Antimicrobial Agents Practice Questions

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

B.C.G.. ***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.

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

Piperazine. ***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.

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

Oseltamivir. ***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].

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

Benzathine Benzyl Penicillin. ***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.

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

It is a bacteriostatic drug. ***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.

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

Lower resistance rates. ***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

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

Gardasil. ***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).

Q: 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?

Acyclovir-resistant HSV strain. **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.

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

Doxycycline. ***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.

Question 1

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

Accepted Answer

B.C.G.

Answer

D.P.T.

Answer

Hepatitis ‘B’

Answer

Typhoid (TAB)

Question 2

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

Accepted Answer

Piperazine

Answer

Albendazole

Answer

Levamisole

Answer

Pyrantel

Question 3

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

Accepted Answer

Oseltamivir

Answer

Ribavirin

Answer

Amantadine

Answer

Zanamivir

Question 4

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

Accepted Answer

Benzathine Benzyl Penicillin

Answer

Doxycycline

Answer

Procaine Penicillin

Answer

Ciprofloxacin

Question 5

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

Accepted Answer

It is a bacteriostatic drug

Answer

It has extended half life

Answer

It specifically targets mycobacterial ATP synthase

Answer

It has high volume of tissue distribution

Question 6

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

Accepted Answer

It can be administered till 15 days after the first dose of anti-rabies vaccine

Answer

It should be administered primarily into or around the wound sites

Answer

There is no scientific ground for performing a skin test prior to administering equine immunoglobulin

Answer

It should be administered only once as soon as possible after the initiation of post exposure prophylaxis

Question 7

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

Accepted Answer

Lower resistance rates

Answer

Single-dose convenience

Answer

Better tissue penetration

Answer

Lower risk of allergic reactions

Question 8

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

Accepted Answer

Gardasil

Answer

Shingrix

Answer

Gardasil 9

Answer

Cervarix

Question 9

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?

Accepted Answer

Acyclovir-resistant HSV strain

Answer

Immunologic factors reducing drug efficacy

Answer

Incorrect diagnosis of herpes

Answer

Superinfection with a different HSV type

Question 10

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

Accepted Answer

Doxycycline

Answer

Azithromycin

Answer

Amoxicillin

Answer

Erythromycin

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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