Antimicrobial Agents Practice Questions

Q: Which of the following drugs is not used for prophylaxis against malaria?

Artesunate. Artesunate - **Artesunate** is a **fast-acting artemisinin derivative primarily used for treating acute malaria infections, especially severe or complicated cases**, and is not recommended for prophylaxis [4]. - Its short half-life and rapid clearance make it unsuitable for preventing malaria, as it would require frequent dosing, which is impractical for long-term prevention. *Doxycycline* - **Doxycycline** is an **antibiotic** that can be used for malaria prophylaxis, particularly in areas with **chloroquine-resistant P. falciparum** [1]. - It works by inhibiting protein synthesis in the parasite and must be taken daily, starting before travel and continuing for a period after returning [1]. *Chloroquine* - **Chloroquine** was historically a cornerstone for malaria prophylaxis due to its effectiveness and low cost, particularly in areas with **sensitive Plasmodium species.** [2] - However, widespread **chloroquine resistance**, especially in **P. falciparum**, has limited its current use for prophylaxis to specific regions where resistance is not prevalent [2]. *Mefloquine* - **Mefloquine** is an **antimalarial drug** commonly used for prophylaxis, especially in areas with **chloroquine-resistant P. falciparum** [2], [3]. - It is known for its convenience of once-weekly dosing but can have significant **neuropsychiatric side effects**, limiting its use in some individuals [3].

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: What is the recommended dosage for chloroquine chemoprophylaxis in malaria prevention?

500 mg once weekly. ***500 mg once weekly*** - The recommended dosage for chloroquine chemoprophylaxis in malaria prevention is **500 mg salt** (or equivalent to 300 mg base) administered **once weekly**. - This regimen ensures adequate blood concentrations to prevent malarial infection in endemic areas. *500 mg/week* - While the 500 mg dose is correct, simply stating "500 mg/week" without specifying "once weekly" could be misinterpreted. - Chloroquine is generally taken as a **single weekly dose**, not divided doses. *400 mg once weekly* - A dosage of **400 mg** is **sub-therapeutic** for weekly chloroquine chemoprophylaxis. - This dose would likely not provide sufficient protection against malaria. *500 mg BD/week* - Taking chloroquine **twice weekly (BD/week)** at 500 mg is excessive for chemoprophylaxis. - This regimen can lead to increased side effects and toxicity without providing additional prophylactic benefit.

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 primarily associated with Red man syndrome?

Vancomycin. **Vancomycin** - **Red man syndrome** is a well-known **infusion-related reaction** primarily associated with vancomycin. - It occurs due to the **rapid infusion** of vancomycin, leading to non-immunologic **mast cell degranulation** and histamine release. - Characterized by flushing, pruritus, and erythema of the upper body and face. - **Prevention:** Slow infusion rate (over 60 minutes or longer) and/or premedication with antihistamines. *Polymyxin B* - Polymyxin B is associated with **nephrotoxicity** and **neurotoxicity**, not typically with Red man syndrome. - It can cause **histamine release** leading to flushing and itching, but this is less common and less severe than with vancomycin. *Rifampicin* - Rifampicin is primarily known for causing **orange-red discoloration** of bodily fluids (e.g., urine, tears, sweat) and can cause **hepatotoxicity**, but not Red man syndrome. - It works by inhibiting bacterial **RNA synthesis** and is used to treat tuberculosis and other mycobacterial infections. *Teicoplanin* - Teicoplanin is a **glycopeptide antibiotic** similar to vancomycin, but it has a **significantly lower incidence** of Red man syndrome. - While it can cause some **infusion-related reactions**, they are generally milder and less frequent compared to vancomycin.

Q: Which of the following antibiotics is known to cause bleeding due to its effect on blood clotting?

Moxalactam. Moxalactam - Moxalactam is a **third-generation cephalosporin** known to cause **hypoprothrombinemia** and platelet dysfunction, leading to an increased risk of bleeding. - This effect is due to its **N-methylthiotetrazole (NMTT) side chain**, which inhibits vitamin K-dependent clotting factor synthesis. Cefaloridine - This is a **first-generation cephalosporin** that does not have the NMTT side chain and is not commonly associated with significant bleeding risks. - Its primary adverse effect of concern is **nephrotoxicity** at high doses, rather than coagulopathy. Ceftazidime - Ceftazidime is a **third-generation cephalosporin** primarily used for *Pseudomonas aeruginosa* infections but does **not contain the NMTT side chain** responsible for bleeding complications. - While broad-spectrum, it generally has a favorable safety profile concerning coagulation. *Cefazolin* - Cefazolin is a **first-generation cephalosporin** [1] widely used for surgical prophylaxis and skin infections [1], and it does **not interfere with coagulation** pathways. - Its main side effects are typical for penicillin-related antibiotics, such as hypersensitivity reactions [1],[2].

Q: Which of the following is a guanosine analogue?

Abacavir. ***Abacavir*** - **Abacavir** is a nucleoside reverse transcriptase inhibitor (NRTI) used in HIV treatment. - It is a **carbocyclic analogue of guanosine** (specifically, a 2'-deoxyguanosine analogue). - Structurally, it contains a modified cyclopentane ring instead of the ribose sugar, but retains the guanine base, making it a guanosine analogue. *Acyclovir* - **Acyclovir** is also a **guanosine analogue** - specifically an acyclic guanosine analogue. - It is an antiviral drug used to treat herpes simplex virus (HSV) and varicella-zoster virus (VZV) infections. - Note: Both Abacavir and Acyclovir are technically guanosine analogues; in this PYQ context, Abacavir is the expected answer. *Bromodeoxyuridine* - **Bromodeoxyuridine** is a **pyrimidine analogue**, specifically a thymidine analogue. - It is incorporated into DNA during replication and is used in research and as a radiosensitizer. *Allopurinol* - **Allopurinol** is a purine analogue (hypoxanthine analogue) that inhibits xanthine oxidase. - It is primarily used to treat **gout** and prevent kidney stones by reducing uric acid production. - While it's a purine derivative, it is not specifically a guanosine analogue.

Question 1

Which of the following drugs is not used for prophylaxis against malaria?

Accepted Answer

Artesunate

Answer

Doxycycline

Answer

Mefloquine

Answer

Chloroquine

Question 2

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 3

What is the recommended dosage for chloroquine chemoprophylaxis in malaria prevention?

Accepted Answer

500 mg once weekly

Answer

500 mg/week

Answer

400 mg once weekly

Answer

500 mg BD/week

Question 4

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 5

Which sulphonamide has the longest acting duration?

Accepted Answer

Sulphadoxine

Answer

Sulfadiazine

Answer

Sulfamethoxazole

Answer

Sulfamethiazole

Question 6

Which antibiotic is primarily associated with Red man syndrome?

Accepted Answer

Vancomycin

Answer

Polymyxin B

Answer

Rifampicin

Answer

Teicoplanin

Question 7

Which of the following antibiotics is known to cause bleeding due to its effect on blood clotting?

Accepted Answer

Moxalactam

Answer

Cefaloridine

Answer

Cefazolin

Answer

Ceftazidime

Question 8

Which of the following is a guanosine analogue?

Accepted Answer

Abacavir

Answer

Bromodeoxyuridine

Answer

Allopurinol

Answer

Acyclovir

Question 9

Which of the following statements about the biodisposition of penicillins and cephalosporins is NOT accurate?

Accepted Answer

Renal tubular reabsorption of beta-lactams is inhibited by probenecid

Answer

Procaine penicillin G is used for intramuscular injection

Answer

Nafcillin and ceftriaxone are eliminated mainly by biliary secretion

Answer

Oral bioavailability is affected by lability to gastric acid

Question 10

Amphotericin B toxicity can be lowered by:

Accepted Answer

Using Liposomal delivery systems

Answer

Reducing the dose

Answer

Combining with flucytosine

Answer

Administering with saline hydration

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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