Antimicrobial Agents Practice Questions

Q: What is the recommended drug for chemoprophylaxis of plague?

Tetracycline. **Explanation:** Plague, caused by the Gram-negative coccobacillus *Yersinia pestis*, is a severe zoonotic infection. For **chemoprophylaxis**, the goal is to prevent the onset of disease in individuals exposed to infected fleas or patients with pneumonic plague. **Why Tetracycline is correct:** Tetracyclines (specifically **Tetracycline** or **Doxycycline**) are the drugs of choice for chemoprophylaxis. They are orally bioavailable, cost-effective, and highly active against *Y. pestis*. Doxycycline is often preferred in clinical practice due to its twice-daily dosing schedule. Sulfonamides (like Cotrimoxazole) are considered second-line alternatives. **Why the other options are incorrect:** * **Streptomycin:** While it is the **drug of choice for the treatment** of established bubonic or pneumonic plague, it is administered parenterally (IM) and carries risks of ototoxicity and nephrotoxicity, making it unsuitable for prophylaxis. * **Erythromycin:** This macrolide has poor activity against *Yersinia pestis* and is not used in the management of plague. * **Vancomycin:** This glycopeptide is exclusively active against Gram-positive bacteria (e.g., MRSA). It has no role in treating Gram-negative infections like plague. **High-Yield Clinical Pearls for NEET-PG:** * **Treatment of Choice:** Streptomycin (Gentamicin is a preferred alternative due to better availability and lower toxicity). * **Prophylaxis of Choice:** Doxycycline or Tetracycline. * **Vector:** Oriental rat flea (*Xenopsylla cheopis*). * **Safety Note:** Avoid tetracyclines in children under 8 years and pregnant women (due to bone growth retardation and tooth discoloration); use Sulfonamides or Ciprofloxacin instead.

Q: A 16-year-old female patient presents with complaints of a non-productive cough, low grade fever, and a headache. The physician also notes a non-purulent otitis media. She is treated with an antibiotic that inhibits the translocation of the growing peptide chain along the mRNA. Which antibiotic was given?

Erythromycin. ### Explanation **1. Why Erythromycin is Correct:** The clinical presentation (non-productive cough, low-grade fever, and headache in a teenager) is classic for **Atypical Pneumonia**, most commonly caused by *Mycoplasma pneumoniae*. The presence of **bullous myringitis** (non-purulent otitis media) is a high-yield diagnostic clue for *Mycoplasma*. The drug of choice for *Mycoplasma* is a **Macrolide** (e.g., Erythromycin, Azithromycin). * **Mechanism of Action:** Macrolides bind to the **50S ribosomal subunit** and inhibit protein synthesis by blocking the **translocation** step (the movement of the growing peptide chain from the A-site to the P-site along the mRNA). **2. Why Other Options are Incorrect:** * **Chloramphenicol (A):** While it binds to the 50S subunit, its primary mechanism is inhibiting **peptidyl transferase**, not translocation. It is also not the first-line treatment for atypical pneumonia due to toxicity (e.g., Bone marrow suppression, Gray Baby Syndrome). * **Cycloheximide (B):** This inhibits protein synthesis in **eukaryotes** only. It is used in laboratory research and is not a clinical antibiotic. * **Puromycin (C):** It acts as an analog of aminoacyl-tRNA and causes **premature chain termination** in both prokaryotes and eukaryotes. It is not used clinically due to its lack of selectivity. **3. NEET-PG High-Yield Pearls:** * **Mnemonic for 50S Inhibitors:** **"CCEL"** (Chloramphenicol, Clindamycin, Erythromycin/Macrolides, Linezolid). * **Translocation Inhibitors:** Macrolides and Clindamycin. * **Mycoplasma pneumoniae:** Lacks a cell wall (intrinsically resistant to Beta-lactams); diagnosed via Cold Agglutinin test. * **Erythromycin Side Effects:** Motilin receptor stimulation (diarrhea), Cholestatic jaundice, and QT prolongation.

Q: A permanent staining of teeth in infants may be produced due to the administration of which of the following medications during pregnancy?

Tetracyclines. **Tetracyclines** are the correct answer because they are known for their high affinity for calcium. They form a stable **calcium-orthophosphate complex** that is deposited in bones and teeth during the process of mineralization [2]. When administered during pregnancy (specifically from the second trimester onwards), tetracyclines cross the placenta and deposit in the developing deciduous teeth of the fetus. This results in **permanent brownish-yellow discoloration** and possible enamel hypoplasia [1].**Analysis of Incorrect Options:** Chloramphenicol: Associated with **"Gray Baby Syndrome"** in neonates due to deficient glucuronidation and inadequate renal excretion, leading to cardiovascular collapse, but it does not affect teeth. Erythromycin: Generally considered safe in pregnancy (except for the estolate salt, which may cause cholestatic hepatitis in the mother). It does not cause dental staining. Amoxycillin: A penicillin-group drug that is safe during pregnancy and does not interfere with mineralized tissues.**High-Yield NEET-PG Pearls:** Timing: Tetracyclines affect deciduous teeth if given after the 14th week of gestation and permanent teeth if given to children between birth and 8 years of age. Contraindications: Tetracyclines are **Category D** drugs in pregnancy and are contraindicated in children under 8 years. Fanconi Syndrome: Use of **outdated/expired tetracyclines** can lead to proximal renal tubular acidosis (Fanconi Syndrome). Doxycycline: Among tetracyclines, doxycycline is least likely to cause significant calcium binding, but it is still clinically avoided in these populations.

Q: What is the dose-limiting toxicity of amphotericin B?

Renal tubular acidosis. **Explanation:** Amphotericin B is a potent polyene antifungal that acts by binding to ergosterol in fungal cell membranes, creating pores [1]. However, it also binds to cholesterol in human membranes, leading to significant toxicity. **Why Renal Tubular Acidosis (RTA) is the correct answer:** Nephrotoxicity is the most significant and **dose-limiting toxicity** of Amphotericin B [1][2]. It occurs in nearly 80% of patients. The drug causes direct damage to the renal tubular epithelium, leading to increased permeability. This results in **Type 1 (Distal) Renal Tubular Acidosis**, characterized by the inability to excrete hydrogen ions. This is often accompanied by significant wasting of potassium (hypokalemia) and magnesium (hypomagnesemia). **Analysis of Incorrect Options:** * **A. Infusion-related reactions:** These are very common (fever, chills, rigors, "shake and bake" phenomenon) but are managed with premedication (NSAIDs, hydrocortisone) and are not typically dose-limiting [1]. * **C. Myelosuppression:** While anemia (due to decreased erythropoietin production by damaged kidneys) can occur, it is not the primary dose-limiting factor. * **D. Hypotension:** This can occur during rapid infusion but is a transient hemodynamic effect rather than a cumulative dose-limiting toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Liposomal Amphotericin B:** Developed to reduce nephrotoxicity by targeting the drug specifically to fungal cells and sparing renal tubules [1][2]. * **Pre-loading:** To minimize nephrotoxicity, "salt loading" (infusion of 1 liter of normal saline) is recommended before administration. * **Monitoring:** Always monitor serum creatinine, potassium, and magnesium levels during therapy. * **Drug of Choice:** Despite toxicity, it remains the gold standard for most systemic fungal infections (e.g., Mucormycosis, Cryptococcal meningitis).

Q: Which of the following drugs can be used in the treatment of both Human Immunodeficiency Virus (HIV) and Hepatitis B virus (HBV) infection?

Emtricitabine. **Explanation:** The correct answer is **Emtricitabine**. **Why it is correct:** Emtricitabine (FTC) is a Nucleoside Reverse Transcriptase Inhibitor (NRTI). It acts by inhibiting the enzyme **Reverse Transcriptase** in HIV and **DNA Polymerase** in Hepatitis B Virus (HBV). Because both viruses utilize a reverse transcription step in their replication cycles, certain NRTIs are effective against both. Emtricitabine is a fluorinated analog of Lamivudine and is frequently used in "backbone" antiretroviral therapy (ART) for patients co-infected with HIV and HBV. **Analysis of Incorrect Options:** * **Enfuvirtide (A):** This is a **fusion inhibitor** that binds to the gp41 subunit of the HIV viral envelope. It is specific to HIV-1 and has no activity against HBV. * **Abacavir (C):** While Abacavir is an NRTI used in HIV treatment, it is unique among its class because it **does not** have clinically significant activity against HBV. * **Acyclovir (D):** This is a guanosine analog used primarily for **Herpes Simplex Virus (HSV)** and Varicella-Zoster Virus (VZV). It is phosphorylated by viral thymidine kinase, an enzyme not utilized by HIV or HBV. **High-Yield Clinical Pearls for NEET-PG:** * **Dual-Action Drugs:** The three main drugs effective against both HIV and HBV are **Lamivudine (3TC), Emtricitabine (FTC), and Tenofovir (TDF/TAF).** * **Mnemonic:** "LET" them treat both (**L**amivudine, **E**mtricitabine, **T**enofovir). * **Clinical Caution:** If a patient co-infected with HIV/HBV is treated with these drugs and then stops, they may experience a severe **"flare-up" of Hepatitis B**. * **Abacavir Fact:** Always screen for the **HLA-B*5701** allele before starting Abacavir to avoid life-threatening hypersensitivity reactions.

Q: What is the commonest side effect of Dapsone?

Hemolytic anemia. **Explanation:** **Dapsone (Diaminodiphenyl sulfone)** is the cornerstone of multidrug therapy (MDT) for Leprosy. The most common side effect associated with Dapsone is **Hemolytic anemia**. **Why Hemolytic Anemia is the Correct Answer:** Dapsone is an oxidizing agent. Once ingested, it undergoes metabolism to form hydroxylamine derivatives which induce oxidative stress in red blood cells (RBCs). This leads to the oxidation of hemoglobin, resulting in the formation of Heinz bodies and subsequent hemolysis. While this can occur in any patient, it is significantly more severe and dose-dependent in individuals with **G6PD deficiency**, as they lack the necessary antioxidant protection (NADPH) to counteract oxidative damage. **Analysis of Incorrect Options:** * **Thrombocytopenia:** While Dapsone can rarely cause blood dyscrasias, it is not a common or characteristic side effect compared to its effects on RBCs. * **Cyanosis:** This is a known side effect caused by **Methemoglobinemia** (another oxidative effect of Dapsone). While clinically important, it is less frequent than the drop in hemoglobin levels seen in most patients. * **Bone marrow depression:** This is a rare, idiosyncratic reaction (part of the "Dapsone Syndrome") rather than the most common side effect. **High-Yield Clinical Pearls for NEET-PG:** * **Dapsone Syndrome:** A severe hypersensitivity reaction occurring 4–6 weeks after starting therapy, characterized by fever, exfoliative dermatitis, lymphadenopathy, and hepatitis. * **Methemoglobinemia:** Dapsone is a classic cause; patients may present with "chocolate-colored blood" and cyanosis unresponsive to oxygen. * **Drug of Choice:** Dapsone is also used for *Pneumocystis jirovecii* prophylaxis and is the gold standard for **Dermatitis Herpetiformis**. * **Pre-test:** Always screen for G6PD levels before initiating long-term Dapsone therapy.

Q: A client with acquired immunodeficiency syndrome is prescribed with Zidovudine (Azidothymidine). Which of the following laboratory results should the nurse monitor while on this medication?

Complete blood count.. **Explanation:** **Zidovudine (AZT)** is a Nucleoside Reverse Transcriptase Inhibitor (NRTI) used in the management of HIV/AIDS. The correct answer is **Complete Blood Count (CBC)** because the most significant and dose-limiting adverse effect of Zidovudine is **bone marrow suppression**. 1. **Why CBC is correct:** Zidovudine inhibits DNA polymerase-gamma in mitochondria and interferes with host cell DNA synthesis in the bone marrow. This leads to **macrocytic anemia** and **neutropenia**. Monitoring the CBC is vital to detect early signs of hematological toxicity, which may necessitate dose adjustment, drug holiday, or the administration of Erythropoietin/G-CSF. 2. **Why other options are incorrect:** * **Throat swab:** This is used to diagnose infections (like candidiasis or strep throat) but is not a monitoring parameter for Zidovudine toxicity. * **Random blood sugar:** While some Protease Inhibitors (PIs) cause hyperglycemia/diabetes, NRTIs like Zidovudine are not typically associated with acute glucose fluctuations. * **Blood uric acid:** Hyperuricemia is a side effect of drugs like Pyrazinamide or Ethambutol, not Zidovudine. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for AZT side effects:** **A**nemia, **Z**idovudine, **T**hrombocytopenia/Neutropenia. * **MCV Change:** An increase in Mean Corpuscular Volume (MCV) is often the first sign of Zidovudine therapy and can be used as a marker of patient compliance. * **Drug Interactions:** Avoid co-administration with **Stavudine (d4T)** as they compete for the same phosphorylation pathway (antagonism), and **Ganciclovir**, which exacerbates bone marrow toxicity. * **Pregnancy:** Zidovudine is a preferred agent for preventing vertical transmission (mother-to-child) of HIV.

Q: Which of the following antihelminthics acts by producing flaccid paralysis of the worm?

Piperazine. **Explanation:** The correct answer is **Piperazine**. Its mechanism of action is central to its clinical utility in treating *Ascaris lumbricoides* (roundworm) and *Enterobius vermicularis* (pinworm). **1. Why Piperazine is correct:** Piperazine acts as a **GABA (Gamma-Aminobutyric Acid) agonist** at the neuromuscular junction of the parasite. It causes hyperpolarization of the muscle membrane, leading to **flaccid paralysis**. Once paralyzed, the worms lose their grip on the intestinal wall and are expelled alive by normal peristalsis. This is distinct from agents that cause spastic paralysis (like Pyrantel pamoate). **2. Why the other options are incorrect:** * **Quinacrine:** An older antiprotozoal/anthelmintic that primarily interferes with DNA transcription and was used for Giardiasis and Cestodes; it does not cause flaccid paralysis. * **Diethylcarbamazine (DEC):** Used for Filariasis. It works by altering the organelle membranes of microfilariae and increasing their susceptibility to the host's immune system (phagocytosis). * **Mebendazole:** A benzimidazole that acts by **inhibiting microtubule synthesis** (binding to β-tubulin). This leads to glucose depletion and metabolic failure of the parasite, not immediate paralysis. **3. NEET-PG High-Yield Pearls:** * **Piperazine vs. Pyrantel Pamoate:** These two are physiological antagonists. While Piperazine causes *flaccid* paralysis (GABA agonist), Pyrantel pamoate causes *spastic* paralysis (Nicotinic agonist/AChE inhibitor). They should never be administered together. * **Clinical Caution:** Piperazine is generally avoided in patients with epilepsy or renal impairment as it can cause neurotoxicity (the "Snail and Dog" syndrome—ataxia and tremors). * **Drug of Choice (DOC):** For most intestinal nematodes, Albendazole/Mebendazole have replaced Piperazine due to broader coverage and simpler dosing.

Question 1

What is the recommended drug for chemoprophylaxis of plague?

Accepted Answer

Tetracycline

Answer

Streptomycin

Answer

Erythromycin

Answer

Vancomycin

Question 2

A 16-year-old female patient presents with complaints of a non-productive cough, low grade fever, and a headache. The physician also notes a non-purulent otitis media. She is treated with an antibiotic that inhibits the translocation of the growing peptide chain along the mRNA. Which antibiotic was given?

Accepted Answer

Erythromycin

Answer

Chloramphenicol

Answer

Cycloheximide

Answer

Puromycin

Question 3

A permanent staining of teeth in infants may be produced due to the administration of which of the following medications during pregnancy?

Accepted Answer

Tetracyclines

Answer

Chloramphenicol

Answer

Erythromycin

Answer

Amoxycillin

Question 4

What is the dose-limiting toxicity of amphotericin B?

Accepted Answer

Renal tubular acidosis

Answer

Infusion-related reactions

Answer

Myelosuppression

Answer

Hypotension

Question 5

Which of the following drugs can be used in the treatment of both Human Immunodeficiency Virus (HIV) and Hepatitis B virus (HBV) infection?

Accepted Answer

Emtricitabine

Answer

Enfuvirtide

Answer

Abacavir

Answer

Acyclovir

Question 6

What is the commonest side effect of Dapsone?

Accepted Answer

Hemolytic anemia

Answer

Thrombocytopenia

Answer

Cyanosis

Answer

Bone marrow depression

Question 7

A client with acquired immunodeficiency syndrome is prescribed with Zidovudine (Azidothymidine). Which of the following laboratory results should the nurse monitor while on this medication?

Accepted Answer

Complete blood count.

Answer

Throat swab gram stain.

Answer

Random blood sugar.

Answer

Blood uric acid.

Question 8

All the following drugs are active against Pseudomonas infections EXCEPT?

Accepted Answer

Azithromycin

Answer

Carbenicillin

Answer

Azlocillin

Answer

Piperacillin

Question 9

A patient with streptococcal endocarditis, susceptible to penicillin, develops an immediate allergic reaction after penicillin administration. Which drug can be used for management?

Accepted Answer

Vancomycin

Answer

Ceftriaxone

Answer

Meropenem

Answer

Carbenicillin

Question 10

Which of the following antihelminthics acts by producing flaccid paralysis of the worm?

Accepted Answer

Piperazine

Answer

Quinacrine

Answer

Diethylcarbamazine

Answer

Mebendazole

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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