Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1311: Which of the following is an example of ‘live attenuated vaccine’?

A. D.P.T.
B. Hepatitis ‘B’
C. Typhoid (TAB)
D. B.C.G. (Correct Answer)

Explanation: ***B.C.G.*** - The **Bacillus Calmette-Guérin (BCG)** vaccine is a **live attenuated vaccine** used worldwide for **tuberculosis prevention**. - It contains a live, but weakened, strain of *Mycobacterium bovis*, which stimulates a strong cellular immune response. *D.P.T.* - The **DPT vaccine** is a **combination vaccine** for diphtheria, pertussis (whooping cough), and tetanus. - It is currently available as an **inactivated vaccine**, specifically a **toxoid for diphtheria and tetanus** and either a whole-cell or acellular component for pertussis. *Hepatitis ‘B’* - The **Hepatitis B vaccine** is a **recombinant vaccine**, meaning it is produced using genetic engineering techniques. - It contains only the **surface antigen protein** of the Hepatitis B virus, not the whole virus, making it a non-live vaccine. *Typhoid (TAB)* - The **Typhoid (TAB) vaccine** is an **inactivated (killed) whole-cell vaccine** against *Salmonella Typhi*. - Newer typhoid vaccines, such as the polysaccharide vaccine and conjugate vaccine, are also non-live vaccines.

Question 1312: All of the following drugs are effective for treatment of hookworm infection in single dose EXCEPT:

A. Albendazole
B. Levamisole
C. Pyrantel
D. Piperazine (Correct Answer)

Explanation: ***Piperazine*** - **Piperazine** is primarily effective against **Ascaris lumbricoides** and **Enterobius vermicularis**, acting as a depolarizing neuromuscular blocker. - It is **not effective** against hookworm infections and is therefore unsuitable for treating the human reservoir of hookworms. *Albendazole* - **Albendazole** is a broad-spectrum anthelminthic highly effective against hookworm infections, including **Necator americanus** and **Ancylostoma duodenale**. - A **single dose** is often sufficient due to its effectiveness in eliminating adult worms and reducing egg excretion. *Levamisole* - **Levamisole** is an anthelminthic that can be effective against hookworm species, working as a **ganglionic stimulant** causing paralysis of the worms. - A **single dose** regimen is typically adequate for hookworm treatment. *Pyrantel* - **Pyrantel pamoate** is effective against hookworms by causing **neuromuscular blockade**, leading to expulsion of the worms. - It is often given as a **single dose** for effective treatment of hookworm infections.

Question 1313: The drug of choice for chemoprophylaxis to health care personnel and close contacts of suspected or confirmed case of pandemic influenza A (H1N1) is:

A. Ribavirin
B. Oseltamivir (Correct Answer)
C. Amantadine
D. Zanamivir

Explanation: ***Oseltamivir*** - **Oseltamivir** is the recommended drug for chemoprophylaxis against pandemic influenza A (H1N1) for healthcare personnel and close contacts [1, 2]. - This recommendation is based on its effectiveness against the **neuraminidase** of the H1N1 virus, preventing viral release and spread. *Ribavirin* - **Ribavirin** is an antiviral agent used for conditions like chronic hepatitis C and RSV, but it is not recommended for influenza chemoprophylaxis. - Its mechanism of action and efficacy profile do not make it a primary choice for preventing H1N1 infection. *Amantadine* - **Amantadine** targets the M2 ion channel of influenza A viruses, but many H1N1 strains, including the pandemic strain, developed **resistance** to this drug [1]. - Due to widespread resistance, **amantadine** and rimantadine are no longer recommended for routine influenza treatment or prophylaxis [1]. *Zanamivir* - **Zanamivir** is another **neuraminidase inhibitor** effective against influenza A and B, but it is administered via inhalation. - While effective, **oseltamivir** is generally preferred for chemoprophylaxis due to its oral administration, making it more convenient for widespread use [2].

Question 1314: Which one of the following is the antibiotic of choice for the prevention of Rheumatic Heart Disease?

A. Benzathine Benzyl Penicillin (Correct Answer)
B. Doxycycline
C. Procaine Penicillin
D. Ciprofloxacin

Explanation: ***Benzathine Benzyl Penicillin*** - It is the antibiotic of choice for the **prevention of Rheumatic Heart Disease (RHD)** due to its **long-acting nature** and effectiveness against **Group A Streptococcus (GAS)**. - A single intramuscular injection provides **sustained therapeutic levels** for several weeks, crucial for preventing recurrent GAS infections that lead to RHD. *Doxycycline* - Not effective for **primary prevention of Rheumatic Fever** or RHD as it is not a first-line agent against **Group A Streptococcus**. - Mainly used for **atypical bacteria** and certain parasitic infections. *Procaine Penicillin* - It has a shorter duration of action compared to **benzathine penicillin**. - Requires more frequent injections, making it less suitable for **long-term prophylaxis** in RHD prevention. *Ciprofloxacin* - This is a **fluoroquinolone antibiotic** and is not the antibiotic of choice for **Group A Streptococcus infections**. - Its use in this context could contribute to **antibiotic resistance** without providing effective prophylaxis for RHD.

Question 1315: All of the following are true about Bedaquiline (BDQ) EXCEPT:

A. It has extended half life
B. It is a bacteriostatic drug (Correct Answer)
C. It specifically targets mycobacterial ATP synthase
D. It has high volume of tissue distribution

Explanation: ***It is a bacteriostatic drug*** - **Bedaquiline (BDQ)** is a novel anti-tuberculosis drug that is **bactericidal** against *Mycobacterium tuberculosis*, meaning it kills the bacteria rather than just inhibiting their growth. - Its bactericidal action is crucial for treating multi-drug resistant (MDR) and extensively drug-resistant (XDR) tuberculosis. *It has extended half-life* - **Bedaquiline** has a very **long terminal elimination half-life**, which can extend up to several months. - This extended half-life allows for less frequent dosing schedules (e.g., once daily or thrice weekly after an initial loading phase). *It specifically targets mycobacterial ATP synthase* - **Bedaquiline** specifically inhibits **mycobacterial ATP synthase**, an enzyme essential for energy production in *Mycobacterium tuberculosis* [1]. - This unique mechanism of action contributes to its effectiveness against traditional drug-resistant strains [1]. *It has high volume of tissue distribution* - **Bedaquiline** is highly lipophilic and extensively distributed into tissues, resulting in a **large volume of distribution**. - This extensive tissue distribution contributes to its long half-life and allows it to reach therapeutic concentrations within the infection sites.

Question 1316: Which one of the following statements regarding Rabies Immunoglobulin is NOT true?

A. It should be administered primarily into or around the wound sites
B. There is no scientific ground for performing a skin test prior to administering equine immunoglobulin
C. It can be administered till 15 days after the first dose of anti-rabies vaccine (Correct Answer)
D. It should be administered only once as soon as possible after the initiation of post exposure prophylaxis

Explanation: ***It can be administered till 15 days after the first dose of anti-rabies vaccine*** - This statement is **incorrect** because Rabies Immunoglobulin (RIG) provides passive immunity and should be given as soon as possible after exposure, ideally within **7 days** of the first vaccine dose. Beyond this period, the vaccine itself is expected to have stimulated active immunity. - Delaying RIG administration significantly reduces its effectiveness, as the goal is to neutralize the virus before the body mounts its own immune response, which typically begins to be robust around day 7-10 after vaccination. *It should be administered primarily into or around the wound sites* - This statement is **true**. The primary goal of RIG is to provide immediate, localized immunity by neutralizing the rabies virus at the site of entry. - Infiltrating as much of the dose as anatomically feasible directly into and around the wound ensures effective local virus neutralization. *There is no scientific ground for performing a skin test prior to administering equine immunoglobulin* - This statement is **true** according to current WHO guidelines. With modern, highly purified RIG products, the risk of severe systemic allergic reactions is low. - Skin testing can be unreliable, lead to unnecessary delays in critical post-exposure prophylaxis, and may not accurately predict a severe allergic reaction. *It should be administered only once as soon as possible after the initiation of post exposure prophylaxis* - This statement is **true**. RIG is a single-dose treatment given at the beginning of post-exposure prophylaxis (PEP) to provide immediate antibodies. - Multiple doses are not recommended as they could interfere with the development of the body's active immune response stimulated by the rabies vaccine.

Question 1317: Why is ceftriaxone preferred over penicillin for gonorrhea treatment despite both being effective in vitro?

A. Single-dose convenience
B. Better tissue penetration
C. Lower resistance rates (Correct Answer)
D. Lower risk of allergic reactions

Explanation: ***Lower resistance rates*** - The **primary reason** ceftriaxone is preferred over penicillin for gonorrhea is the **widespread emergence of penicillinase-producing *Neisseria gonorrhoeae* (PPNG)** strains and chromosomally-mediated resistance - Penicillin resistance in *N. gonorrhoeae* now exceeds **50-90%** in many regions globally, making penicillin ineffective for empirical treatment - **Ceftriaxone** and other third-generation cephalosporins maintain **high efficacy** against most gonorrhea strains, though emerging cephalosporin resistance is a growing concern - Current **CDC and WHO guidelines** recommend ceftriaxone as first-line therapy specifically because of superior antimicrobial activity against resistant strains *Single-dose convenience* - While ceftriaxone's **single intramuscular dose** regimen does improve patient adherence and treatment completion, this is a **secondary advantage** - Convenience is clinically irrelevant if the drug is ineffective due to resistance - The single-dose feature enhances the utility of ceftriaxone but is not the fundamental reason for its preference over penicillin *Lower risk of allergic reactions* - Ceftriaxone does not have a significantly lower risk of allergic reactions compared to penicillin - Both penicillins and cephalosporins share a **beta-lactam structure**, leading to potential **cross-reactivity** (5-10% in penicillin-allergic patients) - Allergy considerations are important for individual patient selection but do not explain the population-level preference for ceftriaxone *Better tissue penetration* - Both **ceftriaxone** and penicillin achieve adequate tissue penetration at sites of gonorrheal infection (urethra, cervix, rectum, pharynx) - Ceftriaxone does have excellent CNS penetration and longer half-life, but tissue penetration differences are **not the primary factor** in choosing it over penicillin for uncomplicated gonorrhea

Question 1318: Which quadivalent HPV vaccine protects against both cervical cancer and genital warts?

A. Shingrix
B. Gardasil 9
C. Cervarix
D. Gardasil (Correct Answer)

Explanation: ***Gardasil***- This **quadrivalent** vaccine protects against **HPV types 6, 11, 16, and 18**. [1]- **HPV 16 and 18** are responsible for most cases of **cervical cancer**, while **HPV 6 and 11** cause approximately 90% of **genital warts**. [1]- Gardasil was the first quadrivalent HPV vaccine approved and remains widely used globally.*Shingrix*- **Shingrix** is a recombinant zoster vaccine used to prevent **herpes zoster (shingles)** in adults.- It is **not an HPV vaccine** and does not provide protection against cervical cancer or genital warts.- It targets varicella-zoster virus, not human papillomavirus.*Gardasil 9*- **Gardasil 9** is a **nonavalent** vaccine, meaning it protects against nine HPV types (6, 11, 16, 18, 31, 33, 45, 52, and 58).- While it does cover the types responsible for cervical cancer and genital warts, it is **not a quadrivalent vaccine** as specified in the question.*Cervarix*- **Cervarix** is a **bivalent** HPV vaccine that protects against **HPV types 16 and 18** only. [1]- While it offers protection against the HPV types most commonly associated with **cervical cancer**, it does not protect against **genital warts** (caused by HPV 6 and 11).

Question 1319: A 30-year-old woman presents with breakthrough genital herpes outbreaks despite appropriate suppressive therapy. She is HIV-negative and reports adherence to medication. What is the most likely explanation?

A. Immunologic factors reducing drug efficacy
B. Incorrect diagnosis of herpes
C. Superinfection with a different HSV type
D. Acyclovir-resistant HSV strain (Correct Answer)

Explanation: **Acyclovir-resistant HSV strain** - Given recurrent outbreaks despite suppressive therapy and reported adherence, **drug resistance (e.g., acyclovir resistance)** is the most likely explanation for treatment failure [1]. - Acyclovir resistance typically occurs due to mutations in the **viral thymidine kinase gene**, preventing activation of the drug [1]. *Immunologic factors reducing drug efficacy* - While underlying immune status can affect herpes recurrence, the patient is **HIV-negative**, suggesting a relatively intact immune system. - Suppressive therapy is designed to overcome standard immune responses, so general immunologic factors alone are less likely to cause complete suppressive failure in an otherwise healthy individual [2]. *Incorrect diagnosis of herpes* - Recurrent genital lesions often lead to a high suspicion of herpes, and the initiation of suppressive therapy implies a **prior clinical diagnosis**. - While misdiagnosis is possible, given the history of recurrent outbreaks and *initiation of suppressive therapy*, an incorrect diagnosis is less probable than resistance when the treatment itself is failing. *Superinfection with a different HSV type* - While possible, superinfection with another HSV type (e.g., HSV-1 if initially HSV-2, or vice versa) would typically present with **new primary-like symptoms** or a renewed pattern of outbreaks, not necessarily a direct failure of *ongoing suppressive therapy* for the existing type. - Suppressive therapy against one HSV type usually offers *some cross-protection* or at least would not completely fail against the *original* type due to a new infection.

Question 1320: Which oral antibiotic is contraindicated in pregnant women with chlamydial infection?

A. Azithromycin
B. Amoxicillin
C. Erythromycin
D. Doxycycline (Correct Answer)

Explanation: ***Doxycycline*** - **Doxycycline** is contraindicated in pregnant women due to its potential to cause **permanent tooth discoloration** (yellow-brown staining) and **enamel hypoplasia** in the fetus. - It can also inhibit **bone growth** if used during pregnancy, making it an unsuitable choice for chlamydial infection in this population. *Azithromycin* - **Azithromycin** is generally considered safe and is a recommended treatment for **chlamydial infection in pregnant women**. - It is a **macrolide antibiotic** and does not have the teratogenic effects associated with tetracyclines like doxycycline. *Amoxicillin* - **Amoxicillin** is a **penicillin-class antibiotic** and is considered safe for use during pregnancy. - While it can be used for some infections in pregnancy, it is not the primary treatment for **chlamydial infections**, for which macrolides are preferred. *Erythromycin* - **Erythromycin** is another **macrolide antibiotic** that is considered safe for use in pregnant women. - It is an alternative treatment option for **chlamydial infection during pregnancy**, particularly if azithromycin is not tolerated.

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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