Antimicrobial Agents Practice Questions

Q: Which of the following is a neuraminidase inhibitor?

Oseltamivir. **Explanation:** **Correct Answer: A. Oseltamivir** Oseltamivir is a **Neuraminidase Inhibitor** used for the treatment and prophylaxis of Influenza A and B. Neuraminidase is a viral enzyme responsible for cleaving sialic acid residues on the host cell surface. By inhibiting this enzyme, Oseltamivir prevents the release of newly formed virions from infected cells, thereby limiting the spread of infection within the respiratory tract. It is administered orally as a prodrug. **Analysis of Incorrect Options:** * **B. Amantadine:** This is an **M2 ion channel blocker**. It prevents the "uncoating" of the Influenza A virus. It is ineffective against Influenza B and is currently rarely used due to widespread resistance. * **C. Enfuvirtide:** This is a **Fusion Inhibitor** used in HIV/AIDS. It binds to the gp41 subunit of the viral envelope glycoprotein, preventing the virus from fusing with the host CD4 cell membrane. * **D. Fomivirsen:** This is an **Antisense Oligonucleotide**. It was used (now discontinued) for the intravitreal treatment of CMV retinitis. It works by binding to viral mRNA to inhibit protein synthesis. **High-Yield NEET-PG Pearls:** * **Zanamivir** is another neuraminidase inhibitor but is administered via **inhalation** (contraindicated in asthma/COPD due to bronchospasm). * **Peramivir** is the IV neuraminidase inhibitor used for emergency/severe cases. * **Baloxavir Marboxil** is a newer drug for Influenza that inhibits **Cap-dependent Endonuclease**, blocking viral RNA synthesis. * Oseltamivir must be started within **48 hours** of symptom onset for maximum clinical benefit.

Q: The oropharyngeal and oesophageal candidiasis following long-term therapy with a broad-spectrum antibiotic can be best treated with?

Fluconazole. **Explanation:** The clinical scenario describes **Opportunistic Candidiasis** (Oropharyngeal and Oesophageal) resulting from the suppression of normal protective bacterial flora by broad-spectrum antibiotics. **Why Fluconazole is the Correct Answer:** Fluconazole is the **drug of choice** for both oropharyngeal and oesophageal candidiasis. It is a triazole antifungal that inhibits the enzyme *14-alpha-demethylase*, preventing the synthesis of ergosterol. It is preferred because of its **excellent oral bioavailability**, high efficacy, and superior safety profile compared to older antifungals. For oesophageal involvement (which is considered a systemic/deep infection), systemic therapy with Fluconazole is mandatory. **Analysis of Incorrect Options:** * **A. Griseofulvin:** This is an antifungal used exclusively for **Dermatophytosis** (skin, hair, and nail infections). It is completely ineffective against *Candida* species. * **B. Amphotericin B:** While highly effective against *Candida*, it is reserved for **severe, refractory, or life-threatening systemic fungal infections** due to its significant nephrotoxicity and requirement for intravenous administration. It is not the first-line treatment for uncomplicated mucosal candidiasis. * **D. Sulfonates:** These are not standard antifungal agents used for treating mucosal candidiasis. **NEET-PG High-Yield Pearls:** * **Drug of Choice (DOC):** For Oropharyngeal Candidiasis (Thrush) in HIV/Immunocompromised patients is **Fluconazole**. * **Vaginal Candidiasis:** A single 150 mg oral dose of Fluconazole is the standard treatment. * **Resistance:** *Candida krusei* and *Candida glabrata* often show inherent or acquired resistance to Fluconazole; in such cases, Echinocandins (e.g., Caspofungin) or Voriconazole are used. * **Side Effect:** Fluconazole is a known inhibitor of CYP450 enzymes, leading to potential drug interactions (e.g., increasing Warfarin or Phenytoin levels).

Q: Testing of HLA-B' 5701 is recommended prior to initiation of which antiretroviral agent?

Abacavir. The correct answer is **Abacavir (Option D)**. **1. Why Abacavir is Correct:** Abacavir is a Nucleoside Reverse Transcriptase Inhibitor (NRTI) associated with a severe, potentially life-threatening **Hypersensitivity Reaction (HSR)** [1]. This reaction is strongly linked to the presence of the **HLA-B*57:01** allele. In individuals carrying this allele, abacavir binds to the HLA-B*57:01 protein, altering the shape of the antigen-binding cleft [1]. This causes the immune system to recognize self-peptides as foreign, triggering a massive T-cell response. Screening for this allele is now a standard of care; if a patient tests positive, abacavir is strictly contraindicated [1]. **2. Why Other Options are Incorrect:** * **Atazanavir (A):** A Protease Inhibitor (PI) known for causing unconjugated hyperbilirubinemia (jaundice) by inhibiting the UGT1A1 enzyme, but it is not linked to HLA-B*57:01 [1]. * **Nelfinavir (B):** An older PI primarily associated with gastrointestinal side effects (diarrhea). No specific HLA screening is required. * **Raltegravir (C):** An Integrase Strand Transfer Inhibitor (INSTI). While it can rarely cause Stevens-Johnson Syndrome (SJS), there is no routine pharmacogenetic screening recommended prior to its use. **3. High-Yield Clinical Pearls for NEET-PG:** * **Abacavir HSR Symptoms:** Fever, rash, GI distress, and respiratory symptoms. **Re-challenge** after a suspected reaction is **fatal**. * **Other High-Yield HLA Associations:** * **HLA-B*15:02:** Carbamazepine-induced SJS/TEN (specifically in Asian populations). * **HLA-B*58:01:** Allopurinol-induced severe cutaneous adverse reactions (SCAR). * **Mnemonic:** "A-B-C" — **A**bacavir **B**inds **C**left of HLA-B*57:01.

Q: What are the drugs of choice for the treatment of neurocysticercosis?

Albendazole and praziquantel. **Explanation:** Neurocysticercosis (NCC), caused by the larval stage of the pork tapeworm *Taenia solium*, is a leading cause of adult-onset seizures in developing countries. The management depends on the stage and number of cysts. **Why Albendazole and Praziquantel are correct:** * **Albendazole:** It is the primary anthelmintic of choice due to its superior penetration into the cerebrospinal fluid (CSF) and brain parenchyma. It inhibits microtubule synthesis in the parasite. * **Praziquantel:** It increases the permeability of the parasite cell membrane to calcium, causing paralysis. * **Combination Therapy:** For patients with multiple viable parenchymal cysts (>2 cysts), the combination of Albendazole and Praziquantel is more effective than monotherapy in achieving complete cyst resolution. * *Note:* Corticosteroids (e.g., Dexamethasone) are always co-administered to reduce the inflammatory response triggered by dying parasites. **Why other options are incorrect:** * **Option A & B:** **Metronidazole** is an antiprotozoal/antibiotic used for anaerobic infections and amoebiasis. **Hydroquinone** is a skin-bleaching agent. **Pyrantel pamoate** is used for luminal helminthes (like pinworms) and has poor systemic absorption. * **Option D:** **Cyclophosphamide** is an alkylating cytotoxic chemotherapy agent/immunosuppressant, irrelevant to parasitic infections. **High-Yield Clinical Pearls for NEET-PG:** 1. **Drug of Choice (Single Cyst):** Albendazole monotherapy. 2. **Drug of Choice (Multiple Cysts):** Albendazole + Praziquantel. 3. **Calcified Cysts:** Anthelmintics are NOT required; management is symptomatic (Antiepileptics). 4. **Ocular/Spinal Cysticercosis:** Anthelmintics are generally avoided initially as inflammation can cause irreversible damage (blindness/cord compression). 5. **Pre-treatment:** Always rule out ocular cysticercosis via fundoscopy before starting anthelmintics.

Q: Which drug commonly causes impaired taste?

Metronidazole. **Explanation:** **Metronidazole** is a nitroimidazole antibiotic widely used for anaerobic bacterial and protozoal infections [1]. A classic, high-yield side effect of Metronidazole is a **metallic taste (dysgeusia)**. This occurs because the drug and its metabolites are secreted into the saliva, interacting directly with taste receptors. Patients should also be warned about the **disulfiram-like reaction** when consuming alcohol with this medication. **Analysis of Incorrect Options:** * **Losartan:** As an Angiotensin II Receptor Blocker (ARB), it is less likely to cause taste disturbances compared to ACE inhibitors (like Captopril), which are notorious for causing dysgeusia due to zinc chelation. * **Paracetamol (Acetaminophen):** Its primary toxicity is hepatotoxicity (centrilobular necrosis) mediated by the metabolite NAPQI. It does not typically affect taste. * **Aspirin:** The hallmark toxicity of aspirin (salicylism) includes tinnitus, vertigo, and respiratory alkalosis [2], but not impaired taste. **NEET-PG High-Yield Pearls:** * **Drugs causing Metallic Taste:** Metronidazole, Tinidazole, Clarithromycin, Lithium, Captopril, Carbonic anhydrase inhibitors (Acetazolamide), and Disulfiram [1]. * **Metronidazole Mnemonic (Side Effects):** **M**etallic taste, **E**ncephalopathy (rare), **T**oxicity with alcohol (Disulfiram-like), **R**eddish-brown urine (harmless metabolite). * **Clinical Note:** Always counsel patients on Metronidazole to avoid alcohol for at least 48–72 hours after the last dose to prevent severe vomiting and flushing.

Q: Albendazole is effective against all of the following helminths except:

Tapeworm. **Explanation:** Albendazole is a broad-spectrum anthelmintic belonging to the **Benzimidazole** group. Its primary mechanism of action involves inhibiting **microtubule synthesis** by binding to β-tubulin, which leads to glucose depletion and the eventual death of the parasite. **Why Tapeworm is the correct answer (the exception):** While Albendazole has some activity against certain larval forms of cestodes (e.g., Neurocysticercosis caused by *T. solium* or Hydatid disease by *Echinococcus*), it is **not** the drug of choice for adult intestinal tapeworms. For adult tapeworm infestations, **Praziquantel** or **Niclosamide** are significantly more effective and are considered the standard treatments. **Why the other options are incorrect:** * **Roundworm (*Ascaris lumbricoides*):** Albendazole is highly effective and considered a first-line treatment for Ascariasis. * **Hookworm (*Ancylostoma duodenale/Necator americanus*):** Albendazole is the preferred agent for hookworm infections, often used in mass deworming programs. * **Pinworm (*Enterobius vermicularis*):** Albendazole is the drug of choice. A single dose repeated after two weeks is standard therapy to prevent reinfection. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Albendazole is the DOC for **Hydatid disease** (*E. granulosus*) and **Neurocysticercosis**. * **Absorption:** Its absorption is significantly **increased when taken with a fatty meal**, which is crucial when treating systemic infections (like Hydatid cysts). * **Contraindication:** It is generally avoided during **pregnancy** due to potential embryotoxic and teratogenic effects. * **Mebendazole vs. Albendazole:** Albendazole is preferred over Mebendazole for systemic infections because it is better absorbed from the GI tract.

Q: Which is a glycoprotein, produced by many mammalian cells, and used in the treatment of hepatitis, papillomaviruses, hairy-cell leukemia, and AIDS-related Kaposi's sarcoma?

Interferon. **Explanation:** **Correct Answer: A. Interferon** Interferons (IFNs) are endogenous **glycoproteins** produced by host cells in response to viral infections, tumors, and other biological inducers. They act by binding to specific cell surface receptors, triggering the synthesis of enzymes (like 2’,5’-oligoadenylate synthetase) that inhibit viral protein synthesis and degrade viral RNA. * **Clinical Utility:** Interferon-alpha (IFN-α) is the specific subtype used for the conditions mentioned. It has potent antiviral and antiproliferative properties, making it the drug of choice for **Hairy-cell leukemia**, **Kaposi’s sarcoma** (in AIDS patients), **Chronic Hepatitis B and C**, and **Condyloma acuminatum** (caused by Papillomaviruses). **Why other options are incorrect:** * **B. Idoxuridine:** A pyrimidine analogue used primarily as a topical antiviral for Herpes Simplex Keratitis. It is not a glycoprotein and is too toxic for systemic use. * **C. Zidovudine (AZT):** A nucleoside reverse transcriptase inhibitor (NRTI). While used in AIDS, it is a synthetic drug, not a glycoprotein, and is not used for Hairy-cell leukemia or Hepatitis. * **D. Zalcitabine:** Another NRTI used in HIV treatment. Like Zidovudine, it lacks the broad-spectrum anticancer and glycoprotein properties of Interferons. **NEET-PG High-Yield Pearls:** * **Interferon-alpha:** Used in Hairy-cell leukemia, Kaposi’s sarcoma, and Hepatitis B/C. * **Interferon-beta:** Used primarily in **Multiple Sclerosis** to reduce the frequency of relapses. * **Interferon-gamma:** Used in **Chronic Granulomatous Disease** to reduce infections. * **Side Effects:** The most common side effect is a **"Flu-like syndrome"** (fever, chills, myalgia) and dose-limiting bone marrow suppression.

Q: What is the drug of choice for amoebic liver abscess?

Metronidazole. **Explanation:** **Metronidazole** is the drug of choice (DOC) for **amoebic liver abscess (ALA)** and all forms of invasive amoebiasis [1]. It is a nitroimidazole that acts as a potent tissue amoebicide. It is rapidly absorbed from the GI tract and achieves high therapeutic concentrations in the liver, effectively killing the trophozoites of *Entamoeba histolytica*. **Analysis of Options:** * **Metronidazole (Correct):** It is the first-line treatment due to its high efficacy and safety profile [2]. Following a course of Metronidazole, a **luminal amoebicide** (e.g., Diloxanide furoate or Paromomycin) must be administered to eradicate any surviving cysts in the colon and prevent relapse [1]. * **Ciprofloxacin:** This is a fluoroquinolone antibiotic used for bacterial infections (like bacillary dysentery) but has no significant activity against *E. histolytica*. * **Emetine:** While a potent tissue amoebicide, it is now rarely used due to its high toxicity, particularly **cardiotoxicity** (arrhythmias and hypotension). It is reserved only for severe cases where nitroimidazoles are contraindicated. * **Chloroquine:** It reaches high concentrations in the liver and was historically used for ALA. However, it is less effective than Metronidazole and is now considered a second-line agent, usually used in combination with other drugs if Metronidazole fails. **High-Yield Clinical Pearls for NEET-PG:** * **DOC for Asymptomatic Cyst Passers:** Diloxanide furoate (Luminal amoebicide) [2]. * **Tinidazole/Secnidazole:** These are longer-acting congeners of Metronidazole often preferred for better compliance (shorter dosage schedule) [1]. * **Aspiration of ALA:** Not routinely required unless the abscess is large (>10 cm), at risk of rupture, or fails to respond to drug therapy within 72 hours. The aspirated pus typically resembles **"Anchovy sauce."**

Q: A 5-year-old female presents with fever, headache, and confusion. A provisional diagnosis of bacterial meningitis is made. The child had a severe allergic reaction to penicillin approximately six months prior. After admission, intravenous antibiotics were started. Investigations revealed: Hemoglobin – 6.0 g/L, Erythrocyte count – 1.2 x 10^6/mm^3, Platelets – 60,000/mm^3, Leukocyte count – 1500/mm^3. Which of the following is the most likely drug responsible for these findings?

Chloramphenicol. **Explanation:** The clinical presentation of fever, headache, and confusion suggests **bacterial meningitis**. The patient has a history of severe penicillin allergy, which limits the use of beta-lactams (like Ceftriaxone). Historically, **Chloramphenicol** was a primary alternative for meningitis in penicillin-allergic patients due to its excellent blood-brain barrier penetration. The laboratory findings (Hb: 6.0 g/L, WBC: 1500/mm³, Platelets: 60,000/mm³) indicate **pancytopenia**, suggesting bone marrow suppression. Chloramphenicol is notorious for causing two types of bone marrow toxicity: 1. **Dose-dependent anemia:** Reversible suppression of erythropoiesis. 2. **Idiosyncratic Aplastic Anemia:** A rare, unpredictable, and often fatal condition leading to pancytopenia (as seen in this case). **Analysis of Incorrect Options:** * **Gentamicin:** An aminoglycoside primarily associated with **nephrotoxicity** and **ototoxicity**. It does not cause pancytopenia and has poor CNS penetration. * **Doxycycline:** A tetracycline generally contraindicated in children under 8 years (due to tooth discoloration). Its primary side effects are GI upset and photosensitivity, not bone marrow failure. * **Vancomycin:** Used for MRSA or penicillin-resistant pneumococci. Its classic side effects include **Red Man Syndrome** and nephrotoxicity, but it does not typically cause aplastic anemia. **NEET-PG High-Yield Pearls:** * **Chloramphenicol Toxicity:** Remember the mnemonic **"Gray Baby Syndrome"** (due to deficient glucuronidation in neonates) and **Aplastic Anemia**. * **Mechanism of Action:** Inhibits protein synthesis by binding to the **50S ribosomal subunit**. * **Drug of Choice:** Though largely replaced by Cephalosporins, it remains a backup for Rickettsial infections and Typhoid fever in specific settings.

Q: Which of the following fluoroquinolones has the broadest spectrum of activity against bacteria?

Trovafloxacin. **Explanation:** The correct answer is **Trovafloxacin**. Fluoroquinolones are classified into generations based on their spectrum of activity. Trovafloxacin belongs to the **fourth generation**, which represents the broadest spectrum in this class. **Why Trovafloxacin is correct:** Fourth-generation fluoroquinolones (like Trovafloxacin and Moxifloxacin) retain the Gram-negative coverage of earlier generations but significantly enhance activity against **Gram-positive cocci** (especially *S. pneumoniae*) and **anaerobes** (like *Bacteroides fragilis*). Trovafloxacin was the first to offer reliable anaerobic coverage, making it the broadest agent among the options. **Why the other options are incorrect:** * **Nalidixic acid:** A first-generation quinolone with a very narrow spectrum, limited only to Gram-negative bacteria causing uncomplicated UTIs. It lacks systemic activity. * **Norfloxacin:** A second-generation fluoroquinolone. While it has improved Gram-negative coverage compared to Nalidixic acid, it has poor systemic distribution and minimal Gram-positive activity. * **Ciprofloxacin:** Also a second-generation agent. It is highly potent against Gram-negative bacteria (including *Pseudomonas*) but has relatively weak activity against Gram-positive organisms and lacks anaerobic coverage. **High-Yield Clinical Pearls for NEET-PG:** * **The "Respiratory Quinolones":** Levofloxacin, Moxifloxacin, and Gemifloxacin are called this due to their excellent activity against *Streptococcus pneumoniae*. * **Pseudomonas coverage:** Ciprofloxacin is the most potent fluoroquinolone against *Pseudomonas aeruginosa*. * **Safety Note:** Trovafloxacin is rarely used clinically today due to the risk of **severe hepatotoxicity**, but it remains a classic exam answer for the "broadest spectrum" question. * **Mechanism of Action:** They inhibit **DNA Gyrase** (Gram-negative) and **Topoisomerase IV** (Gram-positive).

Question 1

Which of the following is a neuraminidase inhibitor?

Accepted Answer

Oseltamivir

Answer

Amantadine

Answer

Enfuviide

Answer

Formivirsen

Question 2

The oropharyngeal and oesophageal candidiasis following long-term therapy with a broad-spectrum antibiotic can be best treated with?

Accepted Answer

Fluconazole

Answer

Griseofulvin

Answer

Amphotericin

Answer

Sulfonates

Question 3

Testing of HLA-B' 5701 is recommended prior to initiation of which antiretroviral agent?

Accepted Answer

Abacavir

Answer

Atazanavir

Answer

Nelfinavir

Answer

Raltegravir

Question 4

What are the drugs of choice for the treatment of neurocysticercosis?

Accepted Answer

Albendazole and praziquantel

Answer

Hydroquinone and metronidazole

Answer

Metronidazole and pyrantel pamoate

Answer

Cyclophosphamide

Question 5

Which drug commonly causes impaired taste?

Accepted Answer

Metronidazole

Answer

Losartan

Answer

Paracetamol

Answer

Aspirin

Question 6

Albendazole is effective against all of the following helminths except:

Accepted Answer

Tapeworm

Answer

Roundworm

Answer

Hookworm

Answer

Pinworm

Question 7

Which is a glycoprotein, produced by many mammalian cells, and used in the treatment of hepatitis, papillomaviruses, hairy-cell leukemia, and AIDS-related Kaposi's sarcoma?

Accepted Answer

Interferon

Answer

Idoxuridine

Answer

Zidovudine

Answer

Zalcitabine

Question 8

What is the drug of choice for amoebic liver abscess?

Accepted Answer

Metronidazole

Answer

Ciprofloxacin

Answer

Emetine

Answer

Chloroquine

Question 9

A 5-year-old female presents with fever, headache, and confusion. A provisional diagnosis of bacterial meningitis is made. The child had a severe allergic reaction to penicillin approximately six months prior. After admission, intravenous antibiotics were started. Investigations revealed: Hemoglobin – 6.0 g/L, Erythrocyte count – 1.2 x 10^6/mm^3, Platelets – 60,000/mm^3, Leukocyte count – 1500/mm^3. Which of the following is the most likely drug responsible for these findings?

Accepted Answer

Chloramphenicol

Answer

Gentamicin

Answer

Doxycycline

Answer

Vancomycin

Question 10

Which of the following fluoroquinolones has the broadest spectrum of activity against bacteria?

Accepted Answer

Trovafloxacin

Answer

Ciprofloxacin

Answer

Norfloxacin

Answer

Nalidixic acid

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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