Antimicrobial Agents Practice Questions

Q: Which antimicrobial agent is effective against ESBL-producing microorganisms?

Beta-lactam plus beta-lactamase inhibitor. Explanation: Extended-Spectrum Beta-Lactamases (ESBLs) are enzymes produced by certain bacteria (most commonly *E. coli* and *Klebsiella*) that mediate resistance by hydrolyzing the beta-lactam ring [2]. 1. Why Option A is Correct: ESBLs are typically inhibited by Beta-lactamase inhibitors (BLIs) such as Clavulanic acid, Sulbactam, and Tazobactam. Therefore, combinations like Piperacillin-Tazobactam or Cefoperazone-Sulbactam remain effective. However, note that Carbapenems (e.g., Meropenem) are clinically considered the "gold standard" treatment for serious ESBL infections [1]. 2. Why Options B, C, and D are Incorrect: * Ampicillin (B): ESBLs readily hydrolyze penicillins. * Ceftriaxone (C): By definition, ESBLs confer resistance to all 1st, 2nd, and 3rd generation cephalosporins (like Ceftriaxone and Ceftazidime) as well as 4th generation cephalosporins (Cefepime) [1][3]. * Aztreonam (D): ESBLs also hydrolyze Monobactams [1]. Aztreonam is only stable against Metallo-beta-lactamases (NDM-1), not ESBLs. High-Yield Clinical Pearls for NEET-PG: * The "Carbapenem Gap": While BLI combinations work *in vitro*, Carbapenems are the drugs of choice for ESBL-related urosepsis or bacteremia [1]. * Marker for ESBL: Resistance to Ceftazidime is often used as a laboratory screening marker for ESBL production. * Co-resistance: ESBL-producing organisms often carry genes for resistance to other classes, such as Fluoroquinolones and Aminoglycosides. * Exceptions: ESBLs do not hydrolyze Cephamycins (e.g., Cefoxitin, Cefotetan), though these are rarely used clinically for this purpose.

Q: What drug is associated with the following adverse drug reaction (ADR)?

Demeclocycline. ***Demeclocycline*** - A **tetracycline antibiotic** that causes **photosensitivity reactions** due to its ability to absorb UV light and generate reactive oxygen species in the skin. - The **phototoxic dermatitis** appears as sunburn-like lesions on **sun-exposed areas** such as face, neck, and hands. *Chloramphenicol* - Primary adverse effects include **bone marrow suppression** leading to aplastic anemia and **gray baby syndrome** in neonates. - **Not associated** with photosensitivity reactions; its toxicity is mainly hematological and hepatic. *Erythromycin* - Commonly causes **gastrointestinal upset** (nausea, vomiting, diarrhea) and **hepatotoxicity** with prolonged use. - **Photosensitivity** is not a recognized adverse effect of this macrolide antibiotic. *Daptomycin* - Major adverse effects include **myopathy** with elevated creatine kinase levels and **eosinophilic pneumonia**. - **No association** with photosensitivity; monitoring focuses on muscle toxicity and pulmonary symptoms.

Q: Which drug predisposes to pyloric stenosis in infants?

Erythromycin. **Explanation:** The correct answer is **Erythromycin**. **Why Erythromycin is correct:** Erythromycin, a macrolide antibiotic, is a known risk factor for **Infantile Hypertrophic Pyloric Stenosis (IHPS)**. The underlying mechanism involves its action as a **motilin receptor agonist**. Erythromycin mimics the action of the hormone motilin, which stimulates gastrointestinal motility. In neonates (especially those under 2 weeks of age), excessive stimulation of these receptors leads to strong, uncoordinated contractions of the pyloric antrum, eventually resulting in hypertrophy of the pyloric sphincter and gastric outlet obstruction. This risk is highest with oral erythromycin but has also been associated with maternal use during late pregnancy or breastfeeding. **Why the other options are incorrect:** * **Streptomycin:** An aminoglycoside primarily associated with **ototoxicity** (8th cranial nerve damage) and **nephrotoxicity**. In utero exposure can lead to congenital deafness. * **Tetracycline:** Known for causing **discoloration of teeth** and enamel hypoplasia in children due to its ability to chelate calcium. It also inhibits bone growth. * **Nitrofurantoin:** Primarily associated with **hemolytic anemia** in neonates if used near term, especially in those with G6PD deficiency, but it does not affect the pylorus. **Clinical Pearls for NEET-PG:** * **Azithromycin** also carries a risk of IHPS, though it is statistically lower than Erythromycin. * **Classic Presentation of IHPS:** Non-bilious, projectile vomiting in an infant (3–6 weeks old) with a palpable "olive-shaped" mass in the epigastrium. * **Metabolic Abnormality in IHPS:** Hypochloremic, hypokalemic metabolic alkalosis (due to loss of HCl from vomiting). * **Drug of choice for Gastroparesis:** Erythromycin is sometimes used off-label in adults to stimulate gastric emptying due to its prokinetic properties.

Q: Which of the following drugs does NOT cause hemolysis?

Chloroquine. ### Explanation The core concept behind this question is **Drug-Induced Hemolysis in G6PD Deficiency**. Glucose-6-Phosphate Dehydrogenase (G6PD) is an enzyme essential for maintaining levels of reduced glutathione, which protects red blood cells (RBCs) from oxidative stress. Drugs that act as oxidizing agents can cause hemoglobin to precipitate (forming Heinz bodies), leading to hemolysis in G6PD-deficient individuals. **Why Chloroquine is the correct answer:** While **Chloroquine** is an antimalarial, it is considered **safe** and does not typically cause hemolysis in G6PD-deficient patients at standard doses. It lacks the potent oxidizing potential required to trigger an erythrocyte crisis. **Analysis of Incorrect Options:** * **Primaquine (B):** This is the classic "textbook" trigger for G6PD-related hemolysis. It is an 8-aminoquinoline that generates significant reactive oxygen species (ROS). * **Nalidixic acid (C):** A first-generation quinolone antibiotic known to be a potent oxidizing agent capable of inducing hemolytic anemia. * **Nitrofurantoin (D):** Commonly used for UTIs, this drug is a well-documented oxidative stressor and is strictly contraindicated in patients with known G6PD deficiency. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for G6PD Triggers:** "**AAA**" – **A**ntimalarials (Primaquine), **A**ntibiotics (Sulfonamides, Nitrofurantoin, Quinolones), and **A**nalgesics (Aspirin - high dose). * **Other Triggers:** Fava beans (Favism), Dapsone, and infections (most common cause). * **Safe Alternatives:** Chloroquine, Quinine, and Paracetamol (at normal doses) are generally safe. * **Peripheral Smear Finding:** Look for **"Bite cells"** (degmacytes) and **Heinz bodies** (denatured hemoglobin).

Q: Renal toxicity, though generally negligible, is associated with which of the following medications?

Tenofovir. **Explanation:** **Tenofovir** (specifically Tenofovir Disoproxil Fumarate or TDF) is a Nucleotide Reverse Transcriptase Inhibitor (NRTI) used in the treatment of HIV and Hepatitis B. Its primary dose-limiting toxicity is **nephrotoxicity**, which typically manifests as **proximal renal tubular dysfunction (Fanconi Syndrome)**. 1. **Why Tenofovir is correct:** Tenofovir is actively transported into the proximal convoluted tubule cells by organic anion transporters (OAT1/3). Accumulation within these cells leads to mitochondrial DNA depletion and dysfunction. This results in impaired reabsorption of glucose, amino acids, uric acid, and phosphate, leading to proteinuria and, in severe cases, acute kidney injury or chronic kidney disease. 2. **Why other options are incorrect:** * **Entecavir:** It is a potent guanosine analogue for HBV. While it requires dose adjustment in renal impairment, it is not inherently nephrotoxic. * **Telbivudine:** This drug is primarily associated with **myopathy** and increased creatine kinase (CK) levels, rather than renal toxicity. * **Lamivudine:** It is generally well-tolerated. Its main side effects include headache and nausea; it does not cause direct renal damage. **High-Yield Clinical Pearls for NEET-PG:** * **Tenofovir Alafenamide (TAF):** A newer prodrug of Tenofovir that achieves higher intracellular concentrations with much lower plasma levels, significantly reducing the risk of renal toxicity and bone mineral density loss compared to TDF. * **Fanconi Syndrome Triad:** Look for phosphaturia (leading to osteomalacia), glycosuria (with normal blood sugar), and metabolic acidosis in a patient on Tenofovir. * **Monitoring:** Patients on TDF should have their serum creatinine and phosphorus levels monitored regularly.

Q: What is the recommended prophylactic treatment for close contacts of meningococcal meningitis?

Rifampicin. **Explanation:** **1. Why Rifampicin is Correct:** Rifampicin is the drug of choice for the chemoprophylaxis of meningococcal meningitis. The goal of prophylaxis is to eradicate the nasopharyngeal carriage of *Neisseria meningitidis* in close contacts (e.g., household members, daycare contacts, or healthcare workers exposed to respiratory secretions). Rifampicin achieves high concentrations in salivary and respiratory secretions, effectively eliminating the carrier state and preventing secondary cases. The standard adult dose is 600 mg twice daily for 2 days. **2. Why the Other Options are Incorrect:** * **Erythromycin:** While a macrolide, it is not the standard of care for meningococcal prophylaxis as it is less effective at eradicating the nasopharyngeal carrier state compared to Rifampicin. * **Penicillin:** Although Penicillin G is the treatment of choice for the *active disease* (meningococcemia/meningitis), it does not reliably eliminate the nasopharyngeal carriage and therefore is not used for prophylaxis. * **Cephalosporins:** While 3rd generation cephalosporins (like Ceftriaxone) are used for treatment and can be used as an alternative for prophylaxis (via a single IM injection), they are not the primary first-line oral recommendation over Rifampicin in standard guidelines. **3. High-Yield Clinical Pearls for NEET-PG:** * **Alternative Prophylaxis:** If Rifampicin is contraindicated (e.g., pregnancy), **Ciprofloxacin** (500 mg single dose) or **Ceftriaxone** (250 mg IM single dose) are the preferred alternatives. * **Timing:** Prophylaxis should ideally be administered within 24 hours of identifying the index case. * **Side Effect Note:** Warn patients that Rifampicin may turn urine, sweat, and tears orange/red. * **Vaccination:** Chemoprophylaxis is necessary even if the contact has been previously vaccinated, as vaccines do not protect against all serogroups (especially Serogroup B).

Question 1

Which antimicrobial agent is effective against ESBL-producing microorganisms?

Accepted Answer

Beta-lactam plus beta-lactamase inhibitor

Answer

Ampicillin

Answer

Ceftriaxone

Answer

Aztreonam

Question 2

What drug is associated with the following adverse drug reaction (ADR)?

Accepted Answer

Demeclocycline

Answer

Chloramphenicol

Answer

Erythromycin

Answer

Daptomycin

Question 3

All of the following drugs are primarily bacteriostatic except?

Accepted Answer

Rifampicin

Answer

Sulphonamide

Answer

Chloramphenicol

Answer

Ethambutol

Question 4

Which class of antiretroviral drug is used for starting treatment for HIV infection?

Accepted Answer

Nucleoside Reverse Transcriptase Inhibitors (NRTIs)

Answer

Protease inhibitors

Answer

Fusion inhibitors

Answer

Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)

Question 5

Which drug predisposes to pyloric stenosis in infants?

Accepted Answer

Erythromycin

Answer

Streptomycin

Answer

Tetracycline

Answer

Nitrofurantoin

Question 6

Which of the following statements regarding amantadine and rimantadine is false?

Accepted Answer

Combination of amantadine and rimantadine are effective on Influenza B.

Answer

Rimantadine is 4-10 times more active than amantadine.

Answer

Both act by inhibiting an early step in viral replication.

Answer

They are effective against influenza A H1N1 if treatment is initiated within 2 days of the onset of symptoms.

Question 7

Which of the following drugs does NOT cause hemolysis?

Accepted Answer

Chloroquine

Answer

Primaquine

Answer

Nalidixic acid

Answer

Nitrofurantoin

Question 8

Renal toxicity, though generally negligible, is associated with which of the following medications?

Accepted Answer

Tenofovir

Answer

Entecavir

Answer

Telbivudine

Answer

Lamivudine

Question 9

A 45-year-old HIV-1 positive male was started on a cART regimen of Tenofovir-Emtricitabine-Efavirenz. After 9 months, he developed Efavirenz resistance, which led to failure of therapy. Which of the following drugs of the same class can be used in place of Efavirenz?

Accepted Answer

Etravirine

Answer

Delavirdine

Answer

Nelfinavir

Answer

Nevirapine

Question 10

What is the recommended prophylactic treatment for close contacts of meningococcal meningitis?

Accepted Answer

Rifampicin

Answer

Erythromycin

Answer

Penicillin

Answer

Cephalosporins

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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