Antimicrobial Agents — MCQs

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?

Q858Easy

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

Q859Medium

What is the dose-limiting toxicity of amphotericin B?

Q860Easy

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

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 851: Which anti-tuberculosis drug can cause hyperuricemia?

A. Isoniazid
B. Pyrazinamide (Correct Answer)
C. Streptomycin
D. Rifampicin

Explanation: **Explanation:** **Pyrazinamide (PZA)** is the correct answer because it is well-known for causing **hyperuricemia**. The underlying mechanism involves its active metabolite, **pyrazinoic acid**, which inhibits the renal secretion of uric acid by competing for the URAT-1 transporter in the proximal convoluted tubules. This leads to decreased excretion and elevated serum uric acid levels. While most patients remain asymptomatic, it can occasionally precipitate **acute gouty arthritis**. **Analysis of Incorrect Options:** * **Isoniazid (INH):** Its primary adverse effects are peripheral neuropathy (prevented by Vitamin B6) and hepatotoxicity. It does not significantly affect uric acid levels. * **Streptomycin:** An aminoglycoside primarily associated with **ototoxicity** (vestibulocochlear nerve damage) and **nephrotoxicity**. * **Rifampicin:** Known for causing orange-red discoloration of body fluids (urine, sweat, tears) and being a potent inducer of microsomal enzymes (CYP450). **High-Yield Clinical Pearls for NEET-PG:** * **PZA and Gout:** If a patient on AKT (Anti-Koch's Treatment) develops joint pain, Pyrazinamide is the most likely culprit. * **Ethambutol Connection:** Ethambutol also causes hyperuricemia by a similar mechanism, but Pyrazinamide is more frequently associated with this side effect in exam questions. * **Hepatotoxicity:** Pyrazinamide is considered the **most hepatotoxic** drug among the first-line anti-tubercular agents. * **Sterilizing Action:** PZA is most effective against intracellular bacilli residing within acidic environments (macrophages).

Question 852: Which of the following can cause hypoglycemia in a patient of severe cerebral malaria on treatment?

A. Quinine (Correct Answer)
B. Chloroquine
C. Halofantrine
D. Mefloquine

Explanation: **Explanation:** The correct answer is **Quinine**. **Why Quinine causes Hypoglycemia:** Quinine is a potent stimulator of the **pancreatic beta cells**, leading to hyperinsulinemia. This excess insulin secretion results in profound hypoglycemia. In patients with severe cerebral malaria, this risk is compounded because the *Plasmodium falciparum* parasite itself consumes host glucose, and the patient may already be in a hypermetabolic state with depleted glycogen stores. Therefore, monitoring blood glucose levels is mandatory when administering intravenous Quinine. **Analysis of Incorrect Options:** * **Chloroquine:** While it can rarely cause hypoglycemia in overdose, it is not a characteristic side effect at therapeutic doses and is not the drug of choice for severe cerebral malaria due to widespread resistance. * **Halofantrine:** Its primary clinical concern is **cardiotoxicity** (QT interval prolongation). It does not significantly affect insulin secretion. * **Mefloquine:** Known primarily for **neuropsychiatric side effects** (vivid dreams, psychosis, seizures). It does not cause hypoglycemia. **NEET-PG High-Yield Pearls:** 1. **Drug of Choice:** For severe/complicated malaria, **Artesunate** (IV) is now the drug of choice over Quinine as it acts faster and has a better safety profile. 2. **Cinchonism:** A classic triad of Quinine toxicity involving tinnitus, deafness, and dizziness. 3. **Blackwater Fever:** A rare complication of Quinine treatment leading to massive intravascular hemolysis and hemoglobinuria. 4. **Safe in Pregnancy:** Quinine is considered safe for treating malaria in all trimesters of pregnancy.

Question 853: Oral vancomycin is indicated in which of the following conditions?

A. Bacillary dysentery
B. Campylobacter diarrhoea
C. Appendicitis
D. Antibiotic-associated pseudomembranous enterocolitis (Correct Answer)

Explanation: **Explanation:** **Vancomycin** is a glycopeptide antibiotic that is poorly absorbed from the gastrointestinal tract when administered orally [1]. While this is a disadvantage for systemic infections, it is highly advantageous for treating localized infections within the gut lumen, as the drug reaches high concentrations in the feces. 1. **Why Option D is Correct:** **Antibiotic-associated pseudomembranous enterocolitis** is caused by an overgrowth of *Clostridium difficile* (C. diff), usually following broad-spectrum antibiotic use. Oral vancomycin is a first-line treatment (alongside Fidaxomicin) because it remains in the gut to act directly on the bacteria [1]. Note: Intravenous vancomycin is ineffective for *C. difficile* as it does not cross the intestinal barrier into the lumen. 2. **Why Incorrect Options are Wrong:** * **A & B (Bacillary dysentery/Campylobacter):** These are invasive enteric infections caused by *Shigella* and *Campylobacter jejuni*, respectively. They require systemic antibiotics that achieve good tissue penetration, such as Fluoroquinolones (Ciprofloxacin) or Macrolides (Azithromycin). * **C (Appendicitis):** This is a surgical emergency often involving polymicrobial aerobic and anaerobic flora. It requires systemic (IV) antibiotics like Ceftriaxone plus Metronidazole. **High-Yield Clinical Pearls for NEET-PG:** * **Red Man Syndrome:** A common side effect of rapid **IV** vancomycin infusion due to direct histamine release (not a true IgE allergy). * **Drug of Choice (DOC):** Oral Vancomycin is the DOC for severe *C. difficile* infections. * **Spectrum:** Vancomycin is active only against **Gram-positive** organisms (MRSA, Enterococci) [1], [2]. * **Mechanism:** Inhibits bacterial cell wall synthesis by binding to the **D-Ala-D-Ala** terminus of nascent peptidoglycan.

Question 854: Which of the following is a nucleotide reverse transcriptase inhibitor?

A. Indinavir
B. Nelfinavir
C. Tenofovir (Correct Answer)
D. Lopinavir

Explanation: **Explanation:** **Tenofovir** is the correct answer because it is a **Nucleotide Reverse Transcriptase Inhibitor (NtRTI)**. Unlike Nucleoside Reverse Transcriptase Inhibitors (NRTIs) like Zidovudine or Abacavir, which require three steps of phosphorylation to become active, Tenofovir is already a monophosphate (nucleotide). It only requires two additional phosphorylation steps by host cell kinases to become Tenofovir diphosphate. Once active, it competes with natural deoxyadenosine triphosphate for incorporation into viral DNA, causing **premature chain termination** of the HIV DNA strand. **Analysis of Incorrect Options:** * **Indinavir, Nelfinavir, and Lopinavir (Options A, B, and D):** These drugs belong to the **Protease Inhibitors (PIs)** class. They work by inhibiting the viral enzyme protease (HIV-1 protease), preventing the cleavage of gag-pol polyproteins into mature, functional proteins. This results in the production of immature, non-infectious virions. A common suffix for this class is **"-navir."** **High-Yield Clinical Pearls for NEET-PG:** * **Tenofovir** is unique because it is the only NtRTI used in HAART and is also highly effective against the **Hepatitis B Virus (HBV)**. * **Adverse Effects:** Tenofovir is associated with **nephrotoxicity** (Fanconi syndrome) and a decrease in **bone mineral density**. * **Mnemonic for PIs:** "Never (Navir) tease a protease." * **Drug of Choice:** Tenofovir + Lamivudine + Dolutegravir (TLD regimen) is currently the preferred first-line ART regimen globally.

Question 855: Which of the following antibiotics is considered safe to use during pregnancy?

A. Aminoglycosides
B. Penicillin (Correct Answer)
C. Cotrimoxazole
D. Ciprofloxacin

Explanation: **Explanation:** **Penicillin** is the correct answer because it belongs to the **FDA Pregnancy Category B**. These drugs are considered safe because they do not interfere with mammalian cell processes; their mechanism of action (inhibition of bacterial cell wall synthesis) targets a structure absent in human cells. Penicillins and Cephalosporins are the first-line choices for most bacterial infections during pregnancy. **Why the other options are incorrect:** * **Aminoglycosides (e.g., Gentamicin, Streptomycin):** These are contraindicated due to the risk of **ototoxicity** and nephrotoxicity in the fetus. Streptomycin, specifically, is associated with 8th cranial nerve damage (congenital deafness). * **Cotrimoxazole:** This is a combination of Sulfamethoxazole and Trimethoprim. It is avoided because 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. * **Ciprofloxacin (Fluoroquinolones):** These are avoided in pregnancy because they have a high affinity for growing bone and cartilage, potentially causing **arthropathy** and permanent cartilage damage in the fetus. **High-Yield Clinical Pearls for NEET-PG:** * **Safe in Pregnancy (Mnemonic: "P-C-E"):** **P**enicillins, **C**ephalosporins, **E**rythromycin (except the Estolate form, which causes cholestatic hepatitis in the mother). * **Teratogenic Antibiotics (Mnemonic: "FAST"):** **F**luoroquinolones (Cartilage), **A**minoglycosides (Ototoxicity), **S**ulfonamides (Kernicterus), **T**etracyclines (Discolored teeth/Bone hypoplasia). * **Nitrofurantoin** is safe for UTIs in pregnancy but should be avoided at term due to the risk of hemolytic anemia in newborns with G6PD deficiency.

Question 856: What is the recommended drug for chemoprophylaxis of plague?

A. Streptomycin
B. Erythromycin
C. Tetracycline (Correct Answer)
D. Vancomycin

Explanation: **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.

Question 857: 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?

A. Chloramphenicol
B. Cycloheximide
C. Erythromycin (Correct Answer)
D. Puromycin

Explanation: ### 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.

Question 858: A permanent staining of teeth in infants may be produced due to the administration of which of the following medications during pregnancy?

A. Tetracyclines (Correct Answer)
B. Chloramphenicol
C. Erythromycin
D. Amoxycillin

Explanation: **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.

Question 859: What is the dose-limiting toxicity of amphotericin B?

A. Infusion-related reactions
B. Renal tubular acidosis (Correct Answer)
C. Myelosuppression
D. Hypotension

Explanation: **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).

Question 860: Which of the following drugs can be used in the treatment of both Human Immunodeficiency Virus (HIV) and Hepatitis B virus (HBV) infection?

A. Enfuvirtide
B. Emtricitabine (Correct Answer)
C. Abacavir
D. Acyclovir

Explanation: **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.

Practice by Chapter

Beta-Lactam Antibiotics

Practice Questions

Aminoglycosides

Practice Questions

Macrolides and Ketolides

Practice Questions

Tetracyclines

Practice Questions

Quinolones

Practice Questions

Sulfonamides and Trimethoprim

Practice Questions

Antimycobacterial Drugs

Practice Questions

Antifungal Agents

Practice Questions

Antiviral Drugs

Practice Questions

Antiparasitic Agents

Practice Questions

Principles of Antimicrobial Selection

Practice Questions

Antimicrobial Resistance

Practice Questions

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