Antimicrobial Agents Practice Questions

Q: Which of the following drugs is known to cause ototoxicity?

Streptomycin. **Explanation:** **Streptomycin** is the correct answer because it belongs to the **Aminoglycoside** class of antibiotics, which are notorious for their dose-dependent and duration-dependent **ototoxicity** [2], [3]. Aminoglycosides accumulate in the perilymph and endolymph of the inner ear, leading to the destruction of sensory hair cells [1], [3]. Streptomycin, specifically, is more **vestibulotoxic** (causing vertigo, ataxia, and loss of balance) than cochleotoxic [2], [4], though it can cause permanent hearing loss. **Analysis of Incorrect Options:** * **Vancomycin (Option A):** While often cited in older literature as ototoxic, modern purified preparations of Vancomycin rarely cause ototoxicity when used alone. It typically only increases the risk of hearing loss when administered concurrently with other ototoxic drugs (like aminoglycosides or loop diuretics). * **Ampicillin (Option C):** This is a penicillin-group antibiotic. Its primary adverse effects are hypersensitivity reactions (rashes, anaphylaxis) and diarrhea; it has no known association with ototoxicity. * **Rifampicin (Option D):** An anti-tubercular drug primarily known for causing orange-red discoloration of body fluids (urine, sweat, tears) and hepatotoxicity. It does not affect the auditory or vestibular systems. **High-Yield Clinical Pearls for NEET-PG:** * **Aminoglycoside Mnemonic:** Remember that **S**treptomycin and **G**entamicin are primarily **Vestibulotoxic**, while **A**mikacin, **K**anamycin, and **N**eomycin are primarily **Cochleotoxic** [4]. * **Synergy:** The risk of ototoxicity increases significantly when aminoglycosides are combined with **Loop Diuretics** (e.g., Furosemide, Ethacrynic acid). * **Genetic Predisposition:** Patients with the **m.1555A>G mutation** in mitochondrial DNA are at a significantly higher risk of permanent aminoglycoside-induced deafness, even with a single dose.

Q: Time-dependent killing is exhibited by all the following drugs except:

Gentamicin. ### Explanation The pharmacodynamics of antimicrobial agents are categorized based on whether their efficacy depends on the **duration of exposure** or the **peak concentration** achieved. **Why Gentamicin is the correct answer:** Gentamicin is an **Aminoglycoside**. Aminoglycosides, along with Fluoroquinolones and Daptomycin, exhibit **Concentration-dependent killing**. This means their bactericidal activity increases as the peak serum concentration ($C_{max}$) exceeds the Minimum Inhibitory Concentration (MIC) of the pathogen. These drugs also possess a significant **Post-Antibiotic Effect (PAE)**, allowing for once-daily (extended-interval) dosing. **Why the other options are incorrect:** * **Ceftriaxone (Cephalosporin) & Meropenem (Carbapenem):** Both belong to the **Beta-lactam** family. Beta-lactams are classic examples of **Time-dependent killers**. Their efficacy depends on the percentage of time the drug concentration remains above the MIC ($T > MIC$). Increasing the concentration far above the MIC does not increase the rate of killing. * **Vancomycin (Glycopeptide):** Vancomycin is primarily considered a time-dependent killer (specifically $AUC/MIC$ ratio dependent). It requires maintained therapeutic levels over time to ensure bacterial eradication. **High-Yield Clinical Pearls for NEET-PG:** 1. **Time-dependent ($T > MIC$):** Beta-lactams (Penicillins, Cephalosporins, Carbapenems), Linezolid, and Erythromycin. 2. **Concentration-dependent ($C_{max}/MIC$):** Aminoglycosides, Fluoroquinolones, Metronidazole, and Amphotericin B. 3. **Post-Antibiotic Effect (PAE):** This is the persistent suppression of bacterial growth after the drug level falls below the MIC. It is most pronounced with Aminoglycosides against Gram-negative bacteria. 4. **Dosing Strategy:** For time-dependent drugs, frequent dosing or continuous infusion is preferred; for concentration-dependent drugs, large single daily doses are often more effective and less toxic.

Q: Ivermectin is indicated in which of the following conditions?

All of the above. **Explanation:** Ivermectin is a broad-spectrum antiparasitic agent derived from *Streptomyces avermitilis*. It works by binding to **glutamate-gated chloride channels** in invertebrate nerve and muscle cells, leading to hyperpolarization, paralysis, and death of the parasite. **Why "All of the above" is correct:** * **Scabies (Option A):** Ivermectin is the drug of choice for **crusted (Norwegian) scabies** and is used as a highly effective oral alternative to topical permethrin for classical scabies. * **Intestinal Nematodes (Option B):** It is the **drug of choice for Strongyloidiasis** (*Strongyloides stercoralis*). It is also effective against *Ascaris lumbricoides*, *Enterobius vermicularis*, and *Trichuris trichiura*. * **Filariasis (Option C):** Ivermectin is the drug of choice for **Onchocerciasis** (River Blindness) as it kills the microfilariae. It is also used in the mass drug administration (MDA) programs for **Lymphatic Filariasis** (often in combination with Albendazole). **High-Yield Clinical Pearls for NEET-PG:** 1. **Mechanism of Action:** Potentiates GABA-mediated neurotransmission and opens glutamate-gated chloride channels. 2. **Mazzotti Reaction:** A severe inflammatory response (fever, rash, joint pain) seen after treating Onchocerciasis with Ivermectin due to the rapid killing of microfilariae. 3. **Contraindication:** It should not be used in patients with a breached blood-brain barrier (e.g., meningitis, African Sleeping Sickness) because it can cross into the CNS and cause toxicity, as human GABA receptors are located in the brain. 4. **Drug of Choice Summary:** Remember Ivermectin for **S.O.S.** — **S**trongyloidiasis, **O**nchocerciasis, and **S**cabies (Crusted).

Q: In leprosy, which is considered the most effective bactericidal agent?

Rifampicin. ### Explanation **Rifampicin** is the most potent bactericidal drug available for the treatment of leprosy. It acts by inhibiting the DNA-dependent RNA polymerase of *Mycobacterium leprae*. Its bactericidal activity is so profound that a single dose of 600 mg can kill more than 99.9% of viable bacilli within 3-7 days. Because of this rapid action, it renders the patient non-infectious very quickly, making it the backbone of Multi-Drug Therapy (MDT). **Analysis of Incorrect Options:** * **Dapsone (Option B):** While it is the oldest and most widely used drug for leprosy, it is primarily **bacteriostatic**. It works by inhibiting the enzyme dihydropteroate synthase (folate synthesis). Resistance develops easily if used as monotherapy. * **Clofazimine (Option A):** This is a dye that has weak **bacteriostatic** and anti-inflammatory properties. It is included in MDT primarily to prevent dapsone resistance and to control Type 2 Lepra reactions (ENL). * **Ethionamide (Option D):** This is a secondary drug used only as an alternative in cases of resistance or intolerance to standard MDT. It is less effective and more toxic than Rifampicin. **High-Yield Clinical Pearls for NEET-PG:** * **MDT Regimen (WHO):** * **Paucibacillary (PB):** Rifampicin + Dapsone for 6 months. * **Multibacillary (MB):** Rifampicin + Dapsone + Clofazimine for 12 months. * **Side Effects:** Dapsone can cause **hemolysis** (especially in G6PD deficiency) and "Dapsone Syndrome." Clofazimine causes **reddish-black skin discoloration** and ichthyosis. * **Drug of Choice for Type 2 Lepra Reaction:** Thalidomide (or Corticosteroids). * **Drug of Choice for Type 1 Lepra Reaction:** Corticosteroids (Prednisolone).

Q: Besides zidovudine and lamivudine, which of the following drugs is a reverse transcriptase inhibitor used in the treatment of HIV infection?

Abacavir. The treatment of HIV involves **Highly Active Antiretroviral Therapy (HAART)**, which utilizes different classes of drugs targeting specific stages of the viral life cycle. **1. Why Abacavir is Correct:** Abacavir belongs to the **Nucleoside Reverse Transcriptase Inhibitors (NRTIs)** class. Like Zidovudine and Lamivudine, it acts as a competitive inhibitor of the viral enzyme **Reverse Transcriptase**. It is a guanosine analogue that incorporates itself into the growing viral DNA chain, causing premature chain termination. [2] **2. Why the Other Options are Incorrect:** * **Saquinavir, Indinavir, and Ritonavir (Options A, B, D):** These drugs belong to the **Protease Inhibitors (PIs)** class. They work by inhibiting the viral protease enzyme, which is responsible for cleaving precursor polyproteins into functional mature proteins [1]. This results in the production of immature, non-infectious virions. **High-Yield Clinical Pearls for NEET-PG:** * **Abacavir Hypersensitivity:** A critical side effect of Abacavir is a potentially fatal hypersensitivity reaction. It is strongly associated with the **HLA-B*5701** allele. Screening for this allele is mandatory before starting the drug. * **Ritonavir Boosting:** Ritonavir is a potent inhibitor of the **CYP3A4** enzyme [1]. In clinical practice, it is often used in low doses to "boost" the plasma concentrations of other protease inhibitors rather than for its own antiviral effect. * **NRTI Class Side Effects:** The most common class-wide side effect of NRTIs is **lactic acidosis** due to mitochondrial toxicity. * **Zidovudine (AZT):** Frequently tested for causing **macrocytic anemia** and bone marrow suppression.

Q: Which of the following drugs is contraindicated in liver dysfunction?

Pefloxacin. **Explanation:** The correct answer is **Pefloxacin**. **1. Why Pefloxacin is the correct answer:** Pefloxacin is a fluoroquinolone that is unique because it undergoes extensive **hepatic metabolism** (primarily via N-demethylation to norfloxacin). Unlike most other fluoroquinolones (like Ciprofloxacin or Levofloxacin) which are primarily excreted by the kidneys, Pefloxacin is eliminated mainly by the liver. In patients with liver dysfunction, its clearance is significantly reduced, leading to drug accumulation and increased risk of toxicity. Therefore, it is contraindicated or requires extreme caution in hepatic failure. **2. Why the other options are incorrect:** * **Vancomycin:** This glycopeptide is primarily excreted unchanged by the **kidneys**. It requires dose adjustment in renal failure, not liver failure. * **Amikacin:** As an aminoglycoside, it is highly polar and excreted entirely by **glomerular filtration**. It is nephrotoxic and ototoxic but does not depend on hepatic metabolism. * **Hydralazine:** While metabolized by the liver (acetylation), it is not contraindicated in liver dysfunction, though dose monitoring may be required. It is a classic cause of drug-induced Lupus. **3. NEET-PG High-Yield Pearls:** * **Fluoroquinolones & Excretion:** Most are renally excreted. **Pefloxacin and Moxifloxacin** are the notable exceptions that are primarily metabolized/excreted by the liver. * **Mnemonic for Liver-Excreted Drugs:** Remember "**D**on't **C**ause **M**ore **L**iver **P**roblems" — **D**oxycycline, **C**eftriaxone, **M**oxifloxacin/Macrolides, **L**incosamides (Clindamycin), **P**efloxacin. * **Safe in Renal Failure:** These drugs are often preferred in patients with kidney disease because they do not require renal dose adjustment.

Q: Which fluoroquinolone has the least oral bioavailability?

Norfloxacin. **Explanation:** The correct answer is **Norfloxacin (Option A)**. **1. Why Norfloxacin is correct:** Bioavailability refers to the fraction of an administered drug that reaches the systemic circulation in an unchanged form. Among the fluoroquinolones, **Norfloxacin** has the poorest oral absorption, with a bioavailability of only **30–50%**. Because of this low systemic concentration, it is not used for respiratory or systemic infections. Instead, its use is primarily restricted to **Urinary Tract Infections (UTIs)** and infectious diarrhea, where high concentrations in the urine and gut are beneficial. **2. Why the other options are incorrect:** * **Ofloxacin (Option B):** Has excellent oral bioavailability, typically exceeding **95%**. It is well-absorbed and reaches high systemic concentrations. * **Ciprofloxacin (Option C):** Has a moderate to good bioavailability of approximately **70%**. While lower than Levofloxacin, it is significantly higher than Norfloxacin. * **Levofloxacin (Option D):** Known for its "near-perfect" bioavailability of approximately **99%**. This allows for a 1:1 transition between oral and intravenous dosing (sequential therapy). **3. NEET-PG High-Yield Pearls:** * **Bioavailability Trend:** Levofloxacin (99%) > Ofloxacin (95%) > Ciprofloxacin (70%) > Norfloxacin (35%). * **Food/Cation Interaction:** All fluoroquinolones exhibit reduced absorption when taken with antacids (Al, Mg), iron, or calcium due to **chelation**. * **Excretion:** Most fluoroquinolones are renally excreted; however, **Moxifloxacin** is primarily excreted via the liver and does not require dose adjustment in renal failure (but cannot be used for UTIs). * **Mechanism:** They inhibit **DNA Gyrase** (Gram-negative) and **Topoisomerase IV** (Gram-positive).

Q: What is the drug of choice for hepatitis B?

Tenofovir. **Explanation:** The management of Chronic Hepatitis B (CHB) focuses on the long-term suppression of HBV DNA replication to prevent cirrhosis and hepatocellular carcinoma. **Why Tenofovir is the Correct Answer:** **Tenofovir** (specifically Tenofovir Disoproxil Fumarate or Tenofovir Alafenamide) and **Entecavir** [2] are the first-line oral antiviral agents (Nucleoside/Nucleotide Analogue Reverse Transcriptase Inhibitors) for Hepatitis B. Tenofovir is preferred due to its **high genetic barrier to resistance**, potent antiviral efficacy, and favorable safety profile [3]. Unlike older drugs like Lamivudine, resistance to Tenofovir is clinically negligible even after years of therapy [3]. **Analysis of Incorrect Options:** * **A. Beta interferon:** While Peginterferon **alpha**-2a is a treatment option for HBV [1], Beta interferon is primarily used in the management of Multiple Sclerosis. * **B. Sofosbuvir:** This is a NS5B polymerase inhibitor used exclusively for **Hepatitis C** (HCV) [3]. It has no clinical role in treating HBV. * **C. Simeprevir:** This is a second-generation protease inhibitor used in the treatment of **Hepatitis C** (HCV) genotype 1. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Tenofovir or Entecavir are the preferred oral agents. * **Pregnancy:** Tenofovir is the DOC for treating HBV in pregnant women to prevent vertical transmission (Category B). * **HIV Co-infection:** Tenofovir is a component of ART and is ideal for patients co-infected with HBV and HIV. * **Side Effects:** Monitor for nephrotoxicity and decreased bone mineral density with Tenofovir Disoproxil Fumarate (TDF). Tenofovir Alafenamide (TAF) has better bone and renal safety.

Q: Which of the following drugs does NOT act against HIV-2?

Efavirenz. **Explanation:** The correct answer is **Efavirenz**. The fundamental concept here is the structural difference between the Reverse Transcriptase (RT) enzymes of HIV-1 and HIV-2. **Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs)**, such as Efavirenz, Nevirapine, and Delavirdine, bind to a specific hydrophobic pocket on the HIV-1 RT enzyme. HIV-2 lacks this specific binding site, making it **intrinsically resistant** to all first-generation NNRTIs. **Analysis of Options:** * **Efavirenz (Option C):** As an NNRTI, it is ineffective against HIV-2. This is a high-yield distinction because HIV-2 infections must be treated with regimens that exclude NNRTIs. * **Ritonavir (Option A):** This is a Protease Inhibitor (PI). Most PIs are active against both HIV-1 and HIV-2, though HIV-2 may show reduced sensitivity to some (e.g., Amprenavir). * **Tenofovir (Option B) & Zalcitabine (Option D):** These are Nucleoside/Nucleotide Reverse Transcriptase Inhibitors (NRTIs). NRTIs act as competitive inhibitors and chain terminators for the RT enzyme in both HIV-1 and HIV-2. **NEET-PG High-Yield Pearls:** 1. **HIV-2 Resistance Profile:** Naturally resistant to **NNRTIs** and **Enfuvirtide** (Fusion Inhibitor). 2. **Drugs of Choice for HIV-2:** Usually includes a backbone of two NRTIs plus an Integrase Inhibitor (INSTI) or a boosted Protease Inhibitor (e.g., Lopinavir/r or Darunavir/r). 3. **Monitoring:** HIV-2 cannot be monitored using standard HIV-1 viral load assays; specific HIV-2 DNA/RNA PCR tests are required.

Q: Fluconazole is more effective than itraconazole in which of the following systemic fungal diseases?

Cryptococcal meningitis. The primary reason **Fluconazole** is more effective than Itraconazole in **Cryptococcal meningitis** is its superior pharmacokinetic profile regarding the Central Nervous System (CNS) [2]. 1. **Why Option B is correct:** Fluconazole is a small, water-soluble molecule with low protein binding, allowing it to achieve **excellent cerebrospinal fluid (CSF) penetration** (reaching 60–90% of serum levels) [1], [2]. Itraconazole, conversely, is highly lipophilic, protein-bound, and has negligible CSF penetration [2]. While Amphotericin B + Flucytosine is the induction therapy of choice [3], Fluconazole is the drug of choice for **maintenance/suppression therapy** in Cryptococcal meningitis. 2. **Why other options are incorrect:** * **Histoplasmosis (A), Blastomycosis (C), and Sporotrichosis (D):** These are caused by dimorphic fungi. **Itraconazole** is the preferred agent for mild-to-moderate infections of this type because it has a broader spectrum of activity and higher intrinsic potency against these specific pathogens compared to Fluconazole [4]. Fluconazole is generally considered a second-line or alternative agent for these conditions due to lower efficacy. **High-Yield Clinical Pearls for NEET-PG:** * **Fluconazole Spectrum:** Excellent for *Candida albicans* and *Cryptococcus*, but has **no activity** against *Aspergillus* or Mucormycosis. * **Resistance:** *Candida krusei* is intrinsically resistant to Fluconazole; *Candida glabrata* shows dose-dependent resistance. * **Itraconazole:** Drug of choice for Histoplasmosis, Blastomycosis, Sporotrichosis, and Chromoblastomycosis. It requires an acidic gastric environment for optimal absorption. * **Side Effect:** All azoles inhibit CYP450 enzymes, but Fluconazole has the least effect on hepatic microsomal enzymes compared to Ketoconazole or Itraconazole.

Question 1

Which of the following drugs is known to cause ototoxicity?

Accepted Answer

Streptomycin

Answer

Vancomycin

Answer

Ampicillin

Answer

Rifampicin

Question 2

Time-dependent killing is exhibited by all the following drugs except:

Accepted Answer

Gentamicin

Answer

Ceftriaxone

Answer

Vancomycin

Answer

Meropenem

Question 3

Ivermectin is indicated in which of the following conditions?

Accepted Answer

All of the above

Answer

Scabies

Answer

Intestinal nematode infection

Answer

Filariasis

Question 4

In leprosy, which is considered the most effective bactericidal agent?

Accepted Answer

Rifampicin

Answer

Clofazimine

Answer

Dapsone

Answer

Ethionamide

Question 5

Besides zidovudine and lamivudine, which of the following drugs is a reverse transcriptase inhibitor used in the treatment of HIV infection?

Accepted Answer

Abacavir

Answer

Saquinavir

Answer

Indinavir

Answer

Ritonavir

Question 6

Which of the following drugs is contraindicated in liver dysfunction?

Accepted Answer

Pefloxacin

Answer

Vancomycin

Answer

Amikacin

Answer

Hydralazine

Question 7

Which fluoroquinolone has the least oral bioavailability?

Accepted Answer

Norfloxacin

Answer

Ofloxacin

Answer

Ciprofloxacin

Answer

Levofloxacin

Question 8

What is the drug of choice for hepatitis B?

Accepted Answer

Tenofovir

Answer

Beta interferon

Answer

Sofosbuvir

Answer

Simeprevir

Question 9

Which of the following drugs does NOT act against HIV-2?

Accepted Answer

Efavirenz

Answer

Ritonavir

Answer

Tenofovir

Answer

Zalcitabine

Question 10

Fluconazole is more effective than itraconazole in which of the following systemic fungal diseases?

Accepted Answer

Cryptococcal meningitis

Answer

Pulmonary histoplasmosis

Answer

Non-meningeal blastomycosis

Answer

Disseminated sporotrichosis

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

On this page

Practice by Chapter

Want unlimited practice?