespread **chloroquine resistance**, especially in **P. falciparum**, has limited its current use for prophylaxis to specific regions where resistance is not prevalent [2]. *Mefloquine* - **Mefloquine** is an **antimalarial drug** commonly used for prophylaxis, especially in areas with **chloroquine-resistant P. falciparum** [2], [3]. - It is known for its convenience of once-weekly dosing but can have significant **neuropsychiatric side effects**, limiting its use in some individuals [3].

Question 1565: What is the primary purpose of administering a multidrug regimen for tuberculosis (TB) treatment?

A. To prevent the development of drug resistance (Correct Answer)
B. To provide broad-spectrum coverage
C. To minimize side effects
D. To ensure treatment adherence

Explanation: ***To prevent the development of drug resistance*** - Using multiple drugs simultaneously targets different bacterial pathways, reducing the likelihood of *Mycobacterium tuberculosis* evolving resistance to any single drug [1] - This strategy ensures that even if a few bacteria are naturally resistant to one drug, other drugs in the regimen will eliminate them [1] - This is the fundamental principle behind multidrug TB therapy as per WHO guidelines *To provide broad-spectrum coverage* - TB treatment uses multiple drugs specifically against *Mycobacterium tuberculosis*, not for broad-spectrum coverage [2] - These regimens are tailored to the known characteristics of TB bacteria, not to cover a wide range of pathogens [2] - The drugs used (rifampicin, isoniazid, pyrazinamide, ethambutol) are relatively specific for mycobacteria [2] *To minimize side effects* - Administering multiple anti-TB drugs actually increases the risk of cumulative side effects due to drug interactions and individual toxicities [3] - Each drug has its own toxicity profile (hepatotoxicity, optic neuritis, hyperuricemia) [3] - While side effects are monitored, minimizing them is not the primary reason for multidrug approach *To ensure treatment adherence* - Treatment adherence refers to the patient's consistent use of prescribed medications, not the number of drugs - A complex multidrug regimen can actually make adherence more challenging - Directly Observed Therapy (DOT) is often needed to improve adherence with multidrug regimens

Question 1566: In a child admitted with Haemophilus influenzae meningitis, cefotaxime was started instead of ampicillin. Which of the following is the likely reason for this?

A. It is cheap
B. H. influenzae strains known to produce Beta lactamase (Correct Answer)
C. Easier to give
D. H. influenzae strains known to have altered penicillin binding protein

Explanation: ***H. influenzae strains known to produce Beta lactamase*** - Many *H. influenzae* strains, particularly in meningitis, produce **beta-lactamase enzymes** that inactivate ampicillin. - **Cefotaxime**, a third-generation cephalosporin, is **stable against beta-lactamases**, making it an effective empirical treatment. *Easier to give* - The route and ease of administration are generally **not the primary factors** in choosing between ampicillin and cefotaxime in a severe infection like meningitis. - Both medications can be administered intravenously, which is standard for meningitis treatment. *It is cheap* - While cost is a consideration in healthcare, **efficacy and clinical outcome** for a life-threatening condition like meningitis take precedence over cost. - Treatment choices are primarily driven by **antimicrobial susceptibility patterns** and patient safety. *H. influenzae strains known to have altered penicillin binding protein* - While **altered penicillin-binding proteins (PBPs)** can lead to resistance in some bacteria (e.g., *Streptococcus pneumoniae*), it is **not the predominant mechanism of resistance** to ampicillin in *H. influenzae*. - **Beta-lactamase production** is the much more common and significant reason for ampicillin resistance in *H. influenzae*.

Question 1567: What is the recommended duration of erythromycin for the treatment of diphtheria?

A. 3 days
B. 7 days
C. 14 days (Correct Answer)
D. 30 days

Explanation: ***14 days*** - The recommended duration for **erythromycin** in treating diphtheria is **14 days** to ensure eradication of *Corynebacterium diphtheriae* and prevent toxin production. - This duration helps to eliminate the carrier state and reduce the risk of transmission to others. *3 days* - A 3-day course of antibiotics is **insufficient** for the complete eradication of *Corynebacterium diphtheriae* in diphtheria. - Such a short duration would likely lead to **treatment failure** and persistence of the infection. *7 days* - While 7 days is a common antibiotic duration for some infections, it is generally considered **too short** for diphtheria treatment. - A 7-day course may not fully eliminate the bacteria, potentially leading to **relapse** or a prolonged carrier state. *30 days* - A 30-day course of erythromycin for diphtheria is **unnecessarily long** and could increase the risk of side effects and antibiotic resistance. - The goal is eradication without excessive drug exposure, which 14 days achieves effectively.

Question 1568: On chronic use, linezolid leads to which of the following?

A. Thrombocytopenia (Correct Answer)
B. Deranged LFT
C. Nephrotoxicity
D. Ototoxicity

Explanation: ***Thrombocytopenia*** - **Linezolid** is known to cause **myelosuppression**, particularly **thrombocytopenia**, with prolonged use (typically >2 weeks). - This adverse effect is usually **reversible** upon discontinuation of the drug. - This is the **most characteristic** and **dose-limiting** hematologic toxicity of chronic linezolid therapy. *Deranged LFT* - While **linezolid** can occasionally cause **elevated liver enzymes**, this is a **less common** adverse effect compared to myelosuppression. - **Thrombocytopenia** is far more characteristic of **chronic linezolid use** and is the primary concern requiring monitoring. - Hepatotoxicity with linezolid is typically mild and less dose-limiting than hematologic effects. *Nephrotoxicity* - **Linezolid** is generally considered to have a low risk of **nephrotoxicity** and does not typically cause significant kidney damage. - **Aminoglycosides** or **vancomycin** are examples of antibiotics more commonly associated with nephrotoxic effects. *Ototoxicity* - **Ototoxicity**, characterized by hearing loss or tinnitus, is not a common or recognized side effect of **linezolid** therapy. - This adverse effect is more frequently associated with drugs like **aminoglycosides** or high-dose **loop diuretics**.

Question 1569: Which of the following antimalarials is a slow-acting schizonticide?

A. Artemether
B. Mefloquine
C. Pyrimethamine (Correct Answer)
D. Quinine

Explanation: ***Pyrimethamine***- Pyrimethamine is a **folate antagonist** [1, 2] that acts as a **slow-acting schizonticide** [1, 3], primarily inhibiting dihydrofolate reductase in the parasite [1].- Due to its slow onset [1], it is typically used in combination with other faster-acting antimalarials, such as sulfadoxine, for treatment or prophylaxis [1].*Artemether*- Artemether is an **artemisinin derivative**, known for its **rapid action** and potent effect against all erythrocytic stages of *Plasmodium falciparum*.- It is a **fast-acting schizonticide** that causes widespread damage to parasite membranes and proteins.*Mefloquine*- Mefloquine is an antimalarial drug recognized for its **long half-life** and efficacy against multidrug-resistant *Plasmodium falciparum*.- While effective, it is considered of **intermediate speed** compared to the rapid action of artemisinins or the very slow action of drugs like pyrimethamine.*Quinine*- Quinine is a **fast-acting schizonticide** that is effective against the asexual erythrocytic forms of *Plasmodium* parasites.- Although potent, its use is limited by potential adverse effects such as **cinchonism** and a short half-life requiring frequent dosing.

Question 1570: Anaerobic bacteria are intrinsically resistant to which of the following antibiotics?

A. Beta-lactams (e.g., penicillin)
B. Aminoglycosides (e.g., gentamicin) (Correct Answer)
C. Chloramphenicol (broad-spectrum antibiotic)
D. Metronidazole (used for anaerobic infections)

Explanation: ***Aminoglycosides (e.g., gentamicin)*** - Anaerobic bacteria lack the **oxygen-dependent transport systems** necessary to take up aminoglycosides into the bacterial cell. - This results in **intrinsic resistance** because the drug cannot reach its intracellular ribosomal target. *Beta-lactams (e.g., penicillin)* - While some anaerobes (like certain *Bacteroides* species) can be resistant to specific beta-lactams due to **beta-lactamase production**, it's not an intrinsic resistance across all anaerobes to all beta-lactams. - Many anaerobes are **susceptible to penicillin**, especially those that do not produce beta-lactamase, or to beta-lactamase inhibitors combination drugs. *Chloramphenicol (broad-spectrum antibiotic)* - Chloramphenicol is effective against many anaerobic bacteria by inhibiting **protein synthesis**. - Anaerobes are generally **susceptible** to chloramphenicol, and it is not an antibiotic to which they are intrinsically resistant. *Metronidazole (used for anaerobic infections)* - Metronidazole is a **prodrug** that requires anaerobic conditions to become activated. - It is highly effective against most obligate anaerobes and is a common choice for treating **anaerobic infections**, indicating susceptibility, not intrinsic 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

Practice Questions

Principles of Antimicrobial Selection

Practice Questions

Antimicrobial Resistance

Practice Questions

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