Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1541: Drug for prophylaxis of malaria in chloroquine resistant P.falciparum ?

A. Mefloquine (Correct Answer)
B. Quinine
C. Halofantrine
D. Artesunate

Explanation: ***Mefloquine*** - **Mefloquine** is a well-established and effective drug for prophylaxis against **chloroquine-resistant Plasmodium falciparum**. - It is often used in regions with high chloroquine resistance, although it can have significant neuropsychiatric side effects. *Quinine* - **Quinine** is primarily used for the *treatment* of severe or complicated malaria, especially in cases of multidrug resistance. - It is not typically recommended for malaria **prophylaxis** due to its relatively short half-life and potential for side effects with chronic use. *Halofantrine* - **Halofantrine** is an *antimalarial treatment* drug, not a prophylactic agent. - Its use is limited due to potential for **cardiotoxicity** (QT prolongation) and poor bioavailability. *Artesunate* - **Artesunate** is an **artemisinin derivative** and a potent antimalarial drug used for the *treatment* of acute malaria, particularly severe cases. - It has a very short half-life and is not suitable for **prophylaxis**.

Question 1542: Which of the following is a topical sulfonamide ?

A. Sulfadoxine
B. Sulfamethopyrazine
C. Sulfisoxazole
D. Mafenide (Correct Answer)

Explanation: ***Mafenide*** - **Mafenide** is a **sulfonamide antibiotic** primarily used **topically** as a cream for preventing and treating **wound infections**, particularly in **burn patients**. - It works by inhibiting bacterial growth and has good penetrative capabilities in **necrotic tissue** and **eschar**. - It is **water-soluble** and can penetrate burn eschar effectively. *Sulfadoxine* - **Sulfadoxine** is a **long-acting oral sulfonamide** frequently used in combination with **pyrimethamine** for conditions like **malaria** and **toxoplasmosis**. - It is administered **systemically**, not topically. *Sulfamethopyrazine* - **Sulfamethopyrazine** (also known as sulfalene) is another **long-acting sulfonamide** primarily used **orally** for conditions such as **malaria** and **urinary tract infections**. - Its clinical application is **systemic**, not topical. *Sulfisoxazole* - **Sulfisoxazole** is a **short-acting oral sulfonamide** used systemically for **urinary tract infections** and other bacterial infections. - It is **rapidly absorbed** and excreted, making it suitable for systemic use, not topical application.

Question 1543: An Englishman travels to a place which is resistant to chloroquine and mefloquine. What should he take as prophylaxis?

A. Primaquine
B. Atovaquone-proguanil (Correct Answer)
C. Doxycycline
D. Proguanil

Explanation: ***Atovaquone-proguanil*** - This combination, known as **Malarone**, is the most appropriate prophylactic agent for areas with **multi-drug resistant malaria**, including resistance to chloroquine and mefloquine [1], [2]. - It targets multiple stages of the parasite life cycle, providing excellent protection and is generally well-tolerated with specific **WHO and CDC recommendations** for chloroquine and mefloquine resistant areas [1], [3]. *Primaquine* - **Primaquine** is primarily used for **causal prophylaxis** against *P. vivax* and *P. ovale* to prevent relapse, not as primary prophylaxis [2]. - It is not typically recommended as the primary prophylactic agent in areas with **chloroquine and mefloquine resistance** and requires **G6PD testing** due to risk of hemolysis [1]. *Proguanil* - While proguanil is used for malaria prophylaxis, **proguanil alone** is not effective enough for prophylaxis in areas with multi-drug resistant malaria. - It is typically used in **combination with atovaquone** rather than as monotherapy for effective protection [3]. *Doxycycline* - **Doxycycline** is also an effective prophylactic agent for areas with **chloroquine and mefloquine-resistant malaria** and is commonly recommended [1], [2]. - While effective, it can cause **photosensitivity** and **gastrointestinal upset**, making atovaquone-proguanil the preferred first-line choice.

Question 1544: What is the mechanism of action of aminoglycoside antibiotics?

A. Inhibition of protein synthesis (Correct Answer)
B. Inhibition of DNA replication
C. Disruption of the cell membrane
D. Inhibition of bacterial cell wall synthesis

Explanation: ***Inhibition of protein synthesis*** - Aminoglycosides **bind irreversibly to the 30S ribosomal subunit** of bacteria, interfering with the initiation complex formation and causing misreading of mRNA. - This leads to the production of **non-functional proteins** and ultimately bacterial cell death, making them bactericidal. *Disruption of the cell membrane* - This mechanism is characteristic of **polymyxins** (e.g., colistin), which interact with bacterial cell membranes, increasing permeability and causing leakage of intracellular contents. - Aminoglycosides do not primarily target the cell membrane for their bactericidal action. *Inhibition of DNA replication* - This mechanism is associated with **fluoroquinolones**, which inhibit bacterial topoisomerase II (DNA gyrase) and topoisomerase IV. - Aminoglycosides do not interfere with DNA synthesis or replication. *Inhibition of bacterial cell wall synthesis* - This is the mechanism of action for **beta-lactam antibiotics** (e.g., penicillins, cephalosporins) and **glycopeptides** (e.g., vancomycin), which target peptidoglycan synthesis. - Aminoglycosides do not affect the bacterial cell wall but rather their intracellular protein machinery.

Question 1545: Which of the following is NOT an advantage of amoxicillin over ampicillin?

A. Spectrum includes H. influenzae & Shigella (Correct Answer)
B. Incidence of diarrhea is lower
C. Food does not interfere with its absorption
D. Better bioavailability & faster action

Explanation: ***Spectrum includes H. influenzae & Shigella*** - Amoxicillin and ampicillin both have a similar spectrum of activity against *Haemophilus influenzae* and *Shigella* species. Neither drug possesses a distinct advantage over the other in this regard for these specific pathogens. - Therefore, stating that amoxicillin's spectrum *includes* these bacteria as an advantage over ampicillin implies a unique characteristic, which is incorrect. *Better bioavailability & faster action* - **Amoxicillin** has superior oral **bioavailability** compared to ampicillin, leading to higher and more consistent blood levels. - This improved absorption often translates to a **faster onset of action** and allows for less frequent dosing. *Incidence of diarrhea is lower* - **Amoxicillin** is associated with a **lower incidence of diarrhea** and other gastrointestinal side effects compared to ampicillin. - This is partly due to its better absorption, meaning less unabsorbed drug reaches the colon to disrupt normal flora. *Food does not interfere with its absorption* - The absorption of **amoxicillin is largely unaffected by food**, allowing it to be taken without regard to meals. - In contrast, ampicillin's absorption can be significantly reduced when taken with food, making amoxicillin more convenient.

Question 1546: Which of the following conditions is not treated by penicillin G?

A. Bacterial meningitis
B. Syphilis
C. Anthrax
D. Rickettsial infection (Correct Answer)

Explanation: ***Rickettsial infection*** - **Rickettsial infections**, such as Rocky Mountain spotted fever or typhus, are caused by **obligate intracellular bacteria** that are not susceptible to penicillin G. - The primary treatment for rickettsial infections is **doxycycline**, due to its ability to penetrate host cells and inhibit bacterial protein synthesis. *Bacterial meningitis* - **Bacterial meningitis**, particularly caused by susceptible strains of *Neisseria meningitidis*, *Streptococcus pneumoniae*, and *Haemophilus influenzae*, can be effectively treated with **high-dose intravenous penicillin G** [1]. - Penicillin G's ability to cross the **blood-brain barrier** in inflamed meninges makes it a suitable option, though ceftriaxone is now more commonly used empirically due to resistance concerns [2]. *Syphilis* - **Penicillin G** remains the **drug of choice** for all stages of syphilis, caused by *Treponema pallidum*. - For primary, secondary, and early latent syphilis, a **single intramuscular dose of benzathine penicillin G** is curative. *Anthrax* - While **ciprofloxacin** and **doxycycline** are often considered first-line for anthrax, **penicillin G** can also be an effective treatment for susceptible strains of *Bacillus anthracis*. - It is particularly used in cases of less severe cutaneous anthrax or to de-escalate treatment once susceptibility is confirmed.

Question 1547: First generation cephalosporins are active against?

A. Gram negative bacteria
B. Gram positive bacteria (Correct Answer)
C. Anaerobes
D. Dermatophytes

Explanation: ***Gram positive bacteria*** - First-generation cephalosporins, such as **cefazolin** and **cephalexin**, primarily exhibit excellent activity against many **Gram-positive cocci**, including **staphylococci** and **streptococci**. - They are commonly used for skin and soft tissue infections and surgical prophylaxis due to this Gram-positive coverage. *Gram negative bacteria* - While first-generation cephalosporins have *some* activity against limited Gram-negative bacteria (e.g., *E. coli*, *Klebsiella pneumoniae*, *P. mirabilis*), their spectrum is generally weak and unreliable compared to later generations of cephalosporins. - They are not the drug of choice for serious Gram-negative infections. *Anaerobes* - First-generation cephalosporins have **poor activity** against most **anaerobic bacteria**. - For infections involving anaerobes, other antibiotics like **metronidazole**, **clindamycin**, or later-generation cephalosporins (e.g., cefoxitin, cefotetan) are generally preferred. *Dermatophytes* - Dermatophytes are **fungi** that cause skin, hair, and nail infections. - Cephalosporins are **antibacterial agents** and have **no activity** against fungi. Antifungal medications are required to treat dermatophyte infections.

Question 1548: Which drug is commonly used to treat chronic hepatitis B infection?

A. Zanamivir
B. Atazanavir
C. Abacavir
D. Entecavir (Correct Answer)

Explanation: ***Entecavir*** - **Entecavir** is an oral **nucleoside analog reverse transcriptase inhibitor** specifically approved and widely used for the treatment of **chronic hepatitis B virus (HBV) infection**. - It works by inhibiting HBV DNA polymerase, thereby reducing **viral replication** and preventing disease progression. *Atazanavir* - **Atazanavir** is a **protease inhibitor** primarily used in the treatment of **HIV infection**. - It is not indicated for the treatment of **hepatitis B virus infection**. *Zanamivir* - **Zanamivir** is a **neuraminidase inhibitor** used in the treatment and prevention of **influenza A and B viruses**. - It has no activity against **hepatitis B virus**. *Abacavir* - **Abacavir** is a **nucleoside reverse transcriptase inhibitor (NRTI)** used to treat **HIV infection**. - While it is an NRTI, it does not have significant efficacy against **hepatitis B virus** and is not used for its treatment.

Question 1549: Drug of choice for Pneumocystis jirovecii in pregnancy?

A. Primaquine
B. Dapsone
C. Pentamidine
D. Trimethoprim-sulfamethoxazole (SMZ/TMP) (Correct Answer)

Explanation: ***Trimethoprim-sulfamethoxazole (SMZ/TMP)*** - Despite being a **folate antagonist**, SMZ/TMP is considered safe and the **drug of choice** for treating **Pneumocystis jirovecii pneumonia (PJP)** in pregnant women, particularly as the benefits outweigh the risks. - It is recommended to supplement with **folic acid** during treatment to mitigate potential teratogenic risks, although these risks are generally low. *Primaquine* - **Primaquine** is primarily used for the treatment of **Plasmodium vivax** and **Plasmodium ovale malaria**, specifically targeting hypnozoites in the liver. - It is contraindicated in pregnancy due to the risk of **hemolytic anemia** in the fetus, especially if the fetus has **glucose-6-phosphate dehydrogenase (G6PD) deficiency**. *Dapsone* - **Dapsone** is used in the treatment of **leprosy**, **dermatitis herpetiformis**, and as an alternative for **PJP prophylaxis** in HIV-positive patients. - While it can be used for PJP prophylaxis, its efficacy for **active PJP treatment** is lower than SMZ/TMP, and it carries risks of **hemolytic anemia** and **methemoglobinemia**, particularly in pregnancy. *Pentamidine* - **Pentamidine** is an alternative treatment for **PJP**, especially in patients who cannot tolerate SMZ/TMP. - It is typically reserved for **severe cases** or as a second-line agent due to its potential for **significant toxicity**, including hypotension, nephrotoxicity, and hypoglycemia, which can be particularly concerning in pregnancy.

Question 1550: What is the drug of choice for listeria meningitis?

A. Ampicillin (Correct Answer)
B. Cefotaxime
C. Ciprofloxacin
D. Ceftriaxone

Explanation: ***Ampicillin*** - **Ampicillin** is the **drug of choice** for *Listeria monocytogenes* meningitis due to its excellent in vitro activity and good central nervous system penetration. - It is often used in combination with an **aminoglycoside** (e.g., gentamicin) for synergistic bactericidal activity, especially in severe cases, though gentamicin does not penetrate the CSF well. *Cefotaxime* - **Third-generation cephalosporins** like cefotaxime have poor activity against *Listeria monocytogenes* due to the organism's intrinsic resistance to these agents. - While effective against many other bacterial causes of meningitis (e.g., *S. pneumoniae*, *N. meningitidis*), it is not appropriate for *Listeria*. *Ceftriaxone* - Similar to cefotaxime, **ceftriaxone** is a third-generation cephalosporin and is **ineffective** against *Listeria monocytogenes* due to the lack of penicillin-binding protein (PBP) affinity. - Its use for *Listeria* meningitis would lead to treatment failure. *Ciprofloxacin* - **Ciprofloxacin**, a fluoroquinolone, is generally **not recommended** as a first-line treatment for *Listeria* meningitis, despite some in vitro activity. - Its use is typically reserved for patients with severe allergies to penicillins, and even then, **trimethoprim-sulfamethoxazole** is usually preferred as an alternative to ampicillin.

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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