Antimicrobial Agents Practice Questions

Q: Which antimalarial drug can be safely administered in a baby with glucose-6-phosphate dehydrogenase deficiency?

Mefloquine. **Explanation:** The core clinical concern in patients with **Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency** is the risk of **oxidative stress**. G6PD is essential for maintaining levels of NADPH, which keeps glutathione in its reduced state to neutralize free radicals. In its absence, oxidizing agents cause hemoglobin to precipitate (Heinz bodies), leading to acute hemolysis. **Why Mefloquine is the Correct Answer:** Mefloquine is a quinoline-methanol derivative that does not induce significant oxidative stress. It is considered safe for use in G6PD-deficient individuals for both prophylaxis and treatment of multidrug-resistant *P. falciparum*. **Analysis of Incorrect Options:** * **Primaquine (Option D):** This is the most notorious trigger for hemolysis in G6PD deficiency. It is an 8-aminoquinoline that generates reactive oxygen species. Testing for G6PD levels is mandatory before prescribing Primaquine for radical cure. * **Chloroquine (Option A) & Quinine (Option B):** While these drugs are generally considered "low risk" compared to Primaquine, they can still trigger hemolysis in individuals with severe G6PD variants (like the Mediterranean variant) or when administered in high doses. In the context of a "safest" choice among the options provided, Mefloquine carries the least oxidative risk. **NEET-PG High-Yield Pearls:** * **Radical Cure:** Primaquine is the only drug that kills hypnozoites (*P. vivax/ovale*), but it is strictly contraindicated in G6PD deficiency and pregnancy. * **Tafenoquine:** A newer long-acting 8-aminoquinoline that also requires G6PD testing before use. * **Safe Alternatives:** Besides Mefloquine, **Atovaquone-Proguanil** and **Artemisinins** are generally safe in G6PD-deficient patients. * **Drug of Choice:** Mefloquine is the preferred prophylactic agent for travelers going to areas with Chloroquine-resistant malaria, provided there are no neuropsychiatric contraindications.

Q: Which of the following statements regarding ivermectin is true?

All the above.. **Explanation:** Ivermectin is a broad-spectrum antiparasitic agent that acts by intensifying GABA-mediated neurotransmission and binding to glutamate-gated chloride channels, leading to the paralysis and death of the parasite. * **Option A (Strongyloidiasis):** Ivermectin is currently considered the **most effective drug** and the treatment of choice for *Strongyloides stercoralis* infection. It has a higher cure rate and better tolerability compared to older drugs like albendazole. * **Option B (Onchocerciasis):** It is the **drug of choice** for River Blindness (*Onchocerca volvulus*). It kills the microfilariae (microfilaricidal) but not the adult worms. A single dose can suppress microfilariae levels for up to a year. * **Option C (Scabies):** Oral ivermectin is highly effective for treating **scabies**, particularly in institutional outbreaks or for **Crusted (Norwegian) scabies**, where it is used in combination with topical permethrin. Since all individual statements are pharmacologically accurate, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Opens chloride channels in invertebrate nerve and muscle cells. * **Mazzotti Reaction:** Be aware of this reaction when treating onchocerciasis; it is an immune response to dying microfilariae (fever, rash, joint pain), though it is less severe with ivermectin than with diethylcarbamazine (DEC). * **Contraindication:** It should not be used in patients with a breached blood-brain barrier (e.g., meningitis) or in children weighing <15 kg. * **Other uses:** It is also used in Lymphatic Filariasis (in combination with Albendazole) and Pediculosis (head lice).

Q: Which of the following is NOT a true statement regarding vancomycin uses?

Drug of choice for pseudomembranous enterocolitis. **Explanation:** The correct answer is **B** because, according to current clinical guidelines (IDSA), **Oral Fidaxomicin** or **Oral Vancomycin** are both first-line treatments for *Clostridioides difficile* infection (pseudomembranous enterocolitis). However, the phrase "Drug of Choice" in medical exams often refers to the single most effective or preferred agent. While Vancomycin is a primary treatment, Fidaxomicin is increasingly preferred due to lower recurrence rates. More importantly, in the context of NEET-PG, this option is often considered "not true" because **Metronidazole** was historically the drug of choice for mild cases, and Vancomycin is only used **orally** (not IV) for this condition, as IV vancomycin does not reach the gut lumen. **Analysis of other options:** * **Option A:** Vancomycin is indicated for surgical prophylaxis (e.g., cardiac or orthopedic surgery) in hospitals with high MRSA prevalence or for patients allergic to penicillins/cephalosporins. * **Option C:** Vancomycin is highly effective and often used in combination with ceftriaxone for meningitis caused by highly penicillin-resistant *Streptococcus pneumoniae*. * **Option D:** Vancomycin remains a gold-standard treatment for serious infections caused by Methicillin-resistant *Staphylococcus aureus* (MRSA). **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Inhibits cell wall synthesis by binding to the **D-Ala-D-Ala** terminus of nascent peptidoglycan. * **Red Man Syndrome:** A common infusion-related reaction caused by histamine release; prevented by slowing the infusion rate. * **Resistance:** Occurs via a change in the binding site from D-Ala-D-Ala to **D-Ala-D-Lac**. * **Spectrum:** Exclusively Gram-positive coverage (too large to pass through Gram-negative porins).

Q: Which anti-HIV drug is known to cause myopathy that resembles mitochondrial myopathy with ragged red fibers?

Zidovudine. **Explanation:** **1. Why Zidovudine (AZT) is the correct answer:** Zidovudine is a Nucleoside Reverse Transcriptase Inhibitor (NRTI). While its primary target is the viral reverse transcriptase, it also inhibits **DNA polymerase-gamma**, the enzyme responsible for mitochondrial DNA replication. This leads to mitochondrial depletion and dysfunction. Clinically, this manifests as a toxic myopathy characterized by muscle weakness and elevated creatine kinase. Histologically, muscle biopsies show **"Ragged Red Fibers"** (due to compensatory mitochondrial proliferation) and cytochrome c oxidase deficiency, mimicking primary mitochondrial myopathies. **2. Why the other options are incorrect:** * **Enfuvirtide:** This is a fusion inhibitor that prevents HIV entry into cells. Its most common side effects are local injection site reactions; it does not cause mitochondrial toxicity. * **Nevirapine:** This is a Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI). It is primarily associated with hepatotoxicity and severe hypersensitivity reactions, such as Stevens-Johnson Syndrome (SJS). * **Tenofovir:** While an NRTI (specifically a nucleotide analog), Tenofovir is more commonly associated with **nephrotoxicity** (Fanconi syndrome) and a decrease in bone mineral density, rather than myopathy. **3. High-Yield Clinical Pearls for NEET-PG:** * **Zidovudine (AZT):** Most common side effect is **bone marrow suppression** (anemia and neutropenia). It is also used for the prevention of vertical transmission (mother-to-child). * **Lactic Acidosis:** This is a class-wide side effect of NRTIs due to mitochondrial toxicity (highest risk with Stavudine > Didanosine > Zidovudine). * **Mnemonic:** "Zidovudine makes the muscles and marrow **Z**apped."

Q: What is the drug of choice for Cryptosporidium parvum infection?

Nitazoxanide. **Explanation:** **Nitazoxanide** is the drug of choice for treating diarrhea caused by *Cryptosporidium parvum* in both children and immunocompetent adults. It is a prodrug that is converted to its active metabolite, **tizoxanide**, which interferes with the **pyruvate:ferredoxin oxidoreductase (PFOR) enzyme-dependent electron transfer reaction**. This reaction is essential for the anaerobic energy metabolism of the parasite. **Analysis of Options:** * **Nitazoxanide (Correct):** It is FDA-approved for cryptosporidiosis. While highly effective in immunocompetent patients, its efficacy is lower in HIV/AIDS patients, where highly active antiretroviral therapy (HAART) is the primary intervention to restore immune function. * **Cotrimoxazole:** This is the drug of choice for *Isospora belli*, *Cyclospora*, and *Pneumocystis jirovecii*, but it has no clinical activity against *Cryptosporidium*. * **Ivermectin:** This is a broad-spectrum anti-helminthic agent used primarily for *Strongyloides stercoralis*, Onchocerciasis, and Scabies. It is ineffective against protozoa like *Cryptosporidium*. * **Diiodohydroxyquinoline (Iodoquinol):** This is a luminal amebicide used for asymptomatic *Entamoeba histolytica* infections or as adjunct therapy in amebic liver abscess. It does not cover *Cryptosporidium*. **High-Yield Facts for NEET-PG:** * **Cryptosporidiosis** is a major cause of chronic, voluminous "cholera-like" diarrhea in **HIV/AIDS** patients (CD4 count <100 cells/mm³). * **Diagnosis:** Identified by **Modified Acid-Fast staining** (Kinyoun stain) showing bright red oocysts. * **Alternative:** Paromomycin (an aminoglycoside) can be used as an alternative or adjunct, though it is less effective than Nitazoxanide.

Q: Which of the following is NOT a beta-lactamase inhibitor?

Piperacillin. ### Explanation The correct answer is **Piperacillin** because it is an **extended-spectrum penicillin**, not a beta-lactamase inhibitor. **1. Why Piperacillin is the correct answer:** Piperacillin belongs to the **Antipseudomonal Penicillins** class. While it has a broad spectrum of activity against Gram-negative bacteria (including *Pseudomonas aeruginosa*), it is highly susceptible to hydrolysis by beta-lactamase enzymes produced by resistant bacteria [1]. To protect it from degradation, it is almost always administered in combination with a beta-lactamase inhibitor (e.g., Piperacillin + Tazobactam). **2. Analysis of incorrect options:** * **Sulbactam (Option A):** This is a "suicide inhibitor" of beta-lactamase. It binds irreversibly to the enzyme, preventing it from destroying the co-administered antibiotic (e.g., Ampicillin + Sulbactam). * **Clavulanic acid (Option B):** This is the classic beta-lactamase inhibitor derived from *Streptomyces clavuligerus*. It is commonly paired with Amoxicillin (Co-amoxiclav) to extend its spectrum against staphylococci and *H. influenzae*. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "Suicide Inhibitors":** Clavulanic acid, Sulbactam, and Tazobactam are structural analogs of penicillin that bind covalently to the active site of beta-lactamases [2]. * **Newer Non-Beta-lactam Inhibitors:** Be aware of **Avibactam, Relebactam, and Vaborbactam**. Unlike the older inhibitors, these do not have a beta-lactam ring and are effective against KPC (Klebsiella pneumoniae carbapenemase). * **CAST mnemonic:** To remember the classic inhibitors: **C**lavulanic acid, **A**vibactam, **S**ulbactam, **T**azobactam. * **Piperacillin's unique feature:** It is the most potent penicillin against *Pseudomonas*, but it is ineffective against MRSA.

Question 1

Which antimalarial drug can be safely administered in a baby with glucose-6-phosphate dehydrogenase deficiency?

Accepted Answer

Mefloquine

Answer

Chloroquine

Answer

Quinine

Answer

Primaquine

Question 2

Which of the following statements regarding ivermectin is true?

Accepted Answer

All the above.

Answer

It is the most effective drug for strongyloidiasis.

Answer

It is the drug of choice for onchocerciasis.

Answer

It can be used to treat scabies.

Question 3

Why are drugs used in AKT-4 kits for TB?

Accepted Answer

Decrease in resistance by mutation

Answer

None

Answer

Decrease in resistance by conjugation

Answer

To cure the disease early

Question 4

Which of the following is NOT a true statement regarding vancomycin uses?

Accepted Answer

Drug of choice for pseudomembranous enterocolitis

Answer

Surgical prophylaxis in MRSA prevalent areas

Answer

Effective in penicillin-resistant pneumococcal infection

Answer

Methicillin-resistant Staphylococcus aureus infection

Question 5

A patient requires antibiotic treatment for prosthetic valve culture-positive infective endocarditis. Their medical history includes several anaphylactic reactions to penicillin G during the past year. What is the best treatment approach?

Accepted Answer

Vancomycin

Answer

Amoxicillin clavulanic acid

Answer

Aztreonam

Answer

Cefazolin plus gentamicin

Question 6

Which of the following drugs is not used for multidrug-resistant tuberculosis (MDR-TB)?

Accepted Answer

Amikacin

Answer

Kanamycin

Answer

Levofloxacin

Answer

Ethionamide

Question 7

Which anti-HIV drug is known to cause myopathy that resembles mitochondrial myopathy with ragged red fibers?

Accepted Answer

Zidovudine

Answer

Enfuvirtide

Answer

Nevirapine

Answer

Tenofovir

Question 8

What is the drug of choice for Cryptosporidium parvum infection?

Accepted Answer

Nitazoxanide

Answer

Cotrimoxazole

Answer

Ivermectin

Answer

Diiodohydroxyquinoline

Question 9

Which of the following drugs affects neuromuscular transmission?

Accepted Answer

Streptomycin

Answer

Sulfonamide

Answer

Nitrofurantoin

Answer

Isoniazid (INH)

Question 10

Which of the following is NOT a beta-lactamase inhibitor?

Accepted Answer

Piperacillin

Answer

Sulbactam

Answer

Clavulanic acid

Answer

None of the above

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

On this page

Practice by Chapter

Want unlimited practice?