Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 671: Which of the following anti-tubercular drugs causes a flu-like syndrome?

A. Isoniazid
B. Ethambutol
C. Rifabutin
D. Rifampicin (Correct Answer)

Explanation: **Explanation:** The correct answer is **Rifampicin**. **Rifampicin** is a bactericidal drug that inhibits DNA-dependent RNA polymerase. The "flu-like syndrome" (characterized by fever, chills, headache, and malaise) is a classic immunological reaction associated with Rifampicin. It typically occurs when the drug is administered **intermittently** (less than twice weekly) or in high doses. This reaction is thought to be a Type II hypersensitivity response involving the formation of anti-rifampicin antibodies. **Analysis of Incorrect Options:** * **A. Isoniazid (INH):** The most characteristic side effects are peripheral neuropathy (due to Vitamin B6 deficiency) and hepatotoxicity. It does not cause a flu-like syndrome. * **B. Ethambutol:** Its hallmark toxicity is **optic neuritis**, leading to decreased visual acuity and red-green color blindness. It is bacteriostatic and does not cause systemic immunological syndromes like the one described. * **C. Rifabutin:** While a derivative of Rifamycin, it is primarily used in HIV patients due to fewer drug interactions. Its distinct side effect is **uveitis** and skin hyperpigmentation, but it is less commonly associated with the intermittent-dose flu-like syndrome compared to Rifampicin. **NEET-PG High-Yield Pearls:** * **Rifampicin** causes harmless **orange-red discoloration** of urine, sweat, and tears (important counseling point). * It is a potent **enzyme inducer** (CYP450), leading to many drug interactions (e.g., failure of oral contraceptives). * Other side effects of Rifampicin include the "4 P's": **P**urpura, **P**ruritus, **P**allor (hemolysis), and **P**roteinuria (rarely). * **Ethambutol** is the only primary anti-tubercular drug that is **bacteriostatic** and safe in pregnancy.

Question 672: What is a known side effect of zidovudine in patients with AIDS?

A. Megaloblastic anemia (Correct Answer)
B. Hyperuricemia
C. Nephrocalcinosis
D. Pancreatitis

Explanation: **Explanation:** **Zidovudine (AZT)** is a Nucleoside Reverse Transcriptase Inhibitor (NRTI) and was the first drug approved for HIV treatment. **Why Megaloblastic Anemia is correct:** Zidovudine acts as a thymidine analogue. Its primary dose-limiting toxicity is **bone marrow suppression**, specifically affecting the erythroid lineage. It interferes with DNA synthesis in red blood cell precursors, leading to macrocytosis and **megaloblastic anemia**. Interestingly, an increase in Mean Corpuscular Volume (MCV) is so characteristic of zidovudine therapy that it is often used as a surrogate marker for patient compliance. **Why other options are incorrect:** * **B. Hyperuricemia:** This is classically associated with Pyrazinamide (anti-TB drug) or cytotoxic chemotherapy (Tumor Lysis Syndrome), not zidovudine. * **C. Nephrocalcinosis:** This involves calcium deposition in the renal parenchyma, often seen in hyperparathyroidism or distal renal tubular acidosis. Among HIV drugs, Indinavir (a Protease Inhibitor) is more likely to cause renal issues like nephrolithiasis. * **D. Pancreatitis:** While NRTIs as a class can cause mitochondrial toxicity, pancreatitis is specifically the "signature" side effect of **Didanosine (ddI)** and **Stavudine (d4T)**, rather than zidovudine. **High-Yield Clinical Pearls for NEET-PG:** 1. **Mnemonic for Zidovudine:** **Z**idovudine causes **A**nemia and **M**yopathy (**ZAM**). 2. **Lactic Acidosis:** All NRTIs can cause lactic acidosis and hepatic steatosis due to mitochondrial DNA polymerase-gamma inhibition. 3. **Pregnancy:** Zidovudine is a preferred drug for preventing vertical transmission (mother-to-child) of HIV during labor and to the newborn. 4. **Granulocytopenia:** Along with anemia, neutropenia is a common hematological side effect.

Question 673: Dapsone is used in the treatment of:

A. Malaria
B. Dermatitis herpetiformis (Correct Answer)
C. Tuberculosis
D. Kala-azar

Explanation: **Dapsone (Diaminodiphenyl sulfone)** is the mainstay of treatment for **Dermatitis herpetiformis (DH)**, a chronic autoimmune blistering skin condition associated with celiac disease [3]. Dapsone works in DH by inhibiting the migration and function of neutrophils and suppressing the release of lysosomal enzymes [1], which rapidly resolves the characteristic pruritic vesicles. **Analysis of Options:** * **Dermatitis herpetiformis (Correct):** Dapsone is the drug of choice [3]. It provides dramatic symptomatic relief, often within 24–48 hours, though it does not treat the underlying gluten sensitivity. * **Malaria (Incorrect):** While Dapsone has antimalarial properties (inhibiting dihydropteroate synthase) [1, 5], it is not used alone. It was previously used in combination with pyrimethamine (Maloprim), but this is no longer a first-line treatment due to resistance and toxicity [5]. * **Tuberculosis (Incorrect):** Dapsone is a sulfone used for **Leprosy** (as part of MDT) [1, 2, 3, 4], not Tuberculosis. TB is treated with RIPE therapy (Rifampin, Isoniazid, Pyrazinamide, Ethambutol). * **Kala-azar (Incorrect):** Visceral leishmaniasis is treated with Liposomal Amphotericin B (drug of choice), Miltefosine, or Paromomycin. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Competitive inhibitor of dihydropteroate synthase (DHPS), inhibiting folic acid synthesis [5]. * **Leprosy:** Dapsone is a core component of WHO Multi-Drug Therapy (MDT) for both paucibacillary and multibacillary leprosy [4]. * **Side Effects:** 1. **Hemolysis:** Most common side effect; occurs especially in **G6PD deficient** patients (Screening is mandatory) [2, 3]. 2. **Methemoglobinemia:** Presents with cyanosis [2, 3]. 3. **Dapsone Syndrome:** A severe hypersensitivity reaction (fever, exfoliative dermatitis, lymphadenopathy, and hepatitis) occurring 4–6 weeks after starting therapy. * **Pneumocystis jirovecii:** Dapsone is used as a second-line prophylaxis in HIV patients allergic to Cotrimoxazole.

Question 674: Which among the following antimicrobial agents is available only in intravenous form?

A. Vancomycin
B. Meropenem (Correct Answer)
C. Streptomycin
D. All of the above

Explanation: **Explanation:** The correct answer is **Meropenem**. The route of administration for antimicrobials is determined by their chemical stability, gastrointestinal absorption (bioavailability), and intended clinical use. **1. Why Meropenem is the correct answer:** Meropenem belongs to the **Carbapenem** class of beta-lactams. Due to its chemical structure, it is not absorbed from the gastrointestinal tract and is susceptible to gastric acid degradation. Therefore, it must be administered parenterally. Unlike some other carbapenems (like Ertapenem, which can be given IM), Meropenem is specifically administered **only via the Intravenous (IV) route** to achieve the rapid, high plasma concentrations required for treating life-threatening nosocomial infections. **2. Why the other options are incorrect:** * **Vancomycin:** While primarily used IV for systemic infections (e.g., MRSA), it is available in **Oral form**. Crucially, oral Vancomycin is not absorbed systemically and is used specifically to treat *Clostridioides difficile* associated diarrhea. * **Streptomycin:** This aminoglycoside is administered via the **Intramuscular (IM) route** (and occasionally IV). It is a mainstay in the treatment of Tuberculosis and Plague but is not restricted to IV-only use. **High-Yield Clinical Pearls for NEET-PG:** * **Carbapenems:** All carbapenems (Imipenem, Meropenem, Doripenem, Ertapenem) are parenteral. Meropenem is preferred over Imipenem in meningitis because it has a **lower risk of causing seizures**. * **Oral Vancomycin:** Always remember—Oral = Local action (C. diff); IV = Systemic action (MRSA). * **IV-only drugs:** Other notable examples include **Daptomycin** and **Tigecycline**.

Question 675: Which is the most suitable tetracycline for use in a patient with impaired renal function?

A. Tetracycline
B. Demeclocycline
C. Oxytetracycline
D. Doxycycline (Correct Answer)

Explanation: **Explanation:** The correct answer is **Doxycycline**. **Why Doxycycline is the correct choice:** Most tetracyclines are primarily excreted by the kidneys via glomerular filtration. In patients with renal impairment, these drugs accumulate, leading to increased toxicity (including an anti-anabolic effect that raises blood urea nitrogen). **Doxycycline** (and to a lesser extent, Minocycline) is the exception. It is primarily excreted through the **bile into the feces** (enterohepatic circulation is not significant for its clearance). Because its elimination is independent of renal function, it does not accumulate in kidney failure, making it the safest tetracycline for such patients. No dose adjustment is required. **Analysis of Incorrect Options:** * **A. Tetracycline & C. Oxytetracycline:** These are older, short-acting tetracyclines that are highly dependent on renal excretion. They are contraindicated in renal failure as they can cause significant azotemia. * **B. Demeclocycline:** This intermediate-acting tetracycline is also renally excreted. Notably, it is known to cause nephrogenic diabetes insipidus and is clinically used to treat SIADH, but it is not suitable for patients with pre-existing renal impairment. **High-Yield Clinical Pearls for NEET-PG:** * **Safe in Renal Failure:** Remember the mnemonic **"D"** for Doxycycline = **"D"**umped in the feces. * **Anti-anabolic effect:** Tetracyclines (except Doxycycline) inhibit protein synthesis, which increases the nitrogen load on the kidneys, worsening uremia. * **Phototoxicity:** Demeclocycline carries the highest risk of phototoxicity among tetracyclines. * **Drug of Choice:** Doxycycline is the first-line treatment for Rickettsial infections, Chlamydia, and Cholera.

Question 676: Which of the following statements about levamisole is FALSE?

A. It acts as an immunostimulator.
B. It acts as an immunodepressor in high doses.
C. A single dose is sufficient for the treatment of psoriasis. (Correct Answer)
D. It acts as an antihelminthic by causing depolarization.

Explanation: **Explanation** Levamisole is a synthetic imidazothiazole derivative traditionally used as an anthelmintic and an immunomodulator. **Why Option C is False:** Levamisole is **not** a first-line treatment for psoriasis, and a single dose is never sufficient. While it has been explored for its immunomodulatory effects in various dermatological conditions, psoriasis typically requires chronic management with topical agents, phototherapy, or systemic immunosuppressants (like methotrexate or biologics). Using levamisole for psoriasis is largely obsolete and clinically unsupported as a "single-dose" cure. **Analysis of Other Options:** * **Option A (Immunostimulator):** Levamisole restores cell-mediated immune function by stimulating T-cell activation and macrophage phagocytosis. It was historically used as an adjuvant in colorectal cancer and for nephrotic syndrome. * **Option B (Immunodepressor):** While primarily an immunostimulant, levamisole exhibits a "bell-shaped" dose-response curve. At very high or prolonged doses, it can paradoxically cause immunosuppression. * **Option C (Anthelmintic):** It acts as a nicotinic acetylcholine receptor agonist in nematode muscles, causing **persistent depolarization** and spastic paralysis, leading to the expulsion of worms (especially *Ascaris lumbricoides*). **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Levamisole is highly effective for Ascariasis (Roundworm). [1] * **Adverse Effect:** A critical side effect to remember is **agranulocytosis** (reversible upon discontinuation). * **Levamisole-induced Vasculopathy:** Often seen in cocaine users, as levamisole is a common adulterant; it presents with retiform purpura and necrosis of the ear lobes. * **Mechanism:** Ganglionic stimulant in worms $\rightarrow$ Depolarizing neuromuscular blockade. [1]

Question 677: Which drug is used in the treatment of Toxoplasmosis?

A. Pyrimethamine (Correct Answer)
B. Ribavirin
C. Ganciclovir
D. Tetracycline

Explanation: **Explanation:** **Pyrimethamine** is the drug of choice for the treatment of **Toxoplasmosis** (caused by *Toxoplasma gondii*). It is a dihydrofolate reductase (DHFR) inhibitor that prevents the synthesis of folic acid in the parasite. In clinical practice, it is almost always used in combination with **Sulfadiazine** (a dihydropteroate synthase inhibitor) to achieve sequential blockade of the folate pathway, resulting in a synergistic effect. **Analysis of Incorrect Options:** * **Ribavirin (B):** A broad-spectrum antiviral drug used primarily for Hepatitis C (in combination with Interferon) and Respiratory Syncytial Virus (RSV) in children. * **Ganciclovir (C):** An antiviral agent specifically used for Cytomegalovirus (CMV) infections, particularly CMV retinitis in immunocompromised patients. * **Tetracycline (D):** While some tetracyclines (like Minocycline) have minor anti-protozoal activity, they are not the standard treatment for Toxoplasmosis. Clindamycin is the preferred alternative if sulfonamides are not tolerated. **Clinical Pearls for NEET-PG:** 1. **Folinic Acid (Leucovorin) Supplementation:** When using Pyrimethamine, Leucovorin must be co-administered to prevent bone marrow suppression (megaloblastic anemia) in the host. 2. **Pregnancy:** Spiramycin is the drug of choice for acute toxoplasmosis in pregnancy to prevent fetal transmission. 3. **HIV/AIDS:** Toxoplasmosis is a common cause of "ring-enhancing lesions" on brain MRI in AIDS patients; prophylaxis (with TMP-SMX) is started when CD4 counts drop below 100 cells/μL.

Question 678: Which of the following statements regarding tetracycline is NOT true?

A. It is not teratogenic (Correct Answer)
B. It can cause tooth discoloration
C. It can result in superinfection
D. It can lead to pseudomembranous colitis

Explanation: **Explanation:** The correct answer is **A (It is not teratogenic)** because this statement is false. Tetracyclines are well-known **teratogenic** agents and are classified as FDA Pregnancy Category D. They readily cross the placenta and bind to calcium in fetal bones and teeth. 1. **Why Option A is the correct choice (The False Statement):** Tetracyclines cause **fetal toxicity**, specifically affecting the skeletal system. Exposure during pregnancy can lead to permanent discoloration of deciduous teeth and **hypoplasia of the enamel**. Furthermore, they can cause **inhibition of bone growth** (deformities) in the fetus. 2. **Why Option B is incorrect:** Tetracyclines have a high affinity for calcium. In children under 8 years of age, they deposit in the dentin and enamel, causing permanent **yellow-brown discoloration**. 3. **Why Option C is incorrect:** Tetracyclines are broad-spectrum antibiotics that significantly alter the normal protective flora of the gut. This disruption allows for the overgrowth of resistant organisms, leading to **superinfections** (e.g., Oral/Vaginal Candidiasis). 4. **Why Option D is incorrect:** By suppressing normal intestinal flora, tetracyclines (especially older ones) can allow *Clostridioides difficile* to proliferate, leading to **pseudomembranous colitis**. **High-Yield NEET-PG Pearls:** * **Fanconi Syndrome:** Expired tetracyclines cause proximal renal tubular acidosis due to degradation products (epitetracycline). * **Phototoxicity:** Demeclocycline and Doxycycline are most commonly associated with exaggerated sunburn reactions. * **Drug of Choice:** Doxycycline is the DOC for Rickettsial infections, Chlamydia, Cholera, and Brucellosis. * **Contraindications:** Avoid in pregnancy, lactation, and children <8 years old.

Question 679: A client is prescribed with Pentamidine IV for the treatment of Pneumocystis jirovecii pneumonia. Suddenly, the client develops a temperature of 101.5°F. Which of the following would this sign most likely indicate?

A. An overdosage of the medication.
B. The need for an additional dosage.
C. The client has developed another infection. (Correct Answer)
D. The client is experiencing the therapeutic effect of the medication.

Explanation: Explanation:1. Why Option C is Correct:*Pneumocystis jirovecii* pneumonia (PJP) is an opportunistic infection primarily seen in immunocompromised patients (e.g., HIV/AIDS with CD4 <200). Pentamidine is a potent antiprotozoal agent [1] used when first-line Trimethoprim-Sulfamethoxazole (TMP-SMX) is contraindicated. A sudden spike in temperature (101.5°F) during treatment is a clinical "red flag." In an immunocompromised host, a new fever often signifies a **secondary opportunistic infection** (bacterial, viral, or fungal) or a "superinfection" rather than a reaction to the drug itself. Pentamidine is more commonly associated with hypotension and hypoglycemia rather than drug-induced pyrexia.2. Why Other Options are Incorrect:* **Option A:** Pentamidine overdose typically manifests as severe hypotension, cardiac arrhythmias (QT prolongation), or acute renal failure, not isolated fever.* **Option B:** Fever is a sign of clinical change, not a marker of sub-therapeutic dosing. Increasing the dose without investigation could lead to severe toxicity.* **Option D:** Therapeutic effect in PJP is indicated by improved oxygenation (PaO2), decreased respiratory rate, and resolution of fever, not the onset of a new high-grade fever.3. NEET-PG High-Yield Pearls:* **Drug of Choice for PJP:** TMP-SMX (Prophylaxis and Treatment).* **Pentamidine Side Effects:** "The 3 Hypos" — **Hypo**tension (especially with rapid IV infusion), **Hypo**glycemia (due to pancreatic islet cell toxicity), and **Hypo**calcemia. It can also cause Nephrotoxicity and Pancreatitis.* **Clinical Tip:** Always monitor Blood Glucose and Blood Pressure in patients on Pentamidine.* **Alternative for PJP:** Atovaquone or Clindamycin + Primaquine.

Question 680: Enfuvirtide belongs to which class of drugs?

A. Fusion inhibitors (Correct Answer)
B. Protease inhibitors
C. Gp 120 inhibitors
D. Nucleotide reverse transcriptase inhibitors

Explanation: **Explanation:** **Enfuvirtide** is a synthetic peptide that acts as a **Fusion Inhibitor**, a unique class of antiretroviral therapy (ART). Its mechanism involves binding to the **gp41** subunit of the viral envelope glycoprotein. By binding to gp41, it prevents the conformational changes required for the fusion of the HIV viral envelope with the host CD4 cell membrane, thereby blocking viral entry. **Analysis of Options:** * **B. Protease Inhibitors (e.g., Ritonavir, Atazanavir):** These act at the final stage of the viral life cycle by inhibiting the protease enzyme, preventing the cleavage of polyproteins into mature, infectious virions. * **C. Gp 120 inhibitors (e.g., Fostemsavir):** While Enfuvirtide targets gp41, drugs like Fostemsavir target the gp120 subunit to prevent initial attachment. Maraviroc is another entry inhibitor, but it acts as a CCR5 antagonist. * **D. Nucleotide Reverse Transcriptase Inhibitors (e.g., Tenofovir):** These are prodrugs that compete with natural nucleotides to cause DNA chain termination during the conversion of viral RNA to DNA. **High-Yield Clinical Pearls for NEET-PG:** * **Route of Administration:** Enfuvirtide is the only ART administered **subcutaneously** (twice daily). * **Side Effects:** The most common side effect is **injection site reactions** (nodules, erythema), occurring in nearly 100% of patients. * **Indication:** It is typically reserved for "salvage therapy" in patients with multi-drug resistant HIV-1. * **Mnemonic:** En**fu**virtide = **Fu**sion inhibitor (targets gp**41**; think "41" looks like "FI" for Fusion Inhibition).

Practice by Chapter

Beta-Lactam Antibiotics

Practice Questions

Aminoglycosides

Practice Questions

Macrolides and Ketolides

Practice Questions

Tetracyclines

Practice Questions

Quinolones

Practice Questions

Sulfonamides and Trimethoprim

Practice Questions

Antimycobacterial Drugs

Practice Questions

Antifungal Agents

Practice Questions

Antiviral Drugs

Practice Questions

Antiparasitic Agents

Practice Questions

Principles of Antimicrobial Selection

Practice Questions

Antimicrobial Resistance

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