Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1571: Which of the following is used in the prophylaxis of meningococcus?

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

Explanation: ***Rifampicin*** - **Rifampicin** is a recommended agent for **chemoprophylaxis** against **meningococcal disease**, especially for close contacts of patients. - It works by eliminating the carriage of *Neisseria meningitidis* in the **nasopharynx**. *Erythromycin* - **Erythromycin** is a **macrolide antibiotic** primarily used for respiratory tract infections and certain skin infections. - It is **not effective** for the prophylaxis of meningococcal disease due to poor penetration into the nasopharynx and varied efficacy against *N. meningitidis*. *Tetracycline* - **Tetracyclines** are broad-spectrum antibiotics, but they are **not typically used** for meningococcal prophylaxis. Resistance is common [1], and other agents are preferred due to better efficacy and lower risk of side effects in this context. *Penicillin* - **Penicillin** is effective for treating **active meningococcal infection** but is **not suitable for prophylaxis**. - It does not consistently eradicate the carrier state of *N. meningitidis* from the nasopharynx, which is essential for prophylaxis.

Question 1572: Why is a regimen of four drugs recommended for a TB patient on the first visit?

A. To prevent emergence of drug-resistant strains (Correct Answer)
B. To reduce bacterial load effectively
C. To minimize treatment duration
D. None of the options

Explanation: ***To prevent emergence of drug-resistant strains*** - Using a **four-drug regimen** at the initial stage significantly reduces the likelihood of **Mycobacterium tuberculosis** developing resistance to any single drug. - This strategy ensures that even if a small number of bacteria are naturally resistant to one drug, the other drugs will still be effective in killing them, preventing the proliferation of **resistant strains**. *To minimize treatment duration* - While a multi-drug regimen is effective, its primary goal is not to minimize treatment duration but rather to ensure **eradication of the infection** and prevent resistance. - Treatment duration is determined by the need to kill both actively multiplying and dormant bacteria, which typically takes several months even with multiple drugs. *To reduce bacterial load effectively* - Reducing bacterial load is certainly a goal of TB treatment, but the use of four drugs is specifically aimed at achieving this while simultaneously preventing **drug resistance**. - A single effective drug could reduce bacterial load, but it would quickly lead to the emergence of resistant bacteria, making the long-term goal of **cure** impossible. *None of the options* - This option is incorrect because the primary reason for a **four-drug regimen** in TB treatment is indeed to prevent the emergence of **drug-resistant strains**.

Question 1573: Which of the following is the treatment of choice for cryptococcal meningitis?

A. Fluconazole
B. Itraconazole
C. Flucytosine
D. Amphotericin B (Correct Answer)

Explanation: ***Amphotericin B*** - **Amphotericin B** is the **primary first-line antifungal agent** for severe fungal infections, including **cryptococcal meningitis**. - Current guidelines recommend **combination therapy with Amphotericin B plus Flucytosine** for induction therapy, with Amphotericin B being the **most critical component**. - Its broad spectrum of activity and ability to penetrate the **blood-brain barrier** make it highly effective against *Cryptococcus neoformans*. - **Liposomal Amphotericin B** is preferred due to reduced nephrotoxicity. *Fluconazole* - **Fluconazole** is an antifungal used for the **consolidation and maintenance phases** of cryptococcal meningitis treatment after initial induction therapy with Amphotericin B. - It is **not adequate as monotherapy** for the initial, acute management of severe cryptococcal meningitis due to slower fungicidal activity compared to Amphotericin B. *Itraconazole* - **Itraconazole** has **poor CNS penetration** and is generally **not recommended** for cryptococcal meningitis. - It is used for other fungal infections but is not part of standard treatment protocols for cryptococcal meningitis. *Flucytosine* - **Flucytosine** is an antifungal that is **always used in combination with Amphotericin B** (never alone) for cryptococcal meningitis to achieve a **synergistic effect** and improve outcomes. - It is **not used as monotherapy** because of rapid development of resistance when used alone. - While combination therapy is the gold standard, **Amphotericin B remains the primary agent**, making it the treatment of choice.

Question 1574: The following are live attenuated vaccines, except:

A. BCG
B. Oral typhoid
C. Measles
D. Pertussis (Correct Answer)

Explanation: ***Pertussis*** - The **pertussis vaccine** is an **inactivated (subunit) vaccine**, not a live attenuated vaccine. It contains purified components of the *Bordetella pertussis* bacteria. - Due to the high risk of severe complications, especially in infants, an inactivated vaccine is preferred to avoid any risk of active infection from a live vaccine. *BCG* - The **BCG (Bacille Calmette-Guérin) vaccine** is a **live attenuated vaccine** used to prevent tuberculosis. - It contains a live, weakened strain of *Mycobacterium bovis*. *Oral typhoid* - The **oral typhoid vaccine (Ty21a)** is a **live attenuated vaccine** designed to protect against *Salmonella Typhi*. - It consists of a live, weakened strain of the typhoid bacterium, taken orally. *Measles* - The **measles vaccine** (often given as part of the MMR vaccine) is a **live attenuated vaccine**. - It contains a weakened form of the measles virus, eliciting a strong immune response.

Question 1575: Which of the following aminoglycoside antibiotics has the highest risk of causing ototoxicity?

A. Amikacin
B. Kanamycin
C. Neomycin (Correct Answer)
D. Gentamicin

Explanation: ***Neomycin*** - **Neomycin** has the highest risk of **ototoxicity** among the aminoglycosides due to its significant accumulation in inner ear fluid. - It is typically reserved for **topical** or **oral administration** for local effects (e.g., bowel decontamination) to minimize systemic absorption and ototoxic risk [2]. *Kanamycin* - **Kanamycin** is an aminoglycoside with significant ototoxic potential, especially with prolonged use or high doses [1]. - While ototoxic, its risk is generally considered to be lower than Neomycin, which is rarely used systemically due to toxicity [1]. *Amikacin* - **Amikacin** is an aminoglycoside known for its broad spectrum of activity against resistant gram-negative bacteria, and it also carries a risk of ototoxicity [4]. - It is often used in severe infections, and its risk of ototoxicity is monitored, but it's not as high as neomycin [4]. *Gentamicin* - **Gentamicin** is a commonly used aminoglycoside for treating serious bacterial infections, and ototoxicity is a known adverse effect [3]. - While ototoxic, its relative risk is considered lower than neomycin and comparable to other commonly used aminoglycosides when therapeutic drug monitoring is employed [3].

Question 1576: What are the types of HPV vaccines that have been licensed and are available?

A. Monovalent
B. Trivalent
C. Only Quadrivalent
D. Bivalent, Quadrivalent, and Nonavalent (Correct Answer)

Explanation: ***Bivalent, Quadrivalent, and Nonavalent*** - Three types of HPV vaccines have been licensed: **bivalent** (2vHPV, Cervarix), **quadrivalent** (4vHPV, Gardasil), and **nonavalent** (9vHPV, Gardasil 9). - The **bivalent vaccine** protects against HPV types 16 and 18 (responsible for ~70% of cervical cancers). - The **quadrivalent vaccine** protects against HPV types 6, 11, 16, and 18 (also covers genital warts). - The **nonavalent vaccine** protects against nine HPV types (6, 11, 16, 18, 31, 33, 45, 52, 58) and is currently the most widely used, offering the broadest protection. *Monovalent* - This term refers to a vaccine targeting only **one specific strain** of a pathogen. - No HPV vaccine has ever been licensed as monovalent, as even the earliest vaccines covered multiple high-risk types. *Trivalent* - This describes a vaccine protecting against **three different strains** of a pathogen. - No **trivalent HPV vaccine** has ever been developed or licensed. *Only Quadrivalent* - While the **quadrivalent vaccine (Gardasil)** was an important advancement, it is not the only type available. - Both **bivalent** and **nonavalent** vaccines are also licensed and available globally.

Question 1577: All of the following beta-lactam antibiotics possess antipseudomonal action, except:

A. Ceftazidime
B. Cefoperazone
C. Piperacillin
D. Ceftriaxone (Correct Answer)

Explanation: ***Ceftriaxone*** - **Ceftriaxone** is a third-generation cephalosporin that has broad-spectrum activity but **lacks reliable antipseudomonal activity**. - While effective against many **Gram-positive** and **Gram-negative bacteria**, it is not a recommended choice for treating **Pseudomonas aeruginosa infections**. *Piperacillin* - **Piperacillin** is an extended-spectrum penicillin (often combined with **tazobactam**) known for its potent activity against **Pseudomonas aeruginosa**. - It is frequently used in empirical treatment of severe infections where **pseudomonal coverage** is critical. *Ceftazidime* - **Ceftazidime** is a third-generation cephalosporin specifically developed to have strong activity against **Pseudomonas aeruginosa**. - It is a key antibiotic in the treatment of **pseudomonal infections**, particularly those affecting the **lungs** or **urinary tract**. *Cefoperazone* - **Cefoperazone** is a third-generation cephalosporin that demonstrates good antipseudomonal activity, especially when combined with a **beta-lactamase inhibitor** like **sulbactam**. - It is used in the treatment of various infections caused by **P. aeruginosa** and other **Gram-negative bacteria**.

Question 1578: Rifampicin acts by inhibiting which of the following?

A. DNA Dependent RNA polymerase (Correct Answer)
B. RNA dependent DNA polymerase
C. Mycolic acid inhibition
D. Mycolic acid incorporation defects

Explanation: ***DNA Dependent RNA polymerase*** - **Rifampicin** works by binding to the **beta-subunit** of bacterial **DNA-dependent RNA polymerase**, preventing the initiation of RNA synthesis [2]. - This action is **bactericidal** and is crucial for its effectiveness against **Mycobacterium tuberculosis** and other bacteria [2]. *RNA dependent DNA polymerase* - This enzyme is also known as **reverse transcriptase** and is found in **retroviruses**, not bacteria [1]. - While it is a target for antiretroviral drugs, it is **not the target of rifampicin** [1]. *Mycolic acid inhibition* - **Mycolic acid** synthesis is a target for antitubercular drugs like **isoniazid**, which inhibits **mycolic acid production**. - Rifampicin does **not directly inhibit mycolic acid synthesis** but rather interferes with RNA transcription. *Mycolic acid incorporation defects* - This mechanism is characteristic of drugs like **ethambutol**, which interferes with the **polymerization of arabinogalactan**, thus hindering the proper incorporation of mycolic acid into the cell wall. - Rifampicin's mechanism of action is **distinct** from interfering with mycolic acid incorporation.

Question 1579: A patient diagnosed as having ventilator-associated pneumonia is on treatment with ceftriaxone and amikacin. Culture and sensitivity turned out to be positive for ESBL-producing Klebsiella infection. The most appropriate next action should be:

A. Continue same antibiotic but at higher dose
B. Change over to imipenem (Correct Answer)
C. Remove amikacin and add quinolone
D. Replace ceftriaxone with ceftazidime

Explanation: ***Change over to imipenem*** - **ESBL-producing bacteria** are resistant to most beta-lactam antibiotics, including ceftriaxone. **Carbapenems** like imipenem are the drugs of choice for severe infections caused by ESBL producers. - Switching to imipenem provides **effective empirical coverage** given the updated culture and sensitivity results, ensuring appropriate treatment for the multidrug-resistant organism. *Continue same antibiotic but at higher dose* - ESBL-producing bacteria are **resistant to ceftriaxone**, making it ineffective even at higher doses. - Increasing the dose of an ineffective antibiotic delays appropriate treatment and contributes to **antibiotic resistance**. *Replace ceftriaxone with ceftazidime* - Ceftazidime is also a **third-generation cephalosporin** and is generally ineffective against ESBL-producing organisms. - Switching to another cephalosporin would represent a continuation of **inappropriate antibiotic therapy**. *Remove amikacin and add quinolone* - While quinolones may have activity against some Gram-negative bacteria, their effectiveness against **ESBL-producing Klebsiella** is variable and often compromised by resistance. - **Amikacin** (an aminoglycoside) is a broad-spectrum antibiotic often used in combination for severe infections, and its removal without clear resistance or adverse effects may reduce coverage, especially for synergistic effects against multidrug-resistant organisms.

Question 1580: Which of the following is least appropriate for the treatment of tetanus?

A. Clindamycin
B. Penicillin
C. Doxycycline (Correct Answer)
D. Metronidazole

Explanation: ***Doxycycline*** - While doxycycline is an antibiotic, it is **not considered a primary agent** for treating tetanus due to its generally inferior efficacy against *Clostridium tetani* compared to other options. - The main goal of antibiotic therapy in tetanus is to **eradicate vegetative forms of C. tetani** at the wound site, to stop further toxin production, which doxycycline is not optimally suited for. *Clindamycin* - **Clindamycin** is an effective antibiotic against *Clostridium tetani* and is often used in combination with metronidazole. - Its mechanism of action involves **inhibiting bacterial protein synthesis**, thereby preventing bacterial growth and toxin production. *Penicillin* - **Penicillin** was historically a first-line antibiotic for tetanus due to its bactericidal activity against *C. tetani*. - However, some concerns exist about its potential to **exacerbate seizures** due to its GABA antagonism, leading to a preference for metronidazole. *Metronidazole* - **Metronidazole** is the antibiotic of choice for tetanus as it is highly effective against anaerobic bacteria like *C. tetani*. - It is preferred over penicillin due to its similar efficacy and **lack of CNS excitability effects**.

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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