Antimicrobial Agents Practice Questions

Q: Which of the following drugs acts through inhibition of the integrase activity of the virus?

Raltegravir. **Explanation:** The question tests your knowledge of **Antiretroviral Therapy (ART)** classification based on the HIV life cycle. **Correct Option: A. Raltegravir** Raltegravir is an **Integrase Strand Transfer Inhibitor (INSTI)**. Its mechanism of action involves binding to and inhibiting the viral enzyme **integrase**. This enzyme is responsible for inserting (integrating) the HIV viral DNA into the host cell's genome. By blocking this step, the virus cannot replicate. Other drugs in this class include Dolutegravir and Elvitegravir. **Incorrect Options:** * **B. Tipranavir:** This is a **Protease Inhibitor (PI)**. It inhibits the viral protease enzyme, preventing the cleavage of polyproteins into functional mature proteins, resulting in the production of immature, non-infectious virions. * **C. Enfuvirtide:** This is a **Fusion Inhibitor**. It binds to the **gp41** subunit of the viral envelope protein, preventing the fusion of the HIV membrane with the host CD4 cell membrane. * **D. Etravirine:** This is a **Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI)**. It binds directly to the reverse transcriptase enzyme at a site different from the active site (allosteric inhibition), preventing the conversion of viral RNA to DNA. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for INSTIs:** All drugs in this class contain **"-tegra-"** (Integrase), e.g., Ral**tegra**vir, Dolu**tegra**vir. * **Dolutegravir** is currently the preferred first-line agent in WHO and NACO guidelines due to its high genetic barrier to resistance. * **Raltegravir** is known for causing an increase in **creatine kinase** and potential myopathy. * **Maraviroc** (another entry inhibitor) acts by blocking the **CCR5 receptor** on the host cell, unlike Enfuvirtide which acts on the virus.

Q: Which of the following drugs is effective against Pseudomonas infection?

Colistin. **Explanation:** **Pseudomonas aeruginosa** is a notorious Gram-negative pathogen known for its intrinsic resistance to many standard antibiotics. **Why Colistin is Correct:** Colistin (Polymyxin E) is a rapidly bactericidal drug that acts like a detergent, disrupting the outer cell membrane of Gram-negative bacteria [1]. It is considered a **"last-resort" antibiotic** specifically reserved for multidrug-resistant (MDR) Gram-negative infections, including *Pseudomonas aeruginosa*, *Acinetobacter*, and *Klebsiella pneumoniae* [1]. Due to its significant nephrotoxicity and neurotoxicity, it is used primarily when other safer anti-pseudomonal agents fail. **Why the other options are incorrect:** * **Ampicillin:** An amino-penicillin that is effective against certain Gram-positive and some Gram-negative organisms (like *E. coli*), but it is completely inactivated by the beta-lactamases produced by *Pseudomonas*. * **Ceftriaxone:** A 3rd-generation cephalosporin. While it has broad Gram-negative coverage, it notably **lacks activity** against *Pseudomonas*. (Note: Ceftazidime and Cefoperazone are the only 3rd-gen cephalosporins with anti-pseudomonal activity). * **Cefixime:** An oral 3rd-generation cephalosporin primarily used for respiratory and urinary tract infections; it has no clinical efficacy against *Pseudomonas*. **High-Yield Clinical Pearls for NEET-PG:** * **Anti-pseudomonal Penicillins:** Piperacillin, Ticarcillin. * **Anti-pseudomonal Cephalosporins:** Ceftazidime (3rd gen), Cefoperazone (3rd gen), Cefepime (4th gen). * **Carbapenems:** Imipenem, Meropenem, and Doripenem (Note: **Ertapenem** does NOT cover Pseudomonas). * **Fluoroquinolones:** Ciprofloxacin and Levofloxacin are the only oral options. * **Monobactams:** Aztreonam. * **Aminoglycosides:** Amikacin, Gentamicin, and Tobramycin.

Q: What is the drug of choice for preventing fetal toxoplasmosis infection during pregnancy?

Spiramycin. **Explanation:** The management of toxoplasmosis in pregnancy depends on whether the fetus has been infected. **Spiramycin** is the drug of choice for **preventing** vertical transmission from the mother to the fetus. **1. Why Spiramycin is correct:** Spiramycin is a macrolide antibiotic that achieves high concentrations in the **placenta**. It does not cross the placental barrier in significant amounts, meaning it treats the mother and "clears" the placenta of parasites, thereby preventing the transmission to the fetus. It is safe to use throughout pregnancy. **2. Why the other options are incorrect:** * **Pyrimethamine (A) & Sulfadiazine (B):** These drugs are folic acid antagonists [1]. Pyrimethamine is potentially **teratogenic** (especially in the first trimester) and can cause bone marrow suppression. * **Pyrimethamine + Sulfadiazine (D):** This combination is the **treatment of choice** only if fetal infection is **confirmed** (via amniotic fluid PCR or ultrasound findings). Unlike Spiramycin, these drugs cross the placenta to treat the fetus directly. They are typically administered after the 18th week of gestation along with Folinic acid (Leucovorin) to prevent maternal toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad of Congenital Toxoplasmosis:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Spiramycin:** Used for prophylaxis (prevention of transmission). * **Pyrimethamine + Sulfadiazine + Folinic Acid:** Used for confirmed fetal infection or neonatal disease. * **Alternative:** Clindamycin can be used in patients allergic to Sulfonamides.

Q: What is the drug of choice for gonococcal and non-gonococcal urethritis?

Azithromycin. **Explanation:** The correct answer is **Azithromycin**. **Why Azithromycin is the Correct Choice:** Urethritis is often "mixed," involving both *Neisseria gonorrhoeae* (gonococcal) and *Chlamydia trachomatis* (non-gonococcal). Azithromycin, a macrolide, is highly effective against *Chlamydia*. While cephalosporins (like Ceftriaxone) are typically the first-line treatment for Gonorrhea, Azithromycin is frequently co-administered to cover potential Chlamydial infection and to combat increasing gonococcal resistance. In many syndromic management protocols (like the WHO and NACO guidelines), a single 1g dose of Azithromycin is a cornerstone for treating uncomplicated urethritis. **Analysis of Incorrect Options:** * **Clindamycin (A):** This lincosamide is primarily used for anaerobic infections and Gram-positive cocci (like MRSA). It has no significant activity against *N. gonorrhoeae* or *C. trachomatis*. * **Cefepime (B):** This is a 4th-generation cephalosporin with broad-spectrum activity, including *Pseudomonas*. While it has Gram-negative coverage, it is not the standard of care for urethritis; 3rd-generation Ceftriaxone is the preferred cephalosporin for Gonorrhea. * **Metronidazole (C):** This is an antiprotozoal and anaerobic agent. It is the drug of choice for *Trichomonas vaginalis* or Bacterial Vaginosis, but it does not cover the primary bacterial causes of urethritis. **High-Yield Clinical Pearls for NEET-PG:** * **Syndromic Management (NACO):** For urethral discharge (Grey Kit), the treatment is a single dose of **Azithromycin (1g)** plus **Cefixime (400mg)**. * **Mechanism:** Azithromycin inhibits bacterial protein synthesis by binding to the **50S ribosomal subunit**. * **Chlamydia Treatment:** If Azithromycin is not used, **Doxycycline** (100mg BID for 7 days) is the alternative first-line agent for non-gonococcal urethritis.

Q: Which of the following is the drug of choice for invasive aspergillosis?

Voriconazole. **Explanation:** **Voriconazole** is the current **drug of choice (DOC)** for invasive aspergillosis. This recommendation is based on clinical trials demonstrating that voriconazole provides superior efficacy and better survival rates compared to conventional Amphotericin B, along with a more favorable safety profile. **Mechanism of Action:** Voriconazole is a second-generation triazole that inhibits the enzyme **14-α-demethylase**, thereby blocking the synthesis of ergosterol, a vital component of the fungal cell membrane. **Analysis of Options:** * **Voriconazole (Option A):** Correct. It is the primary treatment for most forms of invasive aspergillosis. * **Posaconazole (Option B):** While highly effective against *Aspergillus*, it is primarily used for **prophylaxis** in immunocompromised patients (e.g., neutropenic patients) or as salvage therapy when first-line agents fail. * **Amphotericin B (Option C):** Previously the gold standard, it is now considered an alternative (specifically the Liposomal formulation) due to significant nephrotoxicity and lower efficacy compared to voriconazole. * **Caspofungin (Option D):** An echinocandin used as salvage therapy or in combination for refractory cases; it is not used as monotherapy for initial treatment. **High-Yield Clinical Pearls for NEET-PG:** * **Side Effects of Voriconazole:** Distinctive **visual disturbances** (photopsia/blurring) occur in ~30% of patients. It is also associated with photosensitivity dermatitis and hepatic enzyme elevation. * **Alternative DOC:** **Isavuconazole** is another first-line agent for invasive aspergillosis, often preferred if the patient has renal impairment or if there is a suspicion of co-infection with Mucormycosis. * **DOC for Allergic Bronchopulmonary Aspergillosis (ABPA):** Oral **Itraconazole** (along with corticosteroids).

Q: What is the drug of choice for uncomplicated cystitis?

Fosfomycin. **Explanation:** The drug of choice for **uncomplicated cystitis** (lower urinary tract infection in non-pregnant women) has shifted in recent years due to increasing resistance patterns. **Fosfomycin** (single 3g dose) and **Nitrofurantoin** are now considered first-line agents. **Why Fosfomycin is correct:** Fosfomycin is a bactericidal antibiotic that inhibits cell wall synthesis by inhibiting the enzyme **enolpyruvate transferase (MurA)**. It is highly effective against common uropathogens, including *E. coli* and *E. faecalis*. Its primary advantage is its unique pharmacokinetic profile: a single oral dose achieves high concentrations in the urine that remain therapeutic for up to 48–72 hours, ensuring high patient compliance. **Why other options are incorrect:** * **Amoxicillin:** No longer used empirically for UTIs due to high rates of resistance among *E. coli* strains. It is only used if the organism is known to be susceptible. * **Chloramphenicol:** Primarily used for enteric fever or bacterial meningitis (in specific cases). It is not indicated for UTIs due to its significant toxicity profile (e.g., bone marrow suppression). * **Cotrimoxazole:** Previously a first-line drug, it is now reserved for cases where local resistance rates are known to be low (<20%). Widespread resistance has diminished its utility as a primary choice. **NEET-PG High-Yield Pearls:** * **Mechanism of Action:** Fosfomycin inhibits the first step of peptidoglycan synthesis (conversion of NAG to NAM). * **Pregnancy:** Both Fosfomycin and Nitrofurantoin are generally considered safe in pregnancy (Category B), though Nitrofurantoin should be avoided at term. * **Nitrofurantoin Note:** It is ineffective in pyelonephritis (upper UTI) because it does not achieve therapeutic concentrations in the renal parenchyma.

Q: Which antibiotic accentuates the neuromuscular blockade produced by pancuronium?

Streptomycin. The correct answer is **Streptomycin**. **1. Why Streptomycin is correct:** Aminoglycosides (like Streptomycin, Gentamicin, and Neomycin) are well-known for their ability to produce neuromuscular blockade [2]. They act by two primary mechanisms: * **Presynaptic:** They inhibit the release of Acetylcholine (ACh) from the motor nerve terminal by competing with Calcium ions at the voltage-gated calcium channels [2]. * **Postsynaptic:** They reduce the sensitivity of the nicotinic ACh receptors at the motor endplate. When administered with non-depolarizing neuromuscular blockers like **Pancuronium**, aminoglycosides act synergistically, significantly prolonging and intensifying the muscle paralysis [1]. This effect can be partially reversed by Calcium gluconate or Neostigmine [1]. **2. Why the other options are incorrect:** * **Erythromycin:** While Macrolides are potent enzyme inhibitors (CYP450), they do not possess intrinsic neuromuscular blocking properties. * **Penicillin G:** Beta-lactams primarily act on cell wall synthesis and do not interfere with the neuromuscular junction. * **Chloramphenicol:** This drug inhibits bacterial protein synthesis (50S subunit) but does not affect calcium channels or ACh release at the motor endplate. **3. High-Yield Clinical Pearls for NEET-PG:** * **Order of Potency for NM Blockade:** Neomycin > Streptomycin > Amikacin > Gentamicin. * **Contraindication:** Aminoglycosides are strictly contraindicated in patients with **Myasthenia Gravis** as they can precipitate a severe myasthenic crisis. * **Other drugs that potentiate NM blockers:** Magnesium salts, Calcium channel blockers, Volatile anesthetics (Isoflurane), and Quinidine. * **Management:** Intravenous **Calcium Gluconate** is the preferred treatment to antagonize aminoglycoside-induced blockade.

Q: Disulfiram-like reaction is commonly caused by which of the following?

Metronidazole. **Explanation:** **Metronidazole** is the correct answer because it inhibits the enzyme **aldehyde dehydrogenase**. Under normal conditions, alcohol is metabolized into acetaldehyde, which is then converted into acetic acid by aldehyde dehydrogenase. When this enzyme is inhibited, acetaldehyde accumulates in the blood, leading to a "Disulfiram-like reaction." [2] Symptoms include intense flushing, tachycardia, palpitations, nausea, vomiting, and hypotension. Patients must be advised to avoid alcohol during and for at least 48–72 hours after completing metronidazole therapy. **Analysis of Incorrect Options:** * **A. Penicillin:** These are beta-lactam antibiotics that inhibit cell wall synthesis. They are not associated with alcohol metabolism interference. * **C. Tetracycline:** These inhibit the 30S ribosomal subunit. While they have several side effects (e.g., photosensitivity, teeth discoloration), they do not cause disulfiram-like reactions. * **D. Erythromycin:** A macrolide that inhibits the 50S subunit. It is a potent CYP450 inhibitor but does not affect aldehyde dehydrogenase. [1] **Clinical Pearls for NEET-PG:** * **Other drugs causing Disulfiram-like reactions:** * **Cephalosporins:** Specifically those containing the **Methylthiotetrazole (MTT) side chain** (e.g., Cefotetan, Cefoperazone, Cefamandole). * **Sulfonylureas:** First-generation agents like Chlorpropamide. * **Others:** Procarbazine (anticancer), Griseofulvin (antifungal), and Tinidazole. * **Mnemonic:** "Many Compounds Can Cause Terrible Reactions" (Metronidazole, Chlorpropamide, Cephalosporins, Cefotetan, Tinidazole, Retinoids/Griseofulvin).

Question 1

Which of the following drugs acts through inhibition of the integrase activity of the virus?

Accepted Answer

Raltegravir

Answer

Tipranavir

Answer

Enfuvirtide

Answer

Etravirine

Question 2

Which of the following drugs is effective against Pseudomonas infection?

Accepted Answer

Colistin

Answer

Ampicillin

Answer

Ceftriaxone

Answer

Cefixime

Question 3

What is the drug of choice for preventing fetal toxoplasmosis infection during pregnancy?

Accepted Answer

Spiramycin

Answer

Pyrimethamine

Answer

Sulfadiazine

Answer

Pyrimethamine + Sulfadiazine

Question 4

If a patient develops resistance to isoniazid, to which drug will they simultaneously develop resistance?

Accepted Answer

Rifampicin

Answer

Streptomycin

Answer

Ethambutol

Answer

Pyrazinamide

Question 5

What is the drug of choice for gonococcal and non-gonococcal urethritis?

Accepted Answer

Azithromycin

Answer

Clindamycin

Answer

Cefepime

Answer

Metronidazole

Question 6

Which of the following is the drug of choice for invasive aspergillosis?

Accepted Answer

Voriconazole

Answer

Posaconazole

Answer

Amphotericin B

Answer

Caspofungin

Question 7

What is the drug of choice for uncomplicated cystitis?

Accepted Answer

Fosfomycin

Answer

Amoxicillin

Answer

Chloramphenicol

Answer

Cotrimoxazole

Question 8

Which antibiotic accentuates the neuromuscular blockade produced by pancuronium?

Accepted Answer

Streptomycin

Answer

Erythromycin

Answer

Penicillin G

Answer

Chloramphenicol

Question 9

Disulfiram-like reaction is commonly caused by which of the following?

Accepted Answer

Metronidazole

Answer

Penicillin

Answer

Tetracycline

Answer

Erythromycin

Question 10

Which of the following statements is true regarding Atazanavir?

Accepted Answer

Resistance is due to mutation in codon 50 isoleucine to valine substitution

Answer

Effective against only HIV-1

Answer

Decreases cholesterol and triglyceride levels

Answer

Combination with ritonavir has no advantage

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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