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 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: A 55-year-old patient with disseminated tuberculosis is prescribed antitubercular drugs. Which of the following adverse effects might be seen in a patient receiving regular intramuscular injections of streptomycin?

Deafness. **Explanation:** Streptomycin is an **Aminoglycoside** antibiotic used as a first-line drug in the treatment of Tuberculosis (though its use is now limited due to the availability of oral alternatives). **1. Why Deafness is Correct:** Aminoglycosides are notorious for their **ototoxicity** and **nephrotoxicity**. Streptomycin specifically targets the 8th cranial nerve (Vestibulocochlear nerve). It accumulates in the endolymph and perilymph of the inner ear, leading to the destruction of sensory hair cells. While it is more commonly associated with **vestibular damage** (vertigo, ataxia), it also causes **cochlear damage**, resulting in permanent sensorineural hearing loss or deafness. **2. Why Incorrect Options are Wrong:** * **A. Blindness:** This is a classic side effect of **Ethambutol**, which causes optic neuritis (decreased visual acuity and red-green color blindness). * **B. Increased AST levels:** Hepatotoxicity (elevated liver enzymes) is a common side effect of **Isoniazid (INH), Rifampin, and Pyrazinamide**, but not Streptomycin. * **C. Impotence:** This is not a recognized side effect of any standard first-line antitubercular drugs. **Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Streptomycin inhibits bacterial protein synthesis by binding to the **30S ribosomal subunit**, causing mRNA misreading. * **Contraindication:** It is **teratogenic** (causes fetal ototoxicity) and is the only first-line ATT drug contraindicated in pregnancy. * **Excretion:** It is excreted unchanged by the kidneys; hence, dosage adjustment is vital in renal failure to prevent toxicity. * **Mnemonic for ATT Side Effects:** **E**thambutol (**E**ye), **S**treptomycin (**S**ound/Ears), **I**NH (**I**soniazid - **I**njures Nerves/Liver).

Q: Which of the following drugs is NOT commonly used against enteric fever?

Amikacin. **Explanation:** Enteric fever (Typhoid) is caused by *Salmonella typhi* and *S. paratyphi*, which are **intracellular** pathogens. Effective treatment requires drugs that can achieve high concentrations within cells and the biliary tract. **Why Amikacin is the correct answer:** Amikacin is an **Aminoglycoside**. Aminoglycosides are polar molecules that are poorly lipid-soluble; consequently, they have **poor intracellular penetration**. Furthermore, they are primarily effective against aerobic extracellular gram-negative bacilli and lack clinical efficacy against *Salmonella* species in the context of enteric fever. Therefore, they are not used in its management. **Why the other options are incorrect:** * **Ciprofloxacin (Fluoroquinolone):** Historically the drug of choice due to excellent intracellular penetration and high biliary concentration. However, its use is now limited in many regions due to rising Nalidixic acid resistance (NARST). * **Ceftriaxone (3rd Gen Cephalosporin):** Currently the **drug of choice** for empirical treatment of complicated or multidrug-resistant (MDR) enteric fever. It is administered parenterally. * **Azithromycin (Macrolide):** An excellent oral alternative for uncomplicated typhoid, especially in cases of fluoroquinolone resistance, due to its massive intracellular accumulation and long half-life. **High-Yield Clinical Pearls for NEET-PG:** 1. **Drug of Choice (Empirical):** Ceftriaxone. 2. **Best Oral Drug (for MDR strains):** Azithromycin. 3. **Carrier State:** The drug of choice to eradicate the chronic carrier state (in the gallbladder) is **Ciprofloxacin** (for 4–6 weeks) or Ampicillin. 4. **Historical Context:** Chloramphenicol was the first drug of choice but is now obsolete due to resistance and bone marrow toxicity.

Q: A pregnant patient at 20 weeks gestation presents with fever and dysuria, leading to a preliminary diagnosis of cystitis. Which of the following antibiotics is safe to use for this patient?

Amoxicillin. **Explanation:** **Correct Answer: D. Amoxicillin** **Why Amoxicillin is correct:** Amoxicillin is a penicillin-group antibiotic and is classified as **FDA Pregnancy Category B**. It is considered safe and effective for treating Urinary Tract Infections (UTIs) in pregnancy because it does not cross the placental barrier in harmful concentrations and lacks teratogenic potential. In pregnant patients, asymptomatic bacteriuria and cystitis must be treated promptly to prevent progression to pyelonephritis, which is associated with preterm labor. **Why the other options are incorrect:** * **A. Ciprofloxacin:** Fluoroquinolones are generally avoided in pregnancy (Category C) as they have a high affinity for bone and cartilage, potentially causing **arthropathy** and permanent cartilage damage in the developing fetus. * **B. Gentamicin:** Aminoglycosides are associated with **ototoxicity** (damage to the 8th cranial nerve) and potential nephrotoxicity in the fetus. They are reserved for life-threatening infections like severe pyelonephritis where no safer alternative exists. * **C. Cotrimoxazole:** This is a combination of Sulfamethoxazole and Trimethoprim. Trimethoprim is a **folate antagonist** (risk of neural tube defects in the 1st trimester), and Sulfonamides can displace bilirubin from albumin, leading to **kernicterus** in the newborn if used near term. **NEET-PG High-Yield Pearls:** * **Drug of Choice for UTI in Pregnancy:** Nitrofurantoin (avoided only at term/near labor due to risk of neonatal hemolysis) or Amoxicillin/Cephalosporins. * **Safe Antibiotics (Category B):** Penicillins, Cephalosporins, Erythromycin (except estolate form), and Azithromycin. * **Teratogenic mnemonic:** "**T**atty **C**ats **A**re **G**reedy" (**T**etracycline - stained teeth; **C**hloramphenicol - Gray baby syndrome; **A**minoglycosides - Ototoxicity; **G**luoroquinolones - Cartilage damage).

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

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 4

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 5

What is the drug of choice for Cryptosporidium parvum infection?

Accepted Answer

Nitazoxanide

Answer

Cotrimoxazole

Answer

Ivermectin

Answer

Diiodohydroxyquinoline

Question 6

Which of the following drugs affects neuromuscular transmission?

Accepted Answer

Streptomycin

Answer

Sulfonamide

Answer

Nitrofurantoin

Answer

Isoniazid (INH)

Question 7

A 55-year-old patient with disseminated tuberculosis is prescribed antitubercular drugs. Which of the following adverse effects might be seen in a patient receiving regular intramuscular injections of streptomycin?

Accepted Answer

Deafness

Answer

Blindness

Answer

Increased AST levels

Answer

Impotence

Question 8

Which of the following drugs is NOT commonly used against enteric fever?

Accepted Answer

Amikacin

Answer

Ciprofloxacin

Answer

Ceftriaxone

Answer

Azithromycin

Question 9

An 82-year-old hospitalized patient with creatinine clearance of 25 mL/min has a microbial infection requiring treatment with antibiotics. Which one of the following drugs is least likely to require a dosage adjustment, either a smaller dose than usual or an increased interval between doses?

Accepted Answer

Erythromycin

Answer

Amphotericin B

Answer

Gentamicin

Answer

Imipenem-cilastatin

Question 10

A pregnant patient at 20 weeks gestation presents with fever and dysuria, leading to a preliminary diagnosis of cystitis. Which of the following antibiotics is safe to use for this patient?

Accepted Answer

Amoxicillin

Answer

Ciprofloxacin

Answer

Gentamicin

Answer

Cotrimoxazole

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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