Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1401: Treatment for filariasis is

A. Chloroquine
B. Praziquantel
C. Tetracycline
D. Diethyl Carbamazine (Correct Answer)

Explanation: ***Diethyl Carbamazine*** - **Diethyl Carbamazine (DEC)** is the drug of choice for treating lymphatic filariasis, acting against both microfilariae and adult worms. - It works by paralyzing the microfilariae and making them more susceptible to destruction by the host's immune system. *Chloroquin* - **Chloroquine** is an antimalarial drug used to treat malaria, a protozoal infection transmitted by mosquitoes, not filariasis. - Its primary mechanism involves interfering with the parasite's ability to detoxify heme. *Praziquantel* - **Praziquantel** is an anthelmintic agent primarily used to treat infections caused by **schistosomes** and **other flukes** and **tapeworms**. - It works by increasing the permeability of the worm's cell membranes to calcium, leading to paralysis and expulsion. *Tetracycline* - **Tetracycline** is a broad-spectrum antibiotic used to treat bacterial infections; it is not effective against **parasitic worms** like filaria. - It inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit.

Question 1402: Which of the following vaccines is currently used as a live attenuated vaccine in routine immunization programs?

A. Measles (Correct Answer)
B. Inactivated Polio Vaccine (IPV)
C. Smallpox
D. Cholera

Explanation: ***Measles***- The **measles vaccine** is a **live attenuated vaccine** that induces a strong and long-lasting immune response against the measles virus.- It is a core component of routine childhood immunization programs globally, often given as part of the **MMR (Measles, Mumps, Rubella)** vaccine.*Inactivated Polio Vaccine (IPV)*- **IPV** is an **inactivated (killed) vaccine** that contains polioviruses grown in culture and then chemically inactivated. [1]- It is administered via injection and produces systemic immunity without the risk of vaccine-associated paralytic poliomyelitis (VAPP).*Smallpox*- The **smallpox vaccine** contained a **live vaccinia virus**, which is related to smallpox but much safer.- While it was a live vaccine, smallpox has been eradicated, and routine vaccination is no longer practiced except for specific laboratory personnel.*Cholera*- Most commonly used cholera vaccines are either **inactivated (killed whole-cell)** vaccines or **live attenuated oral vaccines**.- While a live attenuated oral cholera vaccine exists, it is not part of routine childhood immunization programs in most countries, but rather used in specific outbreak settings or for travelers.

Question 1403: Which of the following is the preferred drug for prophylactic treatment of rheumatic heart disease?

A. Benzathine penicillin (Correct Answer)
B. Phenoxymethylpenicillin
C. Ampicillin
D. Penicillin G

Explanation: ***Benzathine penicillin*** - **Benzathine penicillin** is the **drug of choice** for the **prophylactic treatment of rheumatic heart disease** due to its prolonged action and superior compliance. - A single intramuscular injection provides therapeutic drug levels for **3-4 weeks**, making it ideal for **secondary prophylaxis** against recurrent Group A streptococcal infections. - **Superior adherence** compared to daily oral regimens, which is crucial for preventing rheumatic fever recurrence. *Phenoxymethylpenicillin* - **Phenoxymethylpenicillin** (Penicillin V) can be used as an **alternative** for RHD prophylaxis when IM injections are refused or impractical, requiring **daily oral dosing** (250 mg twice daily). - However, it is **less preferred** than benzathine penicillin due to **compliance issues** with daily dosing and the risk of missed doses compromising prophylaxis effectiveness. - The need for sustained, consistent blood levels makes the long-acting IM formulation significantly more reliable. *Ampicillin* - **Ampicillin** is a broader-spectrum penicillin used for treating various bacterial infections, but it is **not routinely used** for the prophylaxis of rheumatic heart disease. - Its shorter half-life and lack of long-acting formulations make it unsuitable for the sustained blood levels required for effective secondary prophylaxis against Group A Streptococcus. *Penicillin G* - **Penicillin G** (benzylpenicillin) is an injectable penicillin, but its half-life is **much shorter** than benzathine penicillin, requiring **frequent** intravenous or intramuscular administration (every 6-12 hours). - While effective for treating acute streptococcal infections, its short duration of action makes it **impractical** for the long-term, sustained prophylactic regimen needed to prevent recurrent rheumatic fever.

Question 1404: The standard regimen for satisfactory treatment of paucibacillary leprosy consists of

A. Dapsone and rifampicin for 6 months (Correct Answer)
B. Dapsone alone for 12 months
C. Dapsone and ethionamide for 12 months
D. Dapsone and clofazimine for 6 months

Explanation: ***Dapsone and rifampicin for 6 months*** - The standard **multidrug therapy (MDT)** for **paucibacillary (PB) leprosy** involves a combination of **Dapsone** and **Rifampicin**. - This regimen is administered for a duration of **6 months** to achieve satisfactory treatment and prevent resistance. *Dapsone alone for 12 months* - **Monotherapy** with Dapsone is **not recommended** for leprosy due to the high risk of developing **drug resistance**. - While Dapsone is a component, it must be combined with other drugs. *Dapsone and ethionamide for 12 months* - **Ethionamide** is typically used as a second-line drug, primarily in cases of **multidrug-resistant leprosy** or specific treatment failures. - It is not part of the standard initial regimen for paucibacillary leprosy. *Dapsone and clofazimine for 6 months* - The combination of **Dapsone and Clofazimine** is part of the standard regimen for **multibacillary (MB) leprosy**, not paucibacillary. - While Clofazimine is effective, it is withheld for PB leprosy to minimize drug burden and side effects, as these patients have a lower bacterial load.

Question 1405: Thalidomide is drug of choice for -

A. Nerve abscess
B. Lepra I reaction
C. Lepra II reaction (Correct Answer)
D. Both

Explanation: ***Lepra II reaction*** - **Thalidomide** is highly effective in treating **erythema nodosum leprosum (ENL)**, also known as Lepra II reaction. - It works by modulating the immune response, reducing the severe inflammatory symptoms. *Nerve abscess* - **Nerve abscesses** in leprosy usually require surgical drainage and appropriate antibiotic treatment, not thalidomide. - They represent a localized collection of pus within a nerve, often associated with a **Type I reaction**. *Lepra I reaction* - **Type I reactions** (reversal reactions) are typically managed with corticosteroids to reduce inflammation and prevent nerve damage. - Thalidomide is not the primary treatment for these reactions, as their underlying immunological mechanism differs from Type II reactions. *Both* - Thalidomide is specific to **Lepra II reactions (ENL)** and is not the drug of choice for nerve abscesses or Lepra I reactions. - Treating both conditions with thalidomide would be inappropriate given their distinct pathologies and treatment protocols.

Question 1406: Neurological complications following rabies vaccine are common with

A. HDCS Vaccine
B. Chick embryo Vaccine
C. Semple Vaccine (Correct Answer)
D. Duck Egg Vaccine

Explanation: ***Semple Vaccine*** - The **Semple vaccine (nerve tissue vaccine)** is associated with a higher incidence of **neurological complications** due to sensitisation to neural tissue components. - These complications can include **demyelinating encephalomyelitis** and paralysis, making it a less safe option compared to modern vaccines. *HDCS Vaccine* - The **Human Diploid Cell Vaccine (HDCV)** is a modern, highly purified rabies vaccine with a significantly **lower risk of neurological complications**. - It is considered one of the **safest and most effective** rabies vaccines available, rarely causing severe adverse events. *Chick embryo Vaccine* - **Chick embryo vaccines (CEV)** are produced in avian embryos and generally have a **low incidence of neurological complications** compared to nerve tissue vaccines. - While safer than older formulations, they are typically less used now than cell culture vaccines. *Duck Egg Vaccine* - **Duck embryo vaccines (DEV)** were an improvement over nerve tissue vaccines, offering a **reduced risk of neurological side effects**. - However, they still carried a slightly higher risk of adverse reactions compared to modern cell culture-derived vaccines.

Question 1407: Drug of choice for chemoprophylaxis in meningococcal meningitis is -

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

Explanation: ***Rifampicin*** - **Rifampicin** is a primary agent for **chemoprophylaxis** against **meningococcal meningitis** due to its effective penetration into the cerebrospinal fluid and elimination of nasopharyngeal carriage of *Neisseria meningitidis*. - It is often favored for its **convenient oral administration** and short treatment course, making it suitable for close contacts of patients. *Tetracycline* - **Tetracycline** is not the **drug of choice** for **meningococcal prophylaxis** because of potential resistance patterns and side effects, especially in children and pregnant women. - While broad-spectrum, its efficacy against *Neisseria meningitidis* carriage is generally less reliable than recommended agents. *Erythromycin* - **Erythromycin** is not the preferred antibiotic for **meningococcal chemoprophylaxis** due to its variable efficacy in eradicating the nasopharyngeal carriage of *Neisseria meningitidis*. - Other agents like rifampicin or ceftriaxone are more consistently effective. *Streptomycin* - **Streptomycin** is an **aminoglycoside antibiotic** primarily used for **tuberculosis** and severe bacterial infections, but it is not effective for **meningococcal prophylaxis**. - It has a narrow spectrum against *Neisseria meningitidis* and does not achieve adequate concentrations in the nasopharynx to prevent carriage.

Question 1408: A 25 year old female, presents to the clinic with dysuria, urinary frequency and urgency. After a laboratory workup a diagnosis of cystitis is made. Which is the first line drug for the treatment for this patient?

A. Cephalexin
B. Norfloxacin
C. Amoxicillin
D. Nitrofurantoin (Correct Answer)

Explanation: ***Nitrofurantoin*** - **Nitrofurantoin** is the most widely recommended first-line antibiotic for uncomplicated **cystitis** due to its excellent efficacy against common urinary pathogens, especially **E. coli**. - It achieves high concentrations in the urine and has a low rate of resistance, making it an excellent choice for this condition. - It is preferred over other antibiotics due to antimicrobial stewardship principles and minimal impact on gut flora. *Cephalexin* - While generally effective against some urinary pathogens, **cephalexin** is typically reserved as a second-line agent for uncomplicated cystitis, particularly if there are contraindications to or resistance to first-line agents. - Its broad-spectrum activity may contribute to increased resistance development if used routinely as first-line. *Norfloxacin* - **Norfloxacin** is a **fluoroquinolone** that, while effective for UTIs and sometimes used in regional practice, is generally not recommended as the preferred first-line for uncomplicated cystitis due to concerns about increasing antibiotic resistance and potential for serious side effects (e.g., tendinitis, QT prolongation, CNS effects). - Current antimicrobial stewardship guidelines recommend reserving fluoroquinolones for more complicated urinary tract infections or when other first-line options are not suitable. *Amoxicillin* - **Amoxicillin** is generally not recommended as a first-line agent for cystitis due to high rates of **bacterial resistance**, particularly among **E. coli** strains, which are the most common cause of UTIs. - Its efficacy against common urinary pathogens is often lower compared to other first-line options.

Question 1409: Most common drug used in Leprosy is :

A. Ethionamide
B. Dapsone (Correct Answer)
C. Ofloxacin
D. Clofazimine

Explanation: ***Correct Answer: Dapsone*** - **Dapsone** is the most commonly used and foundational drug in **multidrug therapy (MDT)** for leprosy [1] - It is included in **all WHO-recommended MDT regimens** for both paucibacillary and multibacillary leprosy [1] - Acts as a **bacteriostatic agent** against **Mycobacterium leprae** by interfering with **folate synthesis** [3] - Well-tolerated with a favorable safety profile for long-term use [2] - Has been the backbone of leprosy treatment for decades [1] *Incorrect: Ethionamide* - **Ethionamide** is primarily a **second-line agent for tuberculosis**, especially in multidrug-resistant TB (MDR-TB) - Not a standard drug for leprosy due to higher toxicity and availability of more effective options - Has no role in routine leprosy treatment regimens *Incorrect: Ofloxacin* - **Ofloxacin** is a **fluoroquinolone antibiotic** with some activity against **Mycobacterium leprae** - Used only as an **alternative agent** in special circumstances (e.g., drug resistance or intolerance) - Not part of standard first-line MDT regimens for leprosy *Incorrect: Clofazimine* - **Clofazimine** is an important component of **multibacillary (MB) leprosy treatment** in WHO MDT regimens [2] - While essential for MB leprosy, it is **not used in paucibacillary (PB) leprosy** regimens [1] - **Dapsone** is more commonly used overall as it appears in **all MDT regimens** (both PB and MB), making it the most common drug in leprosy treatment [1]

Question 1410: A person wants to visit a malaria endemic area of low level chloroquine resistant falciparum malaria. The best chemoprophylaxis is -

A. Sulfadoxine + Pyrimethamine
B. Mefloquine
C. Atovaquone + Proguanil (Correct Answer)
D. Chloroquine

Explanation: ***Atovaquone + Proguanil*** - **Atovaquone + Proguanil (Malarone)** is the **preferred first-line chemoprophylaxis** for areas with **chloroquine-resistant *P. falciparum***, including low-level resistance. - It has **excellent efficacy** against resistant strains with minimal documented resistance, and is **well-tolerated** with fewer side effects compared to mefloquine. - Approved by WHO and CDC as a **primary option** for travelers to chloroquine-resistant malaria areas. - The daily dosing regimen, while requiring more frequent administration, actually allows for a **shorter pre-travel start time** (1-2 days before vs. 1-2 weeks for mefloquine) and **shorter post-travel duration** (7 days vs. 4 weeks). *Mefloquine* - While **effective against chloroquine-resistant *P. falciparum***, mefloquine is increasingly used as a **second-line option** due to significant **neuropsychiatric side effects** (anxiety, depression, vivid dreams, rarely psychosis). - It requires weekly dosing starting 2 weeks before travel and continuing 4 weeks after, making the total prophylaxis period longer. - **Contraindicated** in individuals with psychiatric disorders, seizure disorders, or cardiac conduction abnormalities. *Sulfadoxine + Pyrimethamine* - This combination is primarily used for **intermittent preventive treatment (IPT)** in pregnant women and infants in endemic areas, **not for travel prophylaxis**. - Widespread **parasitic resistance** to both components has made it unreliable for chemoprophylaxis in most regions. - Not recommended by international guidelines for routine traveler prophylaxis. *Chloroquine* - **Completely ineffective** in areas with **chloroquine-resistant *P. falciparum*** as stated in the question. - Would provide **no protection** and lead to treatment failure if infection occurs.

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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