Antimicrobial Agents Practice Questions

Q: What is the recommended dose of oseltamivir for a child aged 9 months?

3 mg/kg twice daily for 5 days. ***3 mg/kg twice daily for 5 days*** - For children aged **less than 1 year**, and weighing less than 15 kg, the recommended oseltamivir dose is **3 mg/kg** administered **twice daily** for 5 days. - This dosage regimen is effective in treating influenza and is based on studies of its **pharmacokinetics** and **efficacy** in this age group. *2 mg/kg twice daily for 5 days* - This dosage is **lower than recommended** for children under 1 year of age and may not achieve adequate therapeutic drug levels. - Subtherapeutic dosing could lead to **reduced antiviral efficacy** and potentially poorer clinical outcomes. *2.5 mg/kg twice daily for 5 days* - Similar to the 2 mg/kg dose, this is **below the standard recommendation** for infants and young children in this age bracket. - Inadequate dosing increases the risk of **treatment failure** and the development of **antiviral resistance**. *3.5 mg/kg twice daily for 5 days* - This dosage might be considered **higher than necessary** for a 9-month-old child and could potentially increase the risk of **adverse effects**. - While exact toxicities are rare within a reasonable range, adherence to recommended guidelines optimizes the **benefit-risk profile**.

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.

Q: A postoperative patient developed septicemia and was empirically started on combination chemotherapy by a new resident doctor. However, when the patient did not respond even after 10 days of antibiotic treatment, the review of the charts was done. It was found that the resident doctor had started the combination of antibiotics that was mutually antagonistic in action. Which of the following is the most likely combination that was given?

Ampicillin and Chloramphenicol. ***Ampicillin and Chloramphenicol*** - **Ampicillin** is a **bactericidal** antibiotic that inhibits cell wall synthesis, while **chloramphenicol** is **bacteriostatic** and inhibits protein synthesis. - When combined, the bacteriostatic action of chloramphenicol can antagonize the antimicrobial effect of ampicillin, particularly in infections where rapid bacterial killing is crucial. *Vancomycin and Amikacin* - **Vancomycin** is **bactericidal** (cell wall synthesis inhibitor), and **amikacin** is also **bactericidal** (aminoglycoside, protein synthesis inhibitor). - This combination is generally considered synergistic or additive, especially against gram-positive organisms and certain gram-negative bacteria, rather than antagonistic. *Cephalexin and Gentamicin* - Both **cephalexin** (a cephalosporin) and **gentamicin** (an aminoglycoside) are **bactericidal** antibiotics. - This combination can be synergistic, particularly against gram-negative bacteria, by targeting different bacterial processes (cell wall synthesis and protein synthesis, respectively). *Ciprofloxacin and Piperacillin* - **Ciprofloxacin** (a fluoroquinolone) and **piperacillin** (a penicillin) are both **bactericidal** antibiotics. - This combination is often used empirically to broaden coverage against a wide range of bacteria, exhibiting additive or synergistic effects, and is not typically antagonistic.

Q: In a child admitted with Haemophilus influenzae meningitis, cefotaxime was started instead of ampicillin. Which of the following is the likely reason for this?

H. influenzae strains known to produce Beta lactamase. ***H. influenzae strains known to produce Beta lactamase*** - Many *H. influenzae* strains, particularly in meningitis, produce **beta-lactamase enzymes** that inactivate ampicillin. - **Cefotaxime**, a third-generation cephalosporin, is **stable against beta-lactamases**, making it an effective empirical treatment. *Easier to give* - The route and ease of administration are generally **not the primary factors** in choosing between ampicillin and cefotaxime in a severe infection like meningitis. - Both medications can be administered intravenously, which is standard for meningitis treatment. *It is cheap* - While cost is a consideration in healthcare, **efficacy and clinical outcome** for a life-threatening condition like meningitis take precedence over cost. - Treatment choices are primarily driven by **antimicrobial susceptibility patterns** and patient safety. *H. influenzae strains known to have altered penicillin binding protein* - While **altered penicillin-binding proteins (PBPs)** can lead to resistance in some bacteria (e.g., *Streptococcus pneumoniae*), it is **not the predominant mechanism of resistance** to ampicillin in *H. influenzae*. - **Beta-lactamase production** is the much more common and significant reason for ampicillin resistance in *H. influenzae*.

Q: Which of the following is used in the prophylaxis of meningococcus?

Rifampicin. ***Rifampicin*** - **Rifampicin** is a recommended agent for **chemoprophylaxis** against **meningococcal disease**, especially for close contacts of patients. - It works by eliminating the carriage of *Neisseria meningitidis* in the **nasopharynx**. *Erythromycin* - **Erythromycin** is a **macrolide antibiotic** primarily used for respiratory tract infections and certain skin infections. - It is **not effective** for the prophylaxis of meningococcal disease due to poor penetration into the nasopharynx and varied efficacy against *N. meningitidis*. *Tetracycline* - **Tetracyclines** are broad-spectrum antibiotics, but they are **not typically used** for meningococcal prophylaxis. Resistance is common [1], and other agents are preferred due to better efficacy and lower risk of side effects in this context. *Penicillin* - **Penicillin** is effective for treating **active meningococcal infection** but is **not suitable for prophylaxis**. - It does not consistently eradicate the carrier state of *N. meningitidis* from the nasopharynx, which is essential for prophylaxis.

Q: What is the recommended duration of erythromycin for the treatment of diphtheria?

14 days. ***14 days*** - The recommended duration for **erythromycin** in treating diphtheria is **14 days** to ensure eradication of *Corynebacterium diphtheriae* and prevent toxin production. - This duration helps to eliminate the carrier state and reduce the risk of transmission to others. *3 days* - A 3-day course of antibiotics is **insufficient** for the complete eradication of *Corynebacterium diphtheriae* in diphtheria. - Such a short duration would likely lead to **treatment failure** and persistence of the infection. *7 days* - While 7 days is a common antibiotic duration for some infections, it is generally considered **too short** for diphtheria treatment. - A 7-day course may not fully eliminate the bacteria, potentially leading to **relapse** or a prolonged carrier state. *30 days* - A 30-day course of erythromycin for diphtheria is **unnecessarily long** and could increase the risk of side effects and antibiotic resistance. - The goal is eradication without excessive drug exposure, which 14 days achieves effectively.

Q: On chronic use, linezolid leads to which of the following?

Thrombocytopenia. ***Thrombocytopenia*** - **Linezolid** is known to cause **myelosuppression**, particularly **thrombocytopenia**, with prolonged use (typically >2 weeks). - This adverse effect is usually **reversible** upon discontinuation of the drug. - This is the **most characteristic** and **dose-limiting** hematologic toxicity of chronic linezolid therapy. *Deranged LFT* - While **linezolid** can occasionally cause **elevated liver enzymes**, this is a **less common** adverse effect compared to myelosuppression. - **Thrombocytopenia** is far more characteristic of **chronic linezolid use** and is the primary concern requiring monitoring. - Hepatotoxicity with linezolid is typically mild and less dose-limiting than hematologic effects. *Nephrotoxicity* - **Linezolid** is generally considered to have a low risk of **nephrotoxicity** and does not typically cause significant kidney damage. - **Aminoglycosides** or **vancomycin** are examples of antibiotics more commonly associated with nephrotoxic effects. *Ototoxicity* - **Ototoxicity**, characterized by hearing loss or tinnitus, is not a common or recognized side effect of **linezolid** therapy. - This adverse effect is more frequently associated with drugs like **aminoglycosides** or high-dose **loop diuretics**.

Q: Which of the following antimalarials is a slow-acting schizonticide?

Pyrimethamine. ***Pyrimethamine***- Pyrimethamine is a **folate antagonist** [1, 2] that acts as a **slow-acting schizonticide** [1, 3], primarily inhibiting dihydrofolate reductase in the parasite [1].- Due to its slow onset [1], it is typically used in combination with other faster-acting antimalarials, such as sulfadoxine, for treatment or prophylaxis [1].*Artemether*- Artemether is an **artemisinin derivative**, known for its **rapid action** and potent effect against all erythrocytic stages of *Plasmodium falciparum*.- It is a **fast-acting schizonticide** that causes widespread damage to parasite membranes and proteins.*Mefloquine*- Mefloquine is an antimalarial drug recognized for its **long half-life** and efficacy against multidrug-resistant *Plasmodium falciparum*.- While effective, it is considered of **intermediate speed** compared to the rapid action of artemisinins or the very slow action of drugs like pyrimethamine.*Quinine*- Quinine is a **fast-acting schizonticide** that is effective against the asexual erythrocytic forms of *Plasmodium* parasites.- Although potent, its use is limited by potential adverse effects such as **cinchonism** and a short half-life requiring frequent dosing.

Question 1

What is the recommended dose of oseltamivir for a child aged 9 months?

Accepted Answer

3 mg/kg twice daily for 5 days

Answer

2 mg/kg twice daily for 5 days

Answer

2.5 mg/kg twice daily for 5 days

Answer

3.5 mg/kg twice daily for 5 days

Question 2

Which of the following is a guanosine analogue?

Accepted Answer

Abacavir

Answer

Bromodeoxyuridine

Answer

Allopurinol

Answer

Acyclovir

Question 3

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 4

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

Question 5

A postoperative patient developed septicemia and was empirically started on combination chemotherapy by a new resident doctor. However, when the patient did not respond even after 10 days of antibiotic treatment, the review of the charts was done. It was found that the resident doctor had started the combination of antibiotics that was mutually antagonistic in action. Which of the following is the most likely combination that was given?

Accepted Answer

Ampicillin and Chloramphenicol

Answer

Vancomycin and Amikacin

Answer

Cephalexin and Gentamicin

Answer

Ciprofloxacin and Piperacillin

Question 6

In a child admitted with Haemophilus influenzae meningitis, cefotaxime was started instead of ampicillin. Which of the following is the likely reason for this?

Accepted Answer

H. influenzae strains known to produce Beta lactamase

Answer

It is cheap

Answer

Easier to give

Answer

H. influenzae strains known to have altered penicillin binding protein

Question 7

Which of the following is used in the prophylaxis of meningococcus?

Accepted Answer

Rifampicin

Answer

Tetracycline

Answer

Erythromycin

Answer

Penicillin

Question 8

What is the recommended duration of erythromycin for the treatment of diphtheria?

Accepted Answer

14 days

Answer

3 days

Answer

7 days

Answer

30 days

Question 9

On chronic use, linezolid leads to which of the following?

Accepted Answer

Thrombocytopenia

Answer

Deranged LFT

Answer

Nephrotoxicity

Answer

Ototoxicity

Question 10

Which of the following antimalarials is a slow-acting schizonticide?

Accepted Answer

Pyrimethamine

Answer

Artemether

Answer

Mefloquine

Answer

Quinine

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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