Antimicrobial Agents Practice Questions

Q: Which of the following is a known side effect of zidovudine?

Granulocytopenia. Zidovudine (AZT) is a Nucleoside Reverse Transcriptase Inhibitor (NRTI) used in the management of HIV/AIDS. The correct answer is Granulocytopenia because the most significant and dose-limiting toxicity of zidovudine is bone marrow suppression. 1. Why Granulocytopenia is correct: Zidovudine inhibits DNA polymerase-gamma in host cells, leading to mitochondrial toxicity and interference with rapidly dividing cells [1], [2]. This results in significant myelosuppression, manifesting primarily as anemia (macrocytic) and granulocytopenia/neutropenia. This effect is additive when used with other myelosuppressive drugs like ganciclovir or trimethoprim-sulfamethoxazole. 2. Why other options are incorrect: * Headache and Myalgia (Options A & B): While these can occur as non-specific constitutional symptoms during the initiation of therapy, they are not the "signature" or dose-limiting toxicities tested in competitive exams. (Note: Zidovudine causes a specific myopathy, but granulocytopenia is the more classic hematological side effect). * Rashes (Option D): Rashes are more characteristic of Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs) like Nevirapine (which can cause Stevens-Johnson Syndrome) or the NRTI Abacavir (hypersensitivity reaction). High-Yield Clinical Pearls for NEET-PG: * Mnemonic: Zidovudine causes "Zapped" Bone Marrow (Anemia and Neutropenia). * Drug of Choice: Zidovudine is the preferred drug for preventing vertical transmission (mother-to-child) of HIV during pregnancy and labor. * Lactic Acidosis: Like all NRTIs, it carries a risk of lactic acidosis and hepatic steatosis [2]. * Monitoring: Patients on AZT require regular monitoring of Hemoglobin and Absolute Neutrophil Count (ANC).

Q: Ethambutol is safer in a patient with which of the following conditions?

Liver disease. **Explanation:** The correct answer is **Liver disease** because Ethambutol is primarily excreted unchanged by the kidneys (approx. 80%) and undergoes minimal hepatic metabolism. Unlike other first-line anti-tubercular drugs (HRZ—Isoniazid, Rifampicin, and Pyrazinamide), Ethambutol is **not hepatotoxic**. Therefore, it is the drug of choice or a safer alternative when treating tuberculosis in patients with pre-existing chronic liver disease. **Analysis of Incorrect Options:** * **Kidney disease:** Since Ethambutol is mainly excreted via the renal route, it accumulates in renal failure, increasing the risk of dose-dependent toxicity (optic neuritis). Dosage adjustment or avoidance is necessary in renal impairment. * **Gout:** Ethambutol interferes with the renal excretion of uric acid, leading to **hyperuricemia**. This can precipitate an acute attack of gout, making it unsafe for these patients. * **Both liver and kidney disease:** While safe for the liver, its significant risk in renal failure makes this option incorrect. **High-Yield NEET-PG Pearls:** * **Mechanism of Action:** Inhibits **Arabinosyl transferase**, thereby blocking the synthesis of Arabinogalactan in the mycobacterial cell wall. * **Key Side Effect:** **Retrobulbar Optic Neuritis**, manifesting as decreased visual acuity and **Red-Green color blindness**. It is generally reversible upon discontinuation. * **Monitoring:** Monthly visual acuity and color vision testing are mandatory for patients on Ethambutol. * **Pediatric Note:** It is often avoided in young children (usually <6 years) because they cannot reliably report changes in visual acuity or color perception.

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.

Question 1

Why does artemisinin-based combination therapy (ACT) reduce transmission of malaria more effectively than monotherapy?

Accepted Answer

It achieves faster parasite clearance reducing gametocyte production

Answer

It directly inhibits mosquito midgut development

Answer

It prevents sequestration of parasites

Answer

It kills gametocytes more rapidly

Question 2

Which of the following is a known side effect of zidovudine?

Accepted Answer

Granulocytopenia

Answer

Headache

Answer

Myalgia

Answer

Rashes

Question 3

Which of the following drug combinations demonstrates antimicrobial synergism?

Accepted Answer

Penicillin plus Streptomycin in subacute bacterial endocarditis

Answer

Ampicillin plus Tetracycline in endocarditis

Answer

Sulfamethoxazole plus Trimethoprim in urinary tract infections

Answer

Amphotericin B plus Flucytosine in cryptococcal meningitis

Question 4

Ethambutol is safer in a patient with which of the following conditions?

Accepted Answer

Liver disease

Answer

Kidney disease

Answer

Gout

Answer

Both liver and kidney disease

Question 5

Which of the following is a neuraminidase inhibitor?

Accepted Answer

Oseltamivir

Answer

Amantadine

Answer

Enfuviide

Answer

Formivirsen

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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