Antimicrobial Agents Practice Questions

Q: Drug of choice for Pneumocystis jirovecii in pregnancy?

Trimethoprim-sulfamethoxazole (SMZ/TMP). ***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.

Q: Which of the following is not used as treatment for lymphatic filariasis -

Praziquantel. ***Praziquantel*** - **Praziquantel** is primarily an **anthelmintic drug** effective against **schistosomiasis** and **tapeworm infections**. - It does not have a significant role in the treatment of **lymphatic filariasis**. *Ivermectin* - **Ivermectin** is one of the **mainstays** of treatment for **lymphatic filariasis**, particularly in combination therapies. - It works by paralyzing and killing **microfilariae**, reducing their numbers in the bloodstream. *DEC* - **Diethylcarbamazine (DEC)** is a **highly effective antifilarial drug** used to kill both **microfilariae** and **adult worms** in lymphatic filariasis. - It is often used in mass drug administration programs and for individual treatment. *Albendazole* - **Albendazole** is an **anthelmintic drug** often used in combination with **Ivermectin** or **DEC** for the treatment of **lymphatic filariasis**. - It helps to kill **microfilariae** and has some macrofilaricidal effects, reducing the viability of adult worms.

Q: What is the primary reason for using a combination of four drugs in Anti-Koch's Treatment (AKT) for tuberculosis?

To decrease the risk of resistance due to mutation.. ***To decrease the risk of resistance due to mutation*** - **Tuberculosis bacteria** can spontaneously develop resistance to a single drug through **random genetic mutations**. - Using multiple drugs simultaneously significantly reduces the probability that a bacterium will spontaneously develop resistance to **all drugs** in the regimen. - This is the **primary rationale** for multi-drug therapy in TB, as emphasized by WHO guidelines. *To decrease the risk of resistance due to conjugation* - **Conjugation** is a mechanism of horizontal gene transfer in bacteria, primarily involving the transfer of plasmids. - While important for antibiotic resistance in some bacteria, it is **not the primary mechanism** of resistance development in *Mycobacterium tuberculosis*. - TB resistance develops mainly through **chromosomal mutations**, not plasmid transfer. *To enhance overall treatment efficacy* - While multi-drug regimens do enhance treatment efficacy by targeting different bacterial populations (actively dividing, slow-growing, dormant), this is a **consequence** of the multi-drug approach. - The **primary reason** for using four drugs specifically is to prevent the emergence of **drug-resistant mutants**. - Enhanced efficacy is achieved *because* resistance is prevented, making this a secondary benefit. *To simplify treatment* - A four-drug regimen actually makes treatment more **complex** due to multiple pills, potential drug interactions, and increased side effects. - The complexity is a necessary trade-off for **resistance prevention** and treatment success.

Q: All are true about ciprofloxacin except?

More active at acidic pH. ***More active at acidic pH*** - Fluoroquinolones, including ciprofloxacin, exhibit **reduced antibacterial activity in acidic environments**. Their efficacy is generally better at **neutral or alkaline pH**. - This is clinically relevant as fluoroquinolones may have **reduced effectiveness in acidic sites** like the stomach or acidic urine. - The optimal antibacterial activity occurs at physiological or slightly alkaline pH. *DNA gyrase inhibition* - Ciprofloxacin, like other fluoroquinolones, exerts its antibacterial effect by inhibiting **bacterial DNA gyrase (topoisomerase II)** and **topoisomerase IV**. - This inhibition prevents DNA replication and repair, leading to bacterial cell death. *Contraindicated in pregnancy* - Ciprofloxacin is generally **contraindicated in pregnancy** due to concerns about potential harm to the developing fetus, particularly effects on **cartilage development**. - However, it may be used in specific, life-threatening situations if the benefit outweighs the potential risk. *Second generation fluoroquinolone* - Ciprofloxacin is classified as a **second-generation fluoroquinolone**. - This class includes agents with improved activity against Gram-negative bacteria and some atypical organisms.

Q: As per RNTCP guidelines, Multi drug resistance (MDR) TB is defined as resistance to:

Rifampicin and isoniazid. ***Rifampicin and isoniazid*** - According to **RNTCP guidelines** (now NTEP), **MDR-TB** is specifically defined as tuberculosis that is resistant to at least both **rifampicin** and **isoniazid**. - These two drugs are the **most potent first-line anti-TB medications**, and resistance to both significantly complicates treatment. *Rifampicin* - While resistance to **rifampicin alone** is a serious concern, it is classified as **rifampicin-resistant TB (RR-TB)**, not full **MDR-TB**. - **MDR-TB** requires resistance to at least two key first-line drugs. *Rifampicin, isoniazid and ethambutol* - Resistance to **rifampicin**, **isoniazid**, and **ethambutol** would be a form of **MDR-TB** (as it includes resistance to rifampicin and isoniazid), but it is a more extensive form of resistance. - The minimum definition of **MDR-TB** focuses on the two most crucial first-line drugs. *None of the above* - This option is incorrect because there is a specific definition for **MDR-TB** that aligns with one of the provided choices. - The guidelines clearly define **MDR-TB** based on resistance to specific drugs.

Q: Which sulphonamide has the longest acting duration?

Sulphadoxine. ***Sulphadoxine*** - **Sulphadoxine** is known for its **exceptionally long elimination half-life**, which is due to its high plasma protein binding and slow renal excretion. - This property allows for **once-weekly dosing**, making it one of the longest-acting sulfonamides, often used in combinations for malaria prophylaxis or treatment. *Sulfadiazine* - **Sulfadiazine** has an intermediate half-life, typically requiring **multiple daily doses**. - It is commonly used for infections like **toxoplasmosis** and **nocardiosis**. *Sulfamethoxazole* - **Sulfamethoxazole** has an intermediate half-life, usually requiring **twice-daily administration**. - It is most famously co-formulated with **trimethoprim** (as co-trimoxazole) for a broad range of bacterial infections. *Sulfamethiazole* - **Sulfamethiazole** is a **short-acting sulfanilamide derivative** with a rapid elimination, meaning it would require frequent dosing. - It is not commonly used systemically due to its short duration of action.

Q: Which antibiotic is Actinomycosis sensitive to?

Penicillin. ***Penicillin*** - **Penicillin** is the **antibiotic of choice** for treating Actinomycosis due to the organism's high sensitivity. - Treatment typically involves a **long course** of high-dose penicillin for several months. *Streptomycin* - **Streptomycin** is an **aminoglycoside antibiotic** primarily used for **tuberculosis** and some gram-negative bacterial infections. - It is **not effective** against Actinomyces species. *Nystatin* - **Nystatin** is an **antifungal medication** used to treat **yeast infections**, particularly Candida. - It has **no antibacterial activity** and thus no role in treating Actinomycosis. *Doxycycline* - While **doxycycline** can be used as an **alternative** in patients allergic to penicillin, it is **not the primary choice**. - Its effectiveness is generally less pronounced than penicillin, and it's reserved for second-line treatment.

Q: Which type of vaccine is used for chicken pox?

Live vaccine. ***Live vaccine*** - The chickenpox vaccine (Varicella vaccine) is a **live-attenuated vaccine**, meaning it contains a weakened form of the **Varicella-zoster virus** (Oka strain). - This weakened virus can still replicate in the body, stimulating a strong and long-lasting immune response similar to natural infection but without causing severe disease. *Killed vaccine* - **Killed (inactivated) vaccines** use viruses or bacteria that have been inactivated through heat or chemicals, making them unable to replicate. - While effective for some diseases (e.g., inactivated polio, influenza), they typically require **multiple doses** and might provide less durable immunity compared to live vaccines. *Conjugated vaccine* - **Conjugated vaccines** are designed to improve the immune response to polysaccharide antigens (e.g., bacterial capsules) by linking them to a carrier protein. - This technology is primarily used for **bacterial infections** like *Haemophilus influenzae* type b (Hib) or pneumococcal disease, not viral illnesses like chickenpox. *Toxoid vaccine* - **Toxoid vaccines** contain inactivated bacterial toxins (toxoids) rather than the whole organism. - Examples include **tetanus and diphtheria vaccines**, which protect against diseases caused by bacterial toxins, not viral infections like chickenpox.

Q: What is the mechanism of action of quinolones?

Inhibit DNA gyrase. ***Inhibit DNA gyrase*** - Quinolones, particularly **fluoroquinolones**, exert their bactericidal effect by targeting **bacterial DNA gyrase (topoisomerase II)** and **topoisomerase IV**. - This inhibition prevents the uncoiling and replication of bacterial DNA, leading to cell death. *Bind to 30S ribosomal subunit* - This mechanism is characteristic of **aminoglycosides** and **tetracyclines**, which disrupt bacterial protein synthesis. - Quinolones do not interfere with ribosomal function but rather with **DNA replication**. *Bind to bacterial cell membrane* - This is the mechanism of action for **polymyxins** and **daptomycin**, which disrupt the integrity of the bacterial cell membrane. - Quinolones specifically target **intracellular enzymes** involved in DNA handling. *Inhibit tetrahydrofolate reductase* - This enzyme name in the option is technically imprecise; **trimethoprim** actually inhibits **dihydrofolate reductase**, which is part of the **sulfonamide-trimethoprim (Bactrim)** combination. - This pathway is involved in **folic acid synthesis**, crucial for bacterial DNA and RNA production, a mechanism distinct from quinolones.

Question 1

Drug of choice for Pneumocystis jirovecii in pregnancy?

Accepted Answer

Trimethoprim-sulfamethoxazole (SMZ/TMP)

Answer

Primaquine

Answer

Dapsone

Answer

Pentamidine

Question 2

What is the best skin disinfectant for central line insertion?

Accepted Answer

Chlorhexidine

Answer

Alcohol

Answer

Cetrimide

Answer

Povidone iodine

Question 3

Which of the following is not used as treatment for lymphatic filariasis -

Accepted Answer

Praziquantel

Answer

DEC

Answer

Albendazole

Answer

Ivermectin

Question 4

What is the primary reason for using a combination of four drugs in Anti-Koch's Treatment (AKT) for tuberculosis?

Accepted Answer

To decrease the risk of resistance due to mutation.

Answer

To decrease the risk of resistance due to conjugation.

Answer

To enhance overall treatment efficacy.

Answer

To simplify treatment.

Question 5

All are true about ciprofloxacin except?

Accepted Answer

More active at acidic pH

Answer

DNA gyrase inhibition

Answer

Contraindicated in pregnancy

Answer

Second generation fluoroquinolone

Question 6

As per RNTCP guidelines, Multi drug resistance (MDR) TB is defined as resistance to:

Accepted Answer

Rifampicin and isoniazid

Answer

Rifampicin

Answer

Rifampicin, isoniazid and ethambutol

Answer

None of the above

Question 7

Which sulphonamide has the longest acting duration?

Accepted Answer

Sulphadoxine

Answer

Sulfadiazine

Answer

Sulfamethoxazole

Answer

Sulfamethiazole

Question 8

Which antibiotic is Actinomycosis sensitive to?

Accepted Answer

Penicillin

Answer

Streptomycin

Answer

Nystatin

Answer

Doxycycline

Question 9

Which type of vaccine is used for chicken pox?

Accepted Answer

Live vaccine

Answer

Killed vaccine

Answer

Conjugated vaccine

Answer

Toxoid vaccine

Question 10

What is the mechanism of action of quinolones?

Accepted Answer

Inhibit DNA gyrase

Answer

Inhibit tetrahydrofolate reductase

Answer

Bind to 30S ribosomal subunit

Answer

Bind to bacterial cell membrane

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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