Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 61: Which antitubercular drug causes gout?

A. Streptomycin
B. Ethambutol (Correct Answer)
C. Rifampicin
D. None

Explanation: ### Explanation **Correct Option: B. Ethambutol** Ethambutol is known to cause hyperuricemia, which can precipitate acute gouty arthritis. The underlying mechanism involves the inhibition of urate excretion by the renal tubules. Specifically, metabolites of ethambutol compete with uric acid for the organic anion transport system in the kidneys, leading to decreased clearance and elevated serum uric acid levels. *Note: While Pyrazinamide is the most common antitubercular drug associated with hyperuricemia, Ethambutol is a well-documented secondary cause among the first-line agents.* **Incorrect Options:** * **A. Streptomycin:** This is an aminoglycoside. Its primary adverse effects are ototoxicity (vestibulocochlear nerve damage) and nephrotoxicity. It does not affect uric acid metabolism. * **C. Rifampicin:** This drug is a potent enzyme inducer. Its hallmark side effects include orange-colored discoloration of body fluids (urine, sweat, tears) and hepatotoxicity. It is not associated with gout. **High-Yield Clinical Pearls for NEET-PG:** 1. **The "Gouty" Duo:** Both **Pyrazinamide** and **Ethambutol** cause hyperuricemia. If both are in the options, Pyrazinamide is usually the "more correct" or more potent cause, but Ethambutol is the correct choice here. 2. **Visual Side Effects:** Ethambutol’s most famous side effect is **Retrobulbar Neuritis**, leading to decreased visual acuity and red-green color blindness. It is generally avoided in young children who cannot undergo visual testing. 3. **Renal Adjustment:** Ethambutol is primarily excreted by the kidneys; therefore, the dose must be adjusted in patients with renal failure. 4. **Bacteriostatic vs. Bactericidal:** Ethambutol is the only **bacteriostatic** drug among the first-line ATT (Rifampicin, Isoniazid, and Pyrazinamide are bactericidal).

Question 62: A healthcare worker has a needle-stick injury exposure to HIV. Which of the following drug regimens is indicated for post-exposure prophylaxis?

A. Zidovudine + Lamivudine + Indinavir for 4 weeks (Correct Answer)
B. Zidovudine + Lamivudine + Nevirapine for 4 weeks
C. Zidovudine + Stavudine for 4 weeks
D. Zidovudine + Lamivudine for 4 weeks

Explanation: ### Explanation **Correct Option: A (Zidovudine + Lamivudine + Indinavir for 4 weeks)** Post-exposure prophylaxis (PEP) for HIV is categorized based on the severity of exposure. For **high-risk exposures** (e.g., deep needle-stick injuries with a high viral load source), an expanded regimen consisting of **three drugs** is indicated. The combination of two Nucleoside Reverse Transcriptase Inhibitors (NRTIs) like **Zidovudine and Lamivudine** plus a Protease Inhibitor (PI) like **Indinavir** (or Lopinavir/Ritonavir) is the classic recommendation to ensure maximum viral suppression. The duration of treatment is strictly **4 weeks (28 days)**. **Analysis of Incorrect Options:** * **Option B:** Nevirapine (an NNRTI) is contraindicated in PEP because it carries a high risk of severe hepatotoxicity and Stevens-Johnson Syndrome (SJS) in HIV-negative individuals. * **Option C:** Zidovudine and Stavudine should never be used together. Both are thymidine analogs that compete for the same phosphorylation pathway, leading to **pharmacological antagonism**. * **Option D:** This two-drug regimen (Basic Regimen) was previously used for low-risk exposures. However, current guidelines (WHO/NACO) now favor a three-drug regimen for all significant exposures to simplify protocols and increase efficacy. **High-Yield Clinical Pearls for NEET-PG:** * **Timing:** PEP should be started as soon as possible, ideally within **2 hours**, and definitely within **72 hours** of exposure. * **Current NACO/WHO Preferred Regimen:** Tenofovir (TDF) + Lamivudine (3TC) + Dolutegravir (DTG). * **Monitoring:** Baseline HIV testing should be done, followed by repeat testing at 6 weeks, 3 months, and 6 months. * **Zidovudine Side Effects:** Most common is anemia (bone marrow suppression) and GI intolerance.

Question 63: Metronidazole is indicated in the treatment of which one of the following conditions?

A. Traveller's diarrhea
B. Escherichia coli-induced diarrhoea
C. Cryptosporidium-induced diarrhea
D. Helicobacter pylori infection (Correct Answer)

Explanation: **Explanation:** **Metronidazole** is a nitroimidazole derivative that acts by forming reactive cytotoxic intermediates that cause DNA strand breakage. It is primarily effective against **obligate anaerobes** and certain **protozoa**. **1. Why Option D is Correct:** *Helicobacter pylori* is a microaerophilic, Gram-negative bacterium. Metronidazole is a core component of several multidrug regimens (such as the **Bismuth-based Quadruple Therapy** or the **Clarithromycin-based Triple Therapy**) used to eradicate *H. pylori*. It is particularly useful in patients allergic to penicillin or in regions where resistance patterns allow its use. **2. Why Other Options are Incorrect:** * **A & B (Traveller's Diarrhea / E. coli):** These are most commonly caused by Enterotoxigenic *E. coli* (ETEC). The drugs of choice are **Fluoroquinolones** (like Ciprofloxacin) or **Rifaximin**. Metronidazole has no activity against aerobic Gram-negative rods like *E. coli*. * **C (Cryptosporidium):** This protozoan causes self-limiting diarrhea in immunocompetent hosts but severe diarrhea in AIDS patients. The drug of choice is **Nitazoxanide**. Metronidazole is ineffective against *Cryptosporidium*. **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Metronidazole is the DOC for **Pseudomembranous colitis** (mild-to-moderate *C. difficile*), **Amoebiasis**, **Giardiasis**, **Trichomoniasis**, and **Bacterial Vaginosis**. * **Disulfiram-like Reaction:** Patients must avoid alcohol while on Metronidazole due to the inhibition of aldehyde dehydrogenase. * **Side Effects:** Metallic taste, nausea, and peripheral neuropathy (with long-term use). * **Mechanism:** It requires reductive activation of the nitro group by the enzyme **pyruvate:ferredoxin oxidoreductase (PFOR)**, found only in anaerobes.

Question 64: A 45-year-old man is placed on an antifungal agent for systemic infection and is noted to have decreased serum leukocyte and platelet counts. Bone marrow suppression is a common adverse effect of which of the following drugs?

A. Griseofulvin
B. Terbinafine
C. Fluconazole
D. Flucytosine (Correct Answer)

Explanation: **Explanation:** **Flucytosine (5-Fluorocytosine)** is the correct answer. It is a pyrimidine antimetabolite that acts as a prodrug. Inside the fungal cell, it is converted by the enzyme **cytosine deaminase** into **5-fluorouracil (5-FU)**, which inhibits DNA and protein synthesis. While human cells lack cytosine deaminase, the intestinal flora can convert some flucytosine into 5-FU systemically. This leads to significant **bone marrow suppression** (leukopenia, thrombocytopenia, and anemia), which is its most characteristic and dose-limiting adverse effect. **Analysis of Incorrect Options:** * **Griseofulvin (A):** Primarily used for dermatophytosis. Its common side effects include headaches, GI upset, and photosensitivity. It is an inducer of Cytochrome P450. * **Terbinafine (B):** An allylamine that inhibits squalene epoxidase. It is most commonly associated with GI distress, taste disturbances, and rarely, hepatotoxicity, but not typically bone marrow suppression. * **Fluconazole (C):** An azole that inhibits ergosterol synthesis. It is generally well-tolerated; its main concerns are GI upset and inhibition of CYP3A4 enzymes. **High-Yield Clinical Pearls for NEET-PG:** * **Synergy:** Flucytosine is almost always used in combination with **Amphotericin B** (especially for Cryptococcal meningitis) to prevent the rapid development of resistance. * **Mechanism:** It inhibits **thymidylate synthase**, thereby halting DNA synthesis. * **Monitoring:** Patients on Flucytosine require regular **Complete Blood Counts (CBC)** to monitor for hematological toxicity. * **Renal Impairment:** Toxicity is significantly increased in patients with renal failure, as the drug is excreted unchanged by the kidneys.

Question 65: Which one of the following is a nucleoside analog reverse transcriptase inhibitor?

A. Efavirenz
B. Nevirapine
C. Zidovudine (Correct Answer)
D. Saquinavir

Explanation: ### Explanation **Correct Answer: C. Zidovudine** **Mechanism of Action:** Zidovudine (AZT) is a **Nucleoside Reverse Transcriptase Inhibitor (NRTI)** [2]. It is a structural analog of thymidine [1]. To become active, it must undergo intracellular phosphorylation by host cell kinases into its triphosphate form [1, 2]. It then competes with natural nucleotides for incorporation into the viral DNA chain by the enzyme **Reverse Transcriptase** [1]. Once incorporated, it causes **premature chain termination** because it lacks the 3'-OH group necessary for forming a phosphodiester bond [1]. **Analysis of Incorrect Options:** * **A & B (Efavirenz and Nevirapine):** These are **Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)** [2]. Unlike NRTIs, they do not require phosphorylation and do not compete with nucleotides. Instead, they bind directly to a non-catalytic "pocket" on the Reverse Transcriptase enzyme, causing a conformational change that inhibits its activity. * **D (Saquinavir):** This is a **Protease Inhibitor (PI)**. It inhibits the viral protease enzyme (HIV-1 protease), preventing the cleavage of gag-pol polyproteins into functional mature proteins, resulting in the production of immature, non-infectious virions. **Clinical Pearls for NEET-PG:** * **Zidovudine Side Effects:** The most characteristic side effect is **bone marrow suppression** (anemia and neutropenia). It is also associated with **myopathy** and nail hyperpigmentation. * **Prevention of Mother-to-Child Transmission (PMTCT):** Zidovudine was the first drug used to reduce vertical transmission of HIV. * **Mitochondrial Toxicity:** NRTIs can inhibit mitochondrial DNA polymerase-gamma, leading to lactic acidosis and hepatic steatosis (Stavudine > Zidovudine) [1]. * **Tenofovir:** Note that Tenofovir is a **Nucleotide** analog (already has one phosphate group), whereas Zidovudine is a **Nucleoside** analog.

Question 66: Prolonged treatment with Isoniazid leads to deficiency of which vitamin?

A. Pyridoxine (Correct Answer)
B. Thiamine
C. Pantothenic acid
D. Niacin

Explanation: **Explanation:** **Mechanism of Pyridoxine (Vitamin B6) Deficiency:** Isoniazid (INH) is a structural analogue of Pyridoxine. It causes deficiency through two primary mechanisms: 1. **Inhibition of Pyridoxine Activation:** INH inhibits the enzyme *pyridoxine phosphokinase*, which converts pyridoxine into its active form, Pyridoxal-5-Phosphate (PLP). 2. **Increased Excretion:** INH reacts with PLP to form a hydrazone complex, which is rapidly excreted in the urine. Since PLP is a crucial cofactor for neurotransmitter synthesis (like GABA), its deficiency leads to **Peripheral Neuropathy**, characterized by paresthesia and numbness [1]. **Analysis of Incorrect Options:** * **B. Thiamine (B1):** Deficiency typically results from chronic alcoholism or malnutrition, leading to Beriberi or Wernicke-Korsakoff syndrome, not INH therapy. * **C. Pantothenic acid (B5):** Deficiency is extremely rare as it is ubiquitous in food; it is not associated with anti-tubercular drugs. * **D. Niacin (B3):** While INH can theoretically interfere with the conversion of Tryptophan to Niacin (potentially causing Pellagra), **Pyridoxine deficiency** is the primary, most common, and clinically significant side effect tested in exams. **Clinical Pearls for NEET-PG:** * **Prophylaxis:** To prevent neuropathy, Pyridoxine is co-administered with INH at a dose of **10–20 mg/day** [1]. * **Risk Groups:** Slow acetylators, diabetics, alcoholics, and malnourished patients are at higher risk of INH-induced neuropathy [1]. * **Sideroblastic Anemia:** Since PLP is a cofactor for ALA synthase (heme synthesis), INH can also cause microcytic sideroblastic anemia.

Question 67: Which of the following conditions is NOT typically treated with azoles?

A. Chromomycosis
B. Histoplasmosis
C. Paracoccidioidomycosis
D. Cryptococcal meningitis (Correct Answer)

Explanation: The correct answer is **Cryptococcal meningitis** because, while azoles (specifically Fluconazole) are used in the maintenance phase, they are **not** the treatment of choice for the induction phase of this life-threatening condition [1]. **1. Why Cryptococcal Meningitis is the correct answer:** The standard of care for the induction phase of Cryptococcal meningitis is a combination of **Amphotericin B and Flucytosine** [1]. Azoles are fungistatic and do not achieve rapid clearance of the fungus from the CSF. Although Fluconazole is used for long-term suppression (maintenance), it is insufficient as a primary treatment for the acute, severe stage of the disease [1]. **2. Why the other options are incorrect:** * **Chromomycosis:** Itraconazole is a first-line agent for this subcutaneous fungal infection, often combined with surgery or cryotherapy. * **Histoplasmosis:** Itraconazole is the drug of choice for mild-to-moderate cases [1]. Amphotericin B is reserved only for severe or disseminated disease. * **Paracoccidioidomycosis:** Itraconazole is considered the gold standard for treatment due to its high efficacy and lower toxicity compared to older sulfonamides. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC) for most systemic mycoses:** Itraconazole (e.g., Blastomycosis, Sporotrichosis, Histoplasmosis) [1]. * **Voriconazole:** DOC for **Invasive Aspergillosis** [3]. * **Fluconazole:** Notable for excellent CSF penetration [2], but its fungistatic nature limits its use in the induction phase of meningitis. * **Ketoconazole:** Now rarely used systemically due to its side effect profile (Cushing’s syndrome treatment, hepatotoxicity, and inhibition of steroidogenesis).

Question 68: Amphotericin B is used for the treatment of which of the following conditions?

A. Sleeping sickness
B. Kala azar (Correct Answer)
C. Malaria
D. Filaria

Explanation: **Explanation:** **Amphotericin B** is a potent polyene antifungal agent that also possesses significant antiprotozoal activity, particularly against *Leishmania donovani*, the causative agent of **Kala azar (Visceral Leishmaniasis)**. 1. **Why Kala azar is correct:** Amphotericin B acts by binding to ergosterol in the cell membrane of the parasite, creating pores that lead to ion leakage and cell death. While traditionally an antifungal, it is now considered the **drug of choice** for Kala azar in many regions (especially India) due to widespread resistance to Sodium Stibogluconate. **Liposomal Amphotericin B (L-AmB)** is preferred as it is less toxic and highly effective as a single-dose treatment. 2. **Why other options are incorrect:** * **Sleeping Sickness (African Trypanosomiasis):** Treated with Suramin, Pentamidine (early stage), or Melarsoprol and Nifurtimox-eflornithine combination (late stage). * **Malaria:** Treated with Chloroquine, Artemisinin-based Combination Therapy (ACT), or Quinine. * **Filaria:** Treated with Diethylcarbamazine (DEC), Ivermectin, or Albendazole. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Binds to **ergosterol** (fungal/protozoal) rather than cholesterol (human), though cross-reactivity causes its side effects. * **Side Effects:** Most famous for **nephrotoxicity** (causes distal Renal Tubular Acidosis), "shake and bake" reactions (fever/chills), and hypokalemia. * **Liposomal Formulations:** These reduce nephrotoxicity because the drug is sequestered in liposomes and delivered more specifically to the Reticuloendothelial System (liver/spleen), where the Leishmania parasites reside.

Question 69: Which drug is contraindicated in patients allergic to sulphonamides?

A. Brizolamide
B. Brimonidine
C. Zonisamide (Correct Answer)
D. Bimatoprost

Explanation: **Explanation:** The correct answer is **Zonisamide**. **Mechanism and Concept:** Sulphonamide allergy is a common clinical concern due to potential cross-reactivity between drugs containing a sulfonamide ($-SO_2NH_2$) moiety. **Zonisamide**, an antiepileptic drug used for focal seizures, is chemically classified as a sulfonamide. Therefore, it is contraindicated in patients with a known hypersensitivity to sulfonamides, as it can trigger severe allergic reactions, including Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN). **Analysis of Options:** * **Brizolamide (Option A):** While Brinzolamide is a carbonic anhydrase inhibitor and *is* a sulfonamide derivative, the question asks for the most definitive contraindication among the choices provided. However, in many clinical contexts, Zonisamide is more strictly highlighted in pharmacology textbooks regarding this specific contraindication. (Note: Brinzolamide is also technically contraindicated, but Zonisamide is a classic high-yield "non-antimicrobial sulfonamide" in NEET-PG). * **Brimonidine (Option B):** This is an alpha-2 adrenergic agonist used in glaucoma. It does not contain a sulfonamide group and is safe to use. * **Bimatoprost (Option D):** This is a prostaglandin analogue (PGF2α) used for glaucoma and eyelash hypotrichosis. It has no structural relation to sulfonamides. **High-Yield Clinical Pearls for NEET-PG:** * **Non-antimicrobial Sulfonamides:** Remember the mnemonic "Common Sulfonamides" – **C**elecoxib, **A**cetazolamide/Brinzolamide, **S**ulfonylureas (Glipizide), **T**hiazide diuretics, **L**oop diuretics (Furosemide), and **Z**onisamide. * **Cross-reactivity:** While the risk of cross-reactivity between sulfonamide antibiotics and non-antibiotics is debated, for exam purposes, they are considered contraindicated. * **Dermatological Emergency:** Always monitor for rashes when starting Zonisamide, as it can cause life-threatening SJS.

Question 70: Which of the following is NOT a known side effect of dapsone?

A. Hemolytic anemia
B. Myopathy (Correct Answer)
C. Hepatitis
D. Infectious mononucleosis type syndrome

Explanation: **Explanation:** Dapsone (Diaminodiphenyl sulfone) is a cornerstone in the treatment of leprosy and *Pneumocystis jirovecii* pneumonia. **Myopathy** is not a side effect of dapsone; it is more commonly associated with drugs like statins, colchicine, or zidovudine (AZT). **Analysis of Options:** * **Hemolytic Anemia (Option A):** This is the most common dose-related side effect. Dapsone causes oxidative stress on red blood cells. It is particularly severe in patients with **G6PD deficiency**, making G6PD screening essential before starting therapy. * **Hepatitis (Option C):** Dapsone can cause drug-induced liver injury, ranging from mild transaminitis to severe cholestatic jaundice as part of a hypersensitivity reaction. * **Infectious Mononucleosis-type Syndrome (Option D):** Also known as **"Dapsone Syndrome,"** this is a severe hypersensitivity reaction occurring 4–6 weeks after starting therapy. It is characterized by a triad of fever, malaise, and lymphadenopathy, often accompanied by jaundice and exfoliative dermatitis. It mimics infectious mononucleosis but is drug-induced. **High-Yield Clinical Pearls for NEET-PG:** * **Methemoglobinemia:** Dapsone frequently causes methemoglobinemia (presents as "chocolate-colored blood" and cyanosis). * **Lepra Reactions:** Dapsone is used in MDT for leprosy but does not prevent Type 1 or Type 2 lepra reactions. * **Mechanism:** It inhibits dihydropteroate synthase (folate synthesis inhibitor), similar to sulfonamides. * **Agranulocytosis:** A rare but life-threatening idiosyncratic reaction.

Practice by Chapter

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Aminoglycosides

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Sulfonamides and Trimethoprim

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Antimycobacterial Drugs

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Antifungal Agents

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Antiparasitic Agents

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Antimicrobial Resistance

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