Antimicrobial Agents Practice Questions

Q: Which of the following is NOT true about vancomycin?

Has 95% oral bioavailability. **Explanation:** **1. Why Option A is correct (The Concept):** Vancomycin is a large, complex glycopeptide molecule. Due to its high molecular weight and polar nature, it has **very poor oral bioavailability (<5%)**. It is not absorbed from the gastrointestinal tract into the systemic circulation. Therefore, the statement that it has 95% oral bioavailability is false. **2. Analysis of Incorrect Options:** * **Option B (Inhibits cell wall synthesis):** This is true. Vancomycin inhibits bacterial cell wall synthesis by binding to the **D-Ala-D-Ala** terminus of the nascent peptidoglycan pentapeptide, preventing cross-linking (transpeptidation). * **Option C (Parenteral and Oral use):** This is true. It is given **IV** for systemic infections (like endocarditis or pneumonia). It is given **orally** specifically for **Clostridioides difficile-associated diarrhea (CDAD)** because it remains in the gut lumen to act locally. * **Option D (Indicated for MRSA):** This is true. Vancomycin is the traditional "gold standard" treatment for Methicillin-resistant *Staphylococcus aureus* (MRSA) infections. **3. High-Yield Clinical Pearls for NEET-PG:** * **Red Man Syndrome:** An infusion-related reaction caused by histamine release; prevented by slowing the infusion rate. * **Spectrum:** Narrow spectrum; active **only** against Gram-positive bacteria. * **Resistance:** Mediated by the replacement of D-Ala-D-Ala with **D-Ala-D-Lac** (seen in VRSA/VRE). * **Adverse Effects:** Ototoxicity and Nephrotoxicity (especially when combined with aminoglycosides). * **Excretion:** Primarily via glomerular filtration; requires dose adjustment in renal failure.

Q: Which of the following groups of antibiotics is used in malaria?

Tetracyclines. **Explanation:** **Why Tetracyclines are the Correct Answer:** Tetracyclines (specifically **Doxycycline** and **Tetracycline**) and the related lincosamide **Clindamycin** possess potent antimalarial activity. They act by targeting the **apicoplast**, a non-photosynthetic plastid organelle in *Plasmodium* species that is essential for parasite survival. By inhibiting protein synthesis within this organelle, these drugs cause a "delayed death" effect, where the parasite survives the first division but fails to survive the second. Due to this slow onset of action, they are never used as monotherapy for acute malaria; instead, they are combined with fast-acting schizonticides like Quinine or Artesunate. **Why Other Options are Incorrect:** * **A. Aminoglycosides:** These inhibit the 30S bacterial ribosome and are primarily used for aerobic Gram-negative infections. They have no clinical role in treating malaria. * **C. Carbapenems:** These are broad-spectrum beta-lactams used for multi-drug resistant bacterial infections (e.g., ESBL producers). They target bacterial cell wall synthesis, which is absent in *Plasmodium*. * **D. Penicillins:** Like carbapenems, these target the peptidoglycan cell wall and are ineffective against protozoal parasites. **High-Yield Clinical Pearls for NEET-PG:** * **Doxycycline** is a first-line agent for **chemoprophylaxis** of malaria in areas with multi-drug resistant *P. falciparum*. * **Clindamycin** is the preferred alternative to Doxycycline for treating malaria in **pregnant women and children** (to avoid tetracycline-induced bone/teeth toxicity). * **Radical cure:** Refers to the eradication of hypnozoites (latent liver stages) of *P. vivax* and *P. ovale*, achieved only by **Primaquine** or **Tafenoquine**.

Q: Which drug is contraindicated in pregnancy?

Tetracycline. **Explanation:** **Tetracycline** is the correct answer because it is a known teratogen. It crosses the placenta and chelates calcium, leading to deposition in fetal bones and teeth. This results in **permanent yellowish-brown discoloration of teeth** and **enamel hypoplasia** if used after the 14th week of gestation. Additionally, it can cause **fetal growth retardation** and carries a high risk of **acute fatty liver necrosis** in the pregnant mother. **Analysis of Incorrect Options:** * **Erythromycin (Option B):** Generally considered safe in pregnancy (Category B). However, the *estolate* salt is avoided due to the risk of cholestatic hepatitis in the mother. * **Ampicillin (Option C):** Penicillins are the drugs of choice in pregnancy for various infections as they lack teratogenic potential. * **Chloroquine (Option D):** It is considered safe and is the drug of choice for treating malaria in pregnant women (except for resistant strains). **NEET-PG High-Yield Pearls:** * **SAFE Drugs in Pregnancy (Mnemonic: "PC-ME"):** **P**enicillins, **C**ephalosporins, **M**acrolides (except Clarithromycin), **E**rythromycin. * **CONTRAINDICATED Drugs (Mnemonic: "SAFE-T"):** **S**ulfonamides (Kernicterus), **A**minoglycosides (Ototoxicity), **F**luoroquinolones (Cartilage damage), **E**rythromycin estolate, **T**etracyclines (Teeth/Bone). * **Thalidomide:** Causes Phocomelia (seal-like limbs). * **Warfarin:** Causes Fetal Warfarin Syndrome (nasal hypoplasia, stippled epiphyses).

Q: Which antitubercular therapy (ATT) is most commonly implicated in causing peripheral neuropathy?

Isoniazid. ### Explanation **Correct Option: C. Isoniazid (INH)** **Mechanism of Neuropathy:** Isoniazid is the most common antitubercular drug to cause peripheral neuropathy. The underlying mechanism is a **functional deficiency of Pyridoxine (Vitamin B6)**. Isoniazid is chemically similar to pyridoxine; it inhibits the enzyme *pyridoxine phosphokinase*, which converts pyridoxine to its active form, pyridoxal phosphate. Furthermore, isoniazid reacts with pyridoxal phosphate to form a hydrazone complex that is rapidly excreted in the urine. This depletion leads to axonal degeneration of nerves, manifesting as "glove and stocking" paresthesia. **Why other options are incorrect:** * **A. Rifampicin:** Primarily known for its hepatotoxicity and for causing a harmless orange-red discoloration of body fluids (urine, sweat, tears). It is a potent microsomal enzyme inducer. * **B. Pyrazinamide:** Most commonly associated with hyperuricemia (which may precipitate gout) and hepatotoxicity. It does not typically affect peripheral nerves. * **D. Ethambutol:** Its hallmark side effect is **optic neuritis**, resulting in decreased visual acuity and red-green color blindness. It is generally not associated with peripheral neuropathy. **Clinical Pearls for NEET-PG:** * **Prophylaxis:** Peripheral neuropathy can be prevented by co-administering **Pyridoxine (10–25 mg/day)**. * **Risk Factors:** Slow acetylators, malnourished individuals, diabetics, alcoholics, and pregnant women are at a higher risk of INH-induced neuropathy. * **Treatment:** If neuropathy develops, the dose of Pyridoxine is increased to **100 mg/day**. * **Other INH Side Effects:** Hepatotoxicity (most common), Drug-induced Lupus (Anti-Histone antibodies), and Sideroblastic anemia.

Q: Which of the following tetracyclines has the potential to cause vestibular toxicity?

Minocycline. ### Explanation **Correct Option: A. Minocycline** Minocycline is the most lipid-soluble tetracycline. This high lipid solubility allows it to cross the blood-brain barrier and reach high concentrations in the endolymph of the inner ear and the vestibular apparatus. This accumulation leads to **vestibular toxicity**, manifesting as dizziness, ataxia, vertigo, nausea, and vomiting. These symptoms are more common in women and are usually reversible upon discontinuation of the drug. **Analysis of Incorrect Options:** * **B. Demeclocycline:** While it does not cause vestibular toxicity, it is notorious for causing **nephrogenic diabetes insipidus** (by inhibiting ADH action in the collecting duct) and severe **phototoxicity**. * **C. Doxycycline:** This is the most commonly used tetracycline due to its once-daily dosing and safety in renal failure (excreted via bile). It lacks the specific lipid profile required to cause significant vestibular side effects. * **D. Tetracycline:** This is a short-acting, older generation agent. It is primarily associated with gastrointestinal upset and teeth discoloration but does not penetrate the vestibular system significantly. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Doxycycline is the DOC for Rickettsial infections, Chlamydia, Cholera, and Brucellosis (with Rifampicin). * **Fanconi Syndrome:** Expired tetracyclines cause proximal renal tubular acidosis (Fanconi Syndrome). * **SIADH:** Demeclocycline is used therapeutically to treat SIADH because of its side effect profile. * **Contraindications:** Tetracyclines are contraindicated in pregnancy (teratogenic: causes bone growth retardation and tooth enamel hypoplasia) and in children under 8 years of age.

Q: Ganciclovir is more effective than acyclovir against which virus?

Cytomegalovirus (CMV). **Explanation:** The correct answer is **Cytomegalovirus (CMV)**. **1. Why Ganciclovir is more effective against CMV:** While both Ganciclovir and Acyclovir are nucleoside analogs that inhibit viral DNA polymerase, Ganciclovir is specifically designed with a higher affinity for the enzymes found in CMV. * **Mechanism:** In CMV-infected cells, Ganciclovir undergoes its initial phosphorylation by a specific viral protein kinase called **UL97**. This results in much higher intracellular concentrations of the active triphosphate form within CMV-infected cells compared to Acyclovir. * **Acyclovir Limitation:** Acyclovir requires the viral enzyme **Thymidine Kinase (TK)** for activation. CMV lacks TK, making Acyclovir significantly less potent against it. **2. Analysis of Incorrect Options:** * **Influenza virus:** This is an RNA virus. Both Ganciclovir and Acyclovir target DNA polymerase; therefore, they have no activity against Influenza. Influenza is treated with neuraminidase inhibitors (e.g., Oseltamivir). * **Herpes simplex virus (HSV):** While Ganciclovir is active against HSV, **Acyclovir** remains the drug of choice due to its superior safety profile and lower toxicity. Ganciclovir is reserved for CMV because of its significant side effects. **3. High-Yield NEET-PG Pearls:** * **Drug of Choice:** Ganciclovir is the drug of choice for **CMV Retinitis** and CMV prophylaxis in transplant patients. * **Dose-Limiting Toxicity:** The most important side effect of Ganciclovir is **Bone Marrow Suppression** (specifically neutropenia and thrombocytopenia). * **Valganciclovir:** This is the L-valyl ester prodrug of ganciclovir with high oral bioavailability. * **Resistance:** Resistance to Ganciclovir in CMV occurs due to mutations in the **UL97 gene**. In such cases, **Foscarnet** or **Cidofovir** (which do not require viral phosphorylation) are used.

Q: All the following cephalosporins have significant activity against Pseudomonas Species except?

Cefotaxime. **Explanation:** The core concept tested here is the spectrum of activity of different generations of Cephalosporins, specifically regarding **Pseudomonas aeruginosa**, a notorious Gram-negative pathogen. **Why Cefotaxime is the correct answer:** Cefotaxime is a **3rd generation cephalosporin**. While it has excellent activity against most Gram-negative bacteria (like *E. coli* and *Klebsiella*) and can cross the blood-brain barrier, it lacks significant activity against *Pseudomonas*. In the 3rd generation class, only a few specific drugs are "Anti-pseudomonal." **Analysis of Incorrect Options:** * **Ceftazidime (Option B):** This is a 3rd generation cephalosporin specifically designed for its potent activity against *Pseudomonas*. It is often considered the "gold standard" anti-pseudomonal cephalosporin. * **Cefoperazone (Option A):** Another 3rd generation cephalosporin with anti-pseudomonal activity. It is unique because it is primarily excreted via bile and does not require dose adjustment in renal failure. * **Cefepime (Option D):** This is a **4th generation cephalosporin**. 4th generation agents are characterized by an extended spectrum that covers both Gram-positive cocci and highly resistant Gram-negative organisms, including *Pseudomonas*. **High-Yield NEET-PG Pearls:** 1. **Anti-pseudomonal Cephalosporins:** Ceftazidime (3rd), Cefoperazone (3rd), Cefepime (4th), and Ceftobiprole (5th). 2. **Ceftriaxone vs. Cefotaxime:** Both are 3rd generation and neither covers *Pseudomonas*. 3. **Ceftaroline:** A 5th generation cephalosporin famous for **MRSA** coverage but, notably, it does **not** cover *Pseudomonas*. 4. **Mnemonic:** To remember anti-pseudomonal drugs, remember **"TAZ"** (Ceftazidime) and **"PIME"** (Cefepime).

Q: What is the drug of choice for the treatment of Trichomonas vaginalis?

Metronidazole. **Explanation:** **Correct Answer: D. Metronidazole** **Mechanism and Rationale:** Metronidazole is the drug of choice for *Trichomonas vaginalis*. It is a nitroimidazole prodrug that undergoes reductive activation by the enzyme **pyruvate:ferredoxin oxidoreductase (PFOR)** within anaerobic organisms. This process generates reactive nitro-radical intermediates that cause DNA strand breakage and inhibit protein synthesis, leading to cell death. While both Metronidazole and Tinidazole are effective, Metronidazole remains the standard first-line recommendation in most clinical guidelines. **Analysis of Incorrect Options:** * **A & C (Mebendazole and Albendazole):** These are **Benzimidazoles**, which act by inhibiting microtubule polymerization (binding to β-tubulin). They are anthelmintics used for intestinal nematodes (e.g., Ascaris, Hookworm) and have no activity against protozoa like *Trichomonas*. * **B (Tinidazole):** While Tinidazole is also highly effective against Trichomoniasis (often with fewer GI side effects and a longer half-life), Metronidazole is the traditional "textbook" drug of choice and the most frequently cited answer in standardized exams for this condition. **High-Yield Clinical Pearls for NEET-PG:** 1. **Disulfiram-like Reaction:** Patients must avoid alcohol during and for 48–72 hours after treatment with Metronidazole/Tinidazole due to inhibition of aldehyde dehydrogenase. 2. **Partner Treatment:** Trichomoniasis is a sexually transmitted infection (STI); **simultaneous treatment of the sexual partner** is mandatory to prevent "ping-pong" reinfection. 3. **Metallic Taste:** A common side effect of Metronidazole is a persistent metallic taste in the mouth. 4. **Pregnancy:** Metronidazole is considered safe for use in all trimesters of pregnancy for symptomatic Trichomoniasis.

Q: All of the following are adverse effects of aminoglycosides except?

Cholestatic jaundice. **Explanation:** Aminoglycosides (e.g., Gentamicin, Amikacin, Streptomycin) are potent bactericidal antibiotics that inhibit protein synthesis by binding to the 30S ribosomal subunit. Their adverse effect profile is a high-yield topic for NEET-PG. **Why Cholestatic Jaundice is the Correct Answer:** Aminoglycosides are primarily excreted unchanged by the kidneys and do not undergo significant hepatic metabolism. Therefore, they are not associated with hepatotoxicity or **cholestatic jaundice**. Cholestatic jaundice is a classic adverse effect associated with **Macrolides** (specifically Erythromycin estolate) and certain penicillins (like Cloxacillin). **Analysis of Incorrect Options:** * **Nephrotoxicity (A):** Aminoglycosides accumulate in the renal proximal tubular cells, leading to acute tubular necrosis (ATN). This is usually reversible and manifests as a rise in serum creatinine. Neomycin is the most nephrotoxic. * **Ototoxicity (B):** They cause irreversible damage to the 8th cranial nerve. This can be **vestibular** (vertigo, ataxia—common with Streptomycin/Gentamicin) or **cochlear** (hearing loss—common with Amikacin/Kanamycin). * **Neuromuscular Blockade (C):** Aminoglycosides inhibit the pre-junctional release of Acetylcholine and decrease post-junctional sensitivity. This can lead to apnea, especially if used with skeletal muscle relaxants. It is contraindicated in **Myasthenia Gravis**. **High-Yield Clinical Pearls for NEET-PG:** 1. **Mnemonic (3 N’s):** **N**ephrotoxicity, **N**euromuscular blockade, and **N**inth (8th) nerve damage. 2. **Teratogenicity:** They can cause fetal ototoxicity (Category D). 3. **Treatment of Toxicity:** Calcium gluconate or Neostigmine can reverse the neuromuscular blockade. 4. **Monitoring:** Therapeutic Drug Monitoring (TDM) is recommended due to a narrow therapeutic index.

Q: Which of the following antimalarial drugs is gameticidal for all species of Plasmodium?

Primaquine. **Explanation:** **Primaquine** is the correct answer because it is the only antimalarial drug that exhibits potent **gameticidal activity against all species of Plasmodium**, including *P. falciparum*. While many drugs can kill the gametocytes of *P. vivax* and *P. malariae*, *P. falciparum* gametocytes are notoriously resistant. Primaquine acts by generating reactive oxygen species (ROS) and interfering with the mitochondrial electron transport chain in the parasite, effectively preventing the transmission of malaria from humans to mosquitoes. **Analysis of Incorrect Options:** * **Quinine & Chloroquine:** These are primarily **blood schizonticides**. While they are gameticidal against *P. vivax* and *P. malariae*, they have **no effect** on the mature gametocytes of *P. falciparum*. * **Artesunate:** Artemisinin derivatives are potent blood schizonticides and do possess significant gameticidal activity against young/immature gametocytes. However, they are not as reliably effective against all stages of mature *P. falciparum* gametocytes as Primaquine. **High-Yield Clinical Pearls for NEET-PG:** 1. **Tissue Schizonticide:** Primaquine is also the drug of choice for the **radical cure** of *P. vivax* and *P. ovale* because it kills **hypnozoites** (latent liver stages), preventing relapse. 2. **G6PD Deficiency:** Before administering Primaquine, patients must be screened for G6PD deficiency. In these individuals, the drug causes oxidative stress leading to **acute hemolysis**. 3. **Pregnancy Contraindication:** Primaquine is contraindicated in pregnancy because the G6PD status of the fetus cannot be determined, risking fetal hemolysis. 4. **WHO Recommendation:** A single low dose of Primaquine (0.25 mg/kg) is recommended as a gameticide in *P. falciparum* malaria to reduce transmission in endemic areas.

Question 1

Which of the following is NOT true about vancomycin?

Accepted Answer

Has 95% oral bioavailability

Answer

Inhibits cell wall synthesis

Answer

Can be used parenterally as well as orally

Answer

Is indicated for MRSA infections

Question 2

Which of the following groups of antibiotics is used in malaria?

Accepted Answer

Tetracyclines

Answer

Aminoglycosides

Answer

Carbapenems

Answer

Penicillins

Question 3

Which drug is contraindicated in pregnancy?

Accepted Answer

Tetracycline

Answer

Erythromycin

Answer

Ampicillin

Answer

Chloroquine

Question 4

Which antitubercular therapy (ATT) is most commonly implicated in causing peripheral neuropathy?

Accepted Answer

Isoniazid

Answer

Rifampicin

Answer

Pyrazinamide

Answer

Ethambutol

Question 5

Which of the following tetracyclines has the potential to cause vestibular toxicity?

Accepted Answer

Minocycline

Answer

Demeclocycline

Answer

Doxycycline

Answer

Tetracycline

Question 6

Ganciclovir is more effective than acyclovir against which virus?

Accepted Answer

Cytomegalovirus (CMV)

Answer

Influenza virus

Answer

Herpes simplex virus

Answer

None of the above

Question 7

All the following cephalosporins have significant activity against Pseudomonas Species except?

Accepted Answer

Cefotaxime

Answer

Cefoperazone

Answer

Ceftazidime

Answer

Cefepime

Question 8

What is the drug of choice for the treatment of Trichomonas vaginalis?

Accepted Answer

Metronidazole

Answer

Mebendazole

Answer

Tinidazole

Answer

Albendazole

Question 9

All of the following are adverse effects of aminoglycosides except?

Accepted Answer

Cholestatic jaundice

Answer

Nephrotoxicity

Answer

Ototoxicity

Answer

Neuromuscular blockade

Question 10

Which of the following antimalarial drugs is gameticidal for all species of Plasmodium?

Accepted Answer

Primaquine

Answer

Quinine

Answer

Chloroquine

Answer

Artesunate

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

On this page

Practice by Chapter

Want unlimited practice?