Antimicrobial Agents Practice Questions

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).

Q: Which of the following antimicrobial agents is not bacteriostatic?

Vancomycin. ### Explanation **Core Concept:** Antimicrobial agents are classified based on their effect on bacteria: **Bacteriostatic** drugs inhibit growth and replication (requiring the host’s immune system to clear the infection), while **Bactericidal** drugs actively kill the bacteria. **Why Vancomycin is the Correct Answer:** **Vancomycin** is a glycopeptide antibiotic that inhibits bacterial cell wall synthesis by binding to the **D-Ala-D-Ala** terminus of nascent peptidoglycan chains. Like most cell wall synthesis inhibitors (e.g., Penicillins, Cephalosporins), it is **bactericidal**. It causes cell lysis, making it the only bactericidal agent among the options provided. **Analysis of Incorrect Options:** * **Linezolid (Option A):** An oxazolidinone that inhibits protein synthesis by binding to the 50S subunit (specifically preventing the formation of the 70S initiation complex). It is **bacteriostatic** against Staphylococci and Enterococci (though it shows bactericidal activity against *S. pneumoniae*). * **Clindamycin (Option B):** A lincosamide that inhibits protein synthesis by binding to the 50S ribosomal subunit. It is primarily **bacteriostatic**. * **Erythromycin (Option C):** A macrolide that inhibits protein synthesis at the 50S subunit. Macrolides are classic examples of **bacteriostatic** agents. **NEET-PG High-Yield Pearls:** * **Mnemonic for Bactericidal drugs:** "**V**ery **F**inely **P**en**C**illed **A**t **B**edside" (**V**ancomycin, **F**luoroquinolones, **P**enicillins, **C**ephalosporins, **A**minoglycosides, **B**acitracin). * **Exception:** Aminoglycosides are the only protein synthesis inhibitors that are primarily bactericidal. * **Clinical Note:** Vancomycin is the drug of choice for **MRSA**. Rapid IV infusion can cause "**Red Man Syndrome**" due to histamine release (not an allergy).

Q: Which anti-tuberculosis agent causes orange-colored urine?

Rifampicin. **Explanation:** **Rifampicin** is a semi-synthetic derivative of rifamycin and a key bactericidal drug in the DOTS regimen. The correct answer is Rifampicin because it is a **zwitterionic compound with a characteristic red-orange color**. After administration, it is excreted through urine, sweat, tears, and saliva, imparting a harmless **orange-red discoloration** to these body fluids. **Why the other options are incorrect:** * **Isoniazid (INH):** Its primary side effects are peripheral neuropathy (due to Vitamin B6 deficiency) and hepatotoxicity. It does not cause pigment changes in secretions. * **Streptomycin:** An aminoglycoside that primarily causes ototoxicity (vestibular damage) and nephrotoxicity. * **Pyrazinamide:** Known for causing hyperuricemia (leading to gouty arthritis) and hepatotoxicity, but it does not discolor urine. **Clinical Pearls for NEET-PG:** 1. **Patient Counseling:** Always advise patients starting Rifampicin about orange urine to prevent unnecessary anxiety and improve compliance. It can also permanently stain soft contact lenses. 2. **Mechanism of Action:** Rifampicin inhibits **DNA-dependent RNA polymerase**, thereby blocking bacterial RNA synthesis. 3. **Enzyme Induction:** Rifampicin is a potent **Cytochrome P450 inducer**, leading to significant drug interactions (e.g., reducing the efficacy of oral contraceptives and warfarin). 4. **Resistance:** Resistance develops rapidly if used as monotherapy due to mutations in the *rpoB* gene.

Q: What is the drug of choice for brucellosis?

Doxycycline. **Explanation:** **Brucellosis** is a zoonotic infection caused by *Brucella* species, which are facultative intracellular organisms. Effective treatment requires drugs with high intracellular penetration and a low risk of relapse. **Why Doxycycline is the Correct Answer:** **Doxycycline** is the backbone of brucellosis treatment. Due to its high lipid solubility, it achieves excellent intracellular concentrations, which is essential for eradicating the bacteria residing within macrophages. However, when used as monotherapy, relapse rates are high. Therefore, the **WHO-recommended regimen** (and the gold standard) is **Doxycycline (100 mg BID for 6 weeks) + Rifampin (600–900 mg/day for 6 weeks)**. Alternatively, Doxycycline can be combined with Streptomycin (IM for 2–3 weeks). **Why Other Options are Incorrect:** * **A. Chloramphenicol:** While it has good intracellular penetration, it is not a first-line agent due to the risk of bone marrow toxicity (aplastic anemia) and higher relapse rates compared to tetracyclines. * **B. Erythromycin:** Macrolides have poor *in vitro* activity against *Brucella* and are clinically ineffective for this condition. * **D. Cefuroxime:** Second-generation cephalosporins do not have the necessary intracellular reach or specific activity required to treat brucellosis. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Doxycycline + Rifampin (for 6 weeks). * **In Pregnancy/Children (<8 years):** Doxycycline is contraindicated. The DOC is **Trimethoprim-Sulfamethoxazole (TMP-SMZ) + Rifampin**. * **Neurobrucellosis/Endocarditis:** Requires a triple regimen (Doxycycline + Rifampin + Aminoglycoside/Ceftriaxone) for a prolonged duration (3–6 months). * **Common Presentation:** Undulant fever (fever that rises and falls like waves), profuse sweating, and hepatosplenomegaly.

Q: All of the following are used in the treatment of visceral leishmaniasis except:

Hydroxychloroquine. **Explanation:** Visceral Leishmaniasis (Kala-azar) is caused by *Leishmania donovani*. The correct answer is **Hydroxychloroquine**, as it is an antimalarial and immunomodulatory agent used in conditions like Malaria, SLE, and Rheumatoid Arthritis, but it has **no clinical efficacy** against *Leishmania* species. **Analysis of Options:** * **Miltefosine:** This is the **first and only oral drug** approved for visceral leishmaniasis. It acts by interfering with cell signaling pathways and membrane synthesis. It is highly effective but contraindicated in pregnancy due to teratogenicity. * **Paromomycin:** An aminoglycoside antibiotic that inhibits protein synthesis. It is used as an injectable treatment for Kala-azar and is known for being cost-effective, though it carries risks of ototoxicity and nephrotoxicity. * **Sitamaquine:** An oral 8-aminoquinoline derivative (currently under investigation/limited use) that has shown efficacy against the visceral form of the disease by interfering with the parasite's mitochondrial function. **High-Yield NEET-PG Pearls:** 1. **Drug of Choice:** **Liposomal Amphotericin B** is currently the preferred treatment due to its high efficacy and low toxicity (single-dose regimen is often used in India). 2. **Miltefosine:** Must be avoided in pregnancy; female patients should use contraception for 5 months post-treatment. 3. **Sodium Stibogluconate (Pentavalent Antimonials):** Formerly the mainstay of treatment, but now largely abandoned in regions like Bihar, India, due to widespread resistance and cardiotoxicity (Q-T prolongation). 4. **Post-Kala-azar Dermal Leishmaniasis (PKDL):** Usually treated with prolonged courses of Miltefosine or Amphotericin B.

Q: Which of the following drug classes is known to cause nephrotoxicity?

Aminoglycosides. **Explanation:** **Aminoglycosides (Option B)** are the correct answer as they are notoriously associated with **dose-dependent nephrotoxicity**. The underlying mechanism involves the accumulation of the drug within the proximal convoluted tubule (PCT) cells. Aminoglycosides are filtered by the glomerulus and then reabsorbed by the tubular epithelium via the megalin-cubilin transport system. Once inside, they cause lysosomal rupture and oxidative stress, leading to **Acute Tubular Necrosis (ATN)**. This is typically reversible upon discontinuation of the drug. **Why other options are incorrect:** * **Doxycycline (Option A):** Unlike other tetracyclines, doxycycline is primarily excreted via the biliary route (feces), making it the safest tetracycline in patients with renal failure. It does not cause nephrotoxicity. * **Erythromycin (Option B):** This macrolide is primarily metabolized by the liver and excreted in bile. Its chief side effects are GI upset (motilin receptor agonism) and cholestatic hepatitis, not renal damage. * **Rifampicin (Option D):** While it can rarely cause interstitial nephritis, its hallmark side effects are hepatotoxicity and the harmless orange-red discoloration of body fluids. **High-Yield Clinical Pearls for NEET-PG:** 1. **Nephrotoxicity vs. Ototoxicity:** Aminoglycosides cause both. Neomycin is the most nephrotoxic; Streptomycin is the least. 2. **Monitoring:** To minimize toxicity, **Once-Daily Dosing** (Extended Interval Dosing) is preferred due to the "Post-Antibiotic Effect." 3. **Drug Interactions:** Risk of nephrotoxicity increases when aminoglycosides are co-administered with Loop Diuretics (e.g., Furosemide), Vancomycin, or Cisplatin. 4. **Rule of Thumb:** Aminoglycosides are "Mean" (NEphrotoxic and Ototoxic).

Q: What is the treatment of choice for benign tertian malaria?

Chloroquine. **Explanation:** **Benign tertian malaria** is caused by *Plasmodium vivax* and *Plasmodium ovale*. The standard treatment of choice for these species remains **Chloroquine**, as it is highly effective against the erythrocytic stages of the parasite in most regions. 1. **Why Chloroquine is Correct:** Chloroquine is a 4-aminoquinoline that concentrates in the acidic food vacuole of the parasite, inhibiting heme polymerase. This leads to the accumulation of toxic heme, killing the parasite. For *P. vivax* and *P. ovale*, it rapidly clears the fever and parasitemia. 2. **Why other options are incorrect:** * **Sulfamethoxazole-pyrimethamine (Option A):** Primarily used for chloroquine-resistant *P. falciparum*. It is not the first-line agent for benign tertian malaria due to slower action and increasing resistance. * **Quinine (Option B):** Reserved for severe or complicated malaria and chloroquine-resistant cases. It has a narrow therapeutic index and significant side effects (Cinchonism). * **Mefloquine (Option C):** Used for prophylaxis in travelers or as a second-line treatment for resistant *P. falciparum*. It is associated with neuropsychiatric side effects. **High-Yield Clinical Pearls for NEET-PG:** * **Radical Cure:** Chloroquine only treats the blood stages. To prevent relapse from dormant liver stages (**hypnozoites**), **Primaquine** must be administered for 14 days. * **G6PD Screening:** Always screen for G6PD deficiency before starting Primaquine to avoid acute hemolysis. * **Drug of Choice for Pregnancy:** Chloroquine is safe and remains the drug of choice for malaria in pregnancy (all trimesters) for sensitive strains. * **Malignant Tertian Malaria:** Refers to *P. falciparum*, which is typically treated with ACT (Artemisinin-based Combination Therapy).

Question 1

Which of the following drugs does NOT cause hemolysis?

Accepted Answer

Chloroquine

Answer

Primaquine

Answer

Nalidixic acid

Answer

Nitrofurantoin

Question 2

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

Accepted Answer

Tenofovir

Answer

Entecavir

Answer

Telbivudine

Answer

Lamivudine

Question 3

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 4

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

Accepted Answer

Rifampicin

Answer

Erythromycin

Answer

Penicillin

Answer

Cephalosporins

Question 5

Which of the following antimicrobial agents is not bacteriostatic?

Accepted Answer

Vancomycin

Answer

Linezolid

Answer

Clindamycin

Answer

Erythromycin

Question 6

Which anti-tuberculosis agent causes orange-colored urine?

Accepted Answer

Rifampicin

Answer

Isoniazid

Answer

Streptomycin

Answer

Pyrazinamide

Question 7

What is the drug of choice for brucellosis?

Accepted Answer

Doxycycline

Answer

Chloramphenicol

Answer

Erythromycin

Answer

Cefuroxime

Question 8

All of the following are used in the treatment of visceral leishmaniasis except:

Accepted Answer

Hydroxychloroquine

Answer

Sitamaquine

Answer

Paromomycin

Answer

Miltefosine

Question 9

Which of the following drug classes is known to cause nephrotoxicity?

Accepted Answer

Aminoglycosides

Answer

Doxycycline

Answer

Erythromycin

Answer

Rifampicin

Question 10

What is the treatment of choice for benign tertian malaria?

Accepted Answer

Chloroquine

Answer

Sulfamethoxazole-pyrimethamine

Answer

Quinine

Answer

Mefloquine

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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