Antimicrobial Agents Practice Questions

Q: Prophylaxis is essential to prevent which vitamin deficiency in patients taking isoniazid?

Vitamin B6. ### Explanation **Correct Option: D (Vitamin B6 / Pyridoxine)** **Mechanism:** Isoniazid (INH) is a structural analog of pyridoxine. It causes Vitamin B6 deficiency through two primary mechanisms: 1. **Competitive Inhibition:** INH inhibits the enzyme **pyridoxine phosphokinase**, which is essential for converting pyridoxine into its active form, **pyridoxal-5-phosphate (PLP)**. 2. **Increased Excretion:** INH reacts with pyridoxine to form isoniazid-pyridoxal hydrazones, which are rapidly excreted in the urine. PLP is a vital cofactor for the synthesis of inhibitory neurotransmitters like **GABA**. A deficiency leads to **peripheral neuropathy** (paresthesia, numbness) and, in severe cases, seizures [1]. Therefore, prophylactic administration of **10–50 mg/day of Pyridoxine** is mandatory for patients on INH, especially those with risk factors like diabetes, alcoholism, or malnutrition [1]. **Why other options are incorrect:** * **A (Vitamin B1/Thiamine):** Deficiency causes Beriberi or Wernicke-Korsakoff syndrome; it is not specifically induced by INH. * **B (Vitamin B2/Riboflavin):** Deficiency leads to cheilosis and glossitis; it is not associated with anti-tubercular therapy. * **C (Vitamin B3/Niacin):** While INH can theoretically interfere with tryptophan-to-niacin conversion (potentially causing Pellagra), **Vitamin B6 deficiency** is the primary, most common, and clinically significant complication requiring routine prophylaxis. **High-Yield Clinical Pearls for NEET-PG:** * **Slow Acetylators:** Patients who are "slow acetylators" of INH are at a much higher risk of developing peripheral neuropathy [1]. * **Sideroblastic Anemia:** INH can also cause microcytic anemia because PLP is a cofactor for **ALA synthase**, the rate-limiting enzyme in heme synthesis. * **Treatment Dose:** While prophylaxis is 10–50 mg, the treatment dose for established INH-induced neuropathy is higher (100–200 mg/day).

Q: Which of the following fluoroquinolones is contraindicated in liver diseases?

Pefloxacin. **Explanation:** The correct answer is **Pefloxacin**. **1. Why Pefloxacin is the correct answer:** The primary factor determining whether a drug is contraindicated in liver disease is its route of metabolism and elimination. Most fluoroquinolones are predominantly excreted unchanged by the kidneys. However, **Pefloxacin** is a notable exception as it undergoes extensive **hepatic metabolism**. It is converted in the liver to its active metabolite, norfloxacin. In patients with hepatic insufficiency, the clearance of pefloxacin is significantly reduced, leading to toxic accumulation. Therefore, it is contraindicated or requires extreme caution/avoidance in liver disease. **2. Why the other options are incorrect:** * **Levofloxacin and Ofloxacin:** These are primarily excreted **unchanged in the urine** via glomerular filtration and active tubular secretion. They require dose adjustments in renal failure but are generally safe to use in patients with hepatic impairment. * **Lomefloxacin:** Similar to the above, it is predominantly eliminated by the **kidneys** and does not undergo significant hepatic metabolism. **3. High-Yield Clinical Pearls for NEET-PG:** * **Moxifloxacin:** Like Pefloxacin, it is also metabolized by the liver (glucuronide conjugation) and is the fluoroquinolone of choice in **renal failure** (no dose adjustment needed), but should be used cautiously in hepatic failure. * **Photosensitivity:** Lomefloxacin and Sparfloxacin have the highest incidence of phototoxicity among quinolones. * **QT Prolongation:** Sparfloxacin and Moxifloxacin are most commonly associated with this adverse effect. * **Rule of Thumb:** If a drug is "Hepatically metabolized," adjust for liver disease; if "Renally excreted," adjust for CKD. Pefloxacin = Liver; Ofloxacin/Levofloxacin = Kidney.

Q: Doxycycline is used in the treatment of which of the following diseases?

All of the above. Doxycycline is a broad-spectrum bacteriostatic antibiotic belonging to the Tetracycline class [1]. It is highly lipid-soluble, allowing it to penetrate tissues and intracellular compartments effectively, making it the drug of choice for various atypical and zoonotic infections. **Why "All of the above" is correct:** * **Leptospirosis:** Doxycycline is used for both the treatment (mild cases) and **prophylaxis** of Leptospirosis in endemic areas. * **Q Fever:** Caused by *Coxiella burnetii*, Doxycycline is the first-line treatment for acute Q fever. * **Borreliosis:** This includes **Lyme disease** (*Borrelia burgdorferi*) and **Relapsing fever** (*Borrelia recurrentis*). Doxycycline is the gold standard treatment for these conditions [3]. **Clinical Pearls for NEET-PG:** 1. **Drug of Choice (DOC):** Doxycycline is the DOC for Rickettsial infections (Scrub typhus, Rocky Mountain Spotted Fever), Chlamydial infections (LGV, Trachoma, Psittacosis), Cholera, and Brucellosis (in combination with Rifampicin) [3]. 2. **Pharmacokinetics:** Unlike other tetracyclines, Doxycycline is primarily excreted via **bile** in the feces [3]. Therefore, it is the **safest tetracycline in patients with renal failure**. 3. **Adverse Effects:** It can cause esophageal ulceration (should be taken with plenty of water in an upright position), phototoxicity, and secondary infections (Candidiasis) [3]. 4. **Contraindications:** It should be avoided in pregnancy and children under 8 years due to the risk of permanent tooth discoloration and bone growth suppression [2].

Q: Which drug can cause skin pigmentation and ichthyosis-like side effects?

Clofazimine. **Explanation:** **Clofazimine** is a phenazine dye used primarily in the treatment of multibacillary leprosy and lepra reactions (Type 2). The correct answer is B because of the drug’s unique pharmacokinetic profile: it is highly lipophilic and tends to accumulate in the reticuloendothelial system and skin. 1. **Why Clofazimine is correct:** Due to its nature as a dye, it causes a characteristic **reddish-brown discoloration** of the skin, conjunctiva, and bodily fluids. Furthermore, it interferes with lipid metabolism in the skin, leading to **ichthyosis** (acquired skin dryness and scaling), which is a classic board-exam association for this drug. 2. **Why other options are incorrect:** * **Rifampicin:** Known for causing **orange-red discoloration** of urine, sweat, and tears, but it does not cause ichthyosis or permanent skin pigmentation. * **Dapsone:** Most famous for causing **hemolysis** (especially in G6PD deficiency) and **Methemoglobinemia**. It can cause "Dapsone Syndrome" (exfoliative dermatitis), but not ichthyosis. * **Steroids:** These typically cause skin **atrophy**, striae, and acneiform eruptions, rather than pigmentation or scaling. **High-Yield Clinical Pearls for NEET-PG:** * **Clofazimine** has anti-inflammatory properties, making it useful in treating **Erythema Nodosum Leprosum (ENL)**. * It has a very long half-life (approx. 70 days). * **Gastrointestinal side effect:** It can cause segmental enteritis and bowel obstruction due to crystal deposition in mesenteric lymph nodes. * **Mnemonic:** Remember the **3 C's** of Clofazimine: **C**oloration (Red-brown), **C**rystals (GI issues), and **C**erosis (Ichthyosis/Dry skin).

Q: Which of the following aminoglycosides is not available for parenteral use?

Framycetin. **Explanation:** The correct answer is **Framycetin**. The underlying medical concept is **systemic toxicity**. Aminoglycosides are highly polar, polycationic compounds that are not absorbed from the GI tract and must be given parenterally for systemic infections. However, certain aminoglycosides are **too toxic for systemic (parenteral) administration** because they cause severe nephrotoxicity and ototoxicity. **Framycetin** (and Neomycin) belongs to this category. It is restricted to **topical use** (e.g., skin creams like Soframycin, ophthalmic drops, or ear drops) and occasionally oral use for gut sterilization, as it is not absorbed into the bloodstream. **Analysis of Incorrect Options:** * **Amikacin & Gentamycin:** These are the most commonly used parenteral aminoglycosides. They are the "workhorses" for treating serious aerobic Gram-negative infections, including septicemia and complicated UTIs. * **Sisomycin:** This is a natural aminoglycoside (derived from *Micromonospora inyoensis*) that is chemically similar to Gentamycin and is available for parenteral injection. **High-Yield Clinical Pearls for NEET-PG:** * **Neomycin & Framycetin:** Only topical/oral (not absorbed). Neomycin is used orally for **Hepatic Encephalopathy** to kill ammonia-producing bacteria. * **Streptomycin:** The first aminoglycoside; now primarily used for Tuberculosis and Plague. * **Spectinomycin:** Related to aminoglycosides; used as an alternative for **Gonorrhea** in penicillin-allergic patients. * **Side Effects:** All systemic aminoglycosides share the "Triple O" toxicity: **O**totoxicity (vestibular/cochlear), **N**ephrotoxicity (ATN), and **N**euromuscular blockade.

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

It is a third-generation cephalosporin.. **Explanation:** The correct answer is **B** because **Cefuroxime is a second-generation cephalosporin**, not a third-generation one. 1. **Why Option B is the correct choice (The False Statement):** Cephalosporins are classified into generations based on their spectrum of activity. Cefuroxime (along with Cefaclor and Cefoxitin) belongs to the **second generation**. Third-generation cephalosporins include drugs like Ceftriaxone, Cefotaxime, and Ceftazidime, which generally have enhanced activity against gram-negative bacteria and better CNS penetration. 2. **Analysis of Incorrect Options (True Statements):** * **Option A:** Like all beta-lactams, cefuroxime inhibits **cell wall synthesis** by binding to Penicillin-Binding Proteins (PBPs), preventing the cross-linking of peptidoglycan. * **Option C:** Cross-resistance can occur between penicillins and cephalosporins due to shared mechanisms, such as the production of certain **beta-lactamases** or alterations in PBPs. * **Option D:** Compared to first-generation cephalosporins (like Cephalexin), second-generation agents like cefuroxime have an **expanded gram-negative spectrum** (covering *H. influenzae*, *Enterobacter*, and *Neisseria* spp.) while retaining significant gram-positive activity. **High-Yield Clinical Pearls for NEET-PG:** * **Cefuroxime Axetil** is the oral prodrug; it is unique because its absorption increases when taken **after a meal**. * It is the only second-generation cephalosporin capable of reaching therapeutic concentrations in the **CSF**, though it is no longer the first line for meningitis. * **Mnemonic for 2nd Gen:** "The **FOX** (**Cefoxitin**) ate a **FUR**ry (**Cefuroxime**) **FAC**on (**Cefaclor**)."

Question 1

Which of the following drugs is contraindicated in pregnancy?

Accepted Answer

Primaquine

Answer

Chloroquine

Answer

Amodiaquine

Answer

Quinine

Question 2

Prophylaxis is essential to prevent which vitamin deficiency in patients taking isoniazid?

Accepted Answer

Vitamin B6

Answer

Vitamin B1

Answer

Vitamin B2

Answer

Vitamin B3

Question 3

Which of the following fluoroquinolones is contraindicated in liver diseases?

Accepted Answer

Pefloxacin

Answer

Levofloxacin

Answer

Ofloxacin

Answer

Lomefloxacin

Question 4

Doxycycline is used in the treatment of which of the following diseases?

Accepted Answer

All of the above

Answer

Leptospirosis

Answer

Q fever

Answer

Borreliosis

Question 5

What is the most important mechanism by which tetracycline antibiotics exert antimicrobial action?

Accepted Answer

They bind to 30S ribosomes and inhibit bacterial protein synthesis.

Answer

They interfere with DNA mediated RNA synthesis in bacteria.

Answer

They bind to 50S ribosomes and interfere with translocation of the growing peptide chain in the bacteria.

Answer

They chelate Ca2+ ions and alter the permeability of the bacterial cell membrane.

Question 6

What is the recommended treatment for lepromatous leprosy?

Accepted Answer

Rifampicin + Dapsone + Clofazimine

Answer

Rifampicin + Dapsone

Answer

Rifampicin + Clofazimine

Answer

Rifampicin + Ofloxacin + Minocycline

Question 7

Which drug can cause skin pigmentation and ichthyosis-like side effects?

Accepted Answer

Clofazimine

Answer

Rifampicin

Answer

Dapsone

Answer

Steroids

Question 8

Which of the following antimicrobial agents is bactericidal?

Accepted Answer

Cotrimoxazole

Answer

Sulfonamides

Answer

Erythromycin

Answer

Chloramphenicol

Question 9

Which of the following aminoglycosides is not available for parenteral use?

Accepted Answer

Framycetin

Answer

Sisomycin

Answer

Amikacin

Answer

Gentamycin

Question 10

Which of the following is NOT true about cefuroxime?

Accepted Answer

It is a third-generation cephalosporin.

Answer

It inhibits cell wall synthesis.

Answer

Some acquired resistance to cefuroxime is seen with penicillin.

Answer

It is more active against gram-negative organisms.

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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