Antimicrobial Agents Practice Questions

Q: Which of the following drugs is likely to damage the eighth cranial nerve when administered for a long period of time?

Streptomycin. **Explanation:** The correct answer is **Streptomycin**. Streptomycin is an **Aminoglycoside** antibiotic used as a first-line drug in the treatment of Tuberculosis. **1. Why Streptomycin is correct:** Aminoglycosides are notorious for their **ototoxicity** and nephrotoxicity. They accumulate in the endolymph and perilymph of the inner ear, leading to the destruction of sensory hair cells. Specifically, Streptomycin is more **vestibulotoxic** than cochleotoxic, causing symptoms like vertigo, tinnitus, and loss of equilibrium due to damage to the **eighth cranial nerve (Vestibulocochlear nerve)**. **2. Why other options are incorrect:** * **Ethambutol:** Its primary dose-related toxicity is **Optic Neuritis** (damage to the second cranial nerve), leading to decreased visual acuity and red-green color blindness. * **Isoniazid (INH):** The hallmark side effect is **Peripheral Neuropathy** (due to Vitamin B6 deficiency) and hepatotoxicity. It does not typically affect the cranial nerves. * **Rifampicin:** Known for causing **orange-colored secretions** (urine, sweat, tears) and hepatotoxicity. It is a potent microsomal enzyme inducer but is not ototoxic. **NEET-PG High-Yield Pearls:** * **Mnemonic for Aminoglycoside Ototoxicity:** **S**treptomycin and **G**entamicin are primarily **Vestibulotoxic** (S-G-V), while **A**mikacin and **N**eomycin are primarily **Cochleotoxic** (A-N-C). * Streptomycin is contraindicated in pregnancy as it can cause **fetal ototoxicity** (congenital deafness). * Always monitor renal function (Creatinine) when using aminoglycosides, as nephrotoxicity often precedes or exacerbates ototoxicity.

Q: Nephrolithiasis occurs with the toxicity to which of the following drugs?

Indinavir. ### Explanation **Correct Answer: C. Indinavir** **Mechanism and Pathophysiology:** Indinavir is a Protease Inhibitor (PI) used in the treatment of HIV. The primary reason for nephrolithiasis (kidney stones) with Indinavir is its **poor solubility** in urine. Approximately 20% of the drug is excreted unchanged in the urine. At physiological urinary pH, Indinavir tends to crystallize, leading to the formation of radiolucent stones. This can manifest clinically as renal colic, hematuria, or crystalluria. To mitigate this risk, patients are strictly advised to maintain high fluid intake (at least 1.5 to 2 liters of water daily). **Analysis of Incorrect Options:** * **A. Ritonavir:** While a potent PI, it is primarily known for its role as a "pharmacokinetic booster" (inhibiting CYP3A4) and its side effects of GI distress and perioral paresthesia, rather than nephrolithiasis. * **B. Saquinavir:** This was the first PI developed. Its main adverse effects include GI upset and QT interval prolongation, but it is not associated with renal stone formation. * **D. Nelfinavir:** This drug is unique among PIs as it cannot be boosted by Ritonavir. Its most characteristic side effect is significant diarrhea, not nephrolithiasis. **High-Yield Clinical Pearls for NEET-PG:** * **Indinavir "Signature" Side Effects:** Nephrolithiasis and Hyperbilirubinemia (indirect/unconjugated). * **Protease Inhibitor Class Effects:** Metabolic syndrome (dyslipidemia, insulin resistance/hyperglycemia) and Lipodystrophy (buffalo hump/central obesity). * **Other drugs causing Nephrolithiasis:** Acetazolamide, Sulfonamides, and Triamterene. * **Management:** Indinavir-induced stones are often managed with hydration and temporary drug discontinuation; they are typically not visible on standard X-rays (radiolucent).

Q: Which of the following drugs is NOT excreted in bile?

Gentamicin. **Explanation:** The correct answer is **Gentamicin**. **1. Why Gentamicin is the correct answer:** Gentamicin is an **aminoglycoside**. Aminoglycosides are highly polar, water-soluble polycationic compounds. Due to their high water solubility and lack of metabolism, they are excreted almost exclusively by the kidneys via **glomerular filtration**. They do not undergo significant biliary excretion. This is why dosage adjustment is critical in patients with renal impairment. **2. Analysis of Incorrect Options:** * **Erythromycin (Option A):** This macrolide is primarily concentrated in the liver and excreted in the **bile** in very high concentrations. Only about 2–5% is excreted in the urine. * **Ampicillin (Option B):** While many penicillins are renally excreted, ampicillin undergoes significant **enterohepatic circulation** and is excreted in high concentrations in the bile. This makes it useful for treating biliary tract infections (e.g., cholecystitis) and typhoid carriers. * **Rifampicin (Option C):** This drug is a classic example of a drug excreted via the **biliary route**. It undergoes deacetylation in the liver and is then excreted in bile; it also induces its own metabolism (auto-induction). **3. High-Yield Clinical Pearls for NEET-PG:** * **Biliary Excreted Drugs (Mnemonic: "Ceph-A-R-E"):** **Ceph**triaxone, **A**mpicillin, **R**ifampicin, **E**rythromycin. * **Gentamicin Toxicity:** Because it is cleared renally, it is associated with **Nephrotoxicity** (Acute Tubular Necrosis) and **Ototoxicity**. * **Drug of Choice for Biliary Infections:** Ampicillin or Ceftriaxone are often preferred due to their high biliary concentration. * **Rifampicin Fact:** It imparts an orange-red discoloration to urine, sweat, and tears, but its primary route of elimination remains biliary.

Q: What is the treatment for Subacute sclerosing panencephalitis (SSPE)?

Inosine pranobex. **Explanation:** **Subacute Sclerosing Panencephalitis (SSPE)** is a rare, progressive, and fatal neurodegenerative disease caused by a persistent infection with a mutated measles virus. **Why Inosine Pranobex is Correct:** **Inosine pranobex** (also known as Methisoprinol) is the drug of choice for SSPE. It is an immunomodulatory agent that enhances T-cell function and increases the activity of natural killer cells. While it is not a cure, it has been shown to slow down the clinical progression of the disease and prolong survival in a significant number of patients. In clinical practice, it is often used in combination with intrathecal or intraventricular **Interferon-alpha**. **Analysis of Incorrect Options:** * **Abacavir (Option A):** This is a Nucleoside Reverse Transcriptase Inhibitor (NRTI) used in the treatment of HIV/AIDS. It has no role in treating measles-related complications. * **Glatiramer (Option C):** This is an immunomodulator used specifically for the management of Relapsing-Remitting Multiple Sclerosis (RRMS). It acts as a decoy for T-cells, preventing them from attacking myelin. * **Interferon (Option D):** While Interferon-alpha is used as an *adjunct* therapy (often administered intrathecally), **Inosine pranobex** remains the primary systemic treatment mentioned in standard pharmacological textbooks for SSPE management. **High-Yield Clinical Pearls for NEET-PG:** * **Etiology:** Occurs 5–10 years after a primary measles infection, usually in children who were infected before age 2. * **EEG Finding:** Characterized by **periodic, high-voltage slow-wave complexes** (Radermecker complexes). * **CSF Finding:** Presence of highly elevated titers of measles antibodies (**Oligoclonal bands**). * **Stages:** Progresses from behavioral changes to myoclonic jerks (Stage 2) and eventually to akinetic mutism.

Q: An 86-year-old male presents with a two-day history of cough and hemoptysis. On admission, his temperature is 103 F. Physical examination reveals rales in the right lung, and chest X-ray shows increased density in the right middle lobe. Sputum microscopy reveals numerous Gram-positive cocci, and sputum culture confirms penicillinase-producing Staphylococcus aureus. Which of the following antimicrobial agents should be administered?

Oxacillin. ### Explanation **Correct Answer: B. Oxacillin** **1. Why Oxacillin is Correct:** The patient is diagnosed with pneumonia caused by **penicillinase-producing *Staphylococcus aureus***. Penicillinase is a specific type of $\beta$-lactamase that hydrolyzes the $\beta$-lactam ring of traditional penicillins, rendering them ineffective. **Oxacillin** (along with Cloxacillin, Nafcillin, and Dicloxacillin) belongs to the class of **Penicillinase-Resistant Penicillins (Antistaphylococcal Penicillins)**. These drugs possess a bulky side chain that sterically hinders the penicillinase enzyme from reaching the $\beta$-lactam ring, making them the drug of choice for Methicillin-Susceptible *S. aureus* (MSSA). **2. Why Other Options are Incorrect:** * **A. Ampicillin:** This is an extended-spectrum penicillin. While it has better Gram-negative coverage than Penicillin G, it is highly susceptible to degradation by staphylococcal penicillinase. * **C & D. Carbenicillin and Ticarcillin:** These are **Antipseudomonal penicillins**. While they have an extended spectrum against *Pseudomonas aeruginosa*, they are not resistant to staphylococcal penicillinase and would be inactivated by this strain. **3. NEET-PG High-Yield Pearls:** * **Mechanism of Resistance:** *S. aureus* resistance to penicillin is mediated by **plasmids** carrying the *blaZ* gene (encoding penicillinase). * **MRSA Mechanism:** If a strain is resistant to Oxacillin/Methicillin (MRSA), the resistance is due to an **altered Target site** (PBP2a encoded by the *mecA* gene), not enzyme production. Vancomycin is the drug of choice for MRSA. * **Drug of Choice:** For MSSA infections, Oxacillin/Nafcillin are clinically superior to Vancomycin. * **Clinical Presentation:** Staphylococcal pneumonia often presents following a viral prodrome (e.g., post-influenza) and is characterized by a high risk of abscess formation or pneumatoceles.

Q: Isoniazid is metabolized by which process?

Acetylation. **Explanation:** **Isoniazid (INH)**, a primary drug for tuberculosis, is metabolized in the liver primarily via **Acetylation** (Phase II reaction) [1][2]. This process is catalyzed by the enzyme **N-acetyltransferase 2 (NAT2)** [1]. 1. **Why Acetylation is Correct:** Acetylation involves the transfer of an acetyl group to the drug molecule [3], making it more water-soluble for excretion. In the case of Isoniazid, it is converted into Acetyl-isoniazid [4]. This is a classic example of a Phase II metabolic pathway that determines the drug's half-life and toxicity profile [2]. 2. **Why Other Options are Incorrect:** * **Oxidation (Phase I):** While many drugs (like Phenytoin or Warfarin) undergo oxidation via Cytochrome P450 enzymes, it is not the primary pathway for Isoniazid. * **Reduction (Phase I):** This involves the addition of hydrogen or removal of oxygen (e.g., Chloramphenicol). * **Hydrolysis (Phase I):** This involves the cleavage of a chemical bond by adding water (e.g., Esters like Procaine or Amides like Lidocaine). **High-Yield Clinical Pearls for NEET-PG:** * **Genetic Polymorphism:** The rate of acetylation is genetically determined, leading to two phenotypes [1][2]: * **Fast Acetylators:** (Common in Indians/Japanese) Require higher doses; may develop **Hepatotoxicity** due to rapid formation of the metabolite acetylhydrazine [4]. * **Slow Acetylators:** (Common in Caucasians/Egyptians) Higher risk of **Peripheral Neuropathy** due to drug accumulation [1]. * **Mnemonic (Drugs metabolized by Acetylation):** **"SHIP"** — **S**ulfonamides, **H**ydralazine, **I**soniazid, **P**rocainamide. * **Drug Interaction:** Isoniazid is a potent **enzyme inhibitor**, which can increase levels of drugs like Phenytoin.

Q: Stavudine (Zerit) is prescribed to a client with human immunodeficiency virus seropositive. The nurse observes which of the following most closely while the client is taking the medication?

Gait. **Explanation:** **Stavudine (d4T)** is a Nucleoside Reverse Transcriptase Inhibitor (NRTI) used in the management of HIV [2]. The correct answer is **Gait** because the most significant dose-limiting toxicity of Stavudine is **peripheral neuropathy** [3]. 1. **Why Gait is Correct:** Stavudine frequently causes distal symmetrical peripheral neuropathy, characterized by numbness, tingling, and pain in the feet and hands [3]. As the neuropathy progresses, it leads to sensory loss and muscle weakness, significantly affecting the patient's **gait** and balance. Monitoring the patient's walking pattern is a critical nursing intervention to detect early signs of neurotoxicity. 2. **Why Other Options are Incorrect:** * **Orientation:** While some antiretrovirals (like Efavirenz) cause CNS side effects, Stavudine is not primarily associated with altered consciousness or disorientation. * **Gag Reflex:** Stavudine does not affect the cranial nerves responsible for the gag reflex (CN IX, X). * **Appetite:** While NRTIs can cause GI upset, appetite is not the specific clinical parameter used to monitor for Stavudine's hallmark toxicity (neuropathy). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Stavudine:** Remember the **"P"s**: **P**eripheral neuropathy and **P**ancreatitis [3]. * **Mechanism of Toxicity:** Stavudine (and Didanosine) inhibits **Mitochondrial DNA polymerase-gamma**, leading to mitochondrial dysfunction [1]. This is the underlying cause of both neuropathy and **Lactic Acidosis** (often accompanied by hepatic steatosis) [1]. * **Lipodystrophy:** Stavudine is strongly associated with **lipoatrophy** (loss of subcutaneous fat from the face and limbs), more so than other NRTIs [3]. * **Avoid Combination:** Stavudine should not be combined with **Zidovudine (AZT)** because they compete for the same intracellular phosphorylation pathway (antagonism) [3].

Q: Which among the following is the drug of choice for Clostridium difficile-induced colitis?

Metronidazole. **Explanation:** **Clostridium difficile-induced colitis** (Pseudomembranous colitis) typically occurs due to the overgrowth of *C. difficile* following broad-spectrum antibiotic therapy (most commonly associated with Clindamycin, Fluoroquinolones, and Cephalosporins). **Why Metronidazole is correct:** Historically, **Metronidazole** (oral) has been the first-line drug of choice for mild-to-moderate cases of *C. difficile* infection (CDI) due to its efficacy, low cost, and narrow anaerobic spectrum. It works by forming toxic free radicals that disrupt the DNA of anaerobic bacteria. **Why the other options are incorrect:** * **Gentamicin:** An Aminoglycoside that is ineffective against anaerobes (it requires oxygen for bacterial uptake) and is a known risk factor for inducing CDI. * **Ciprofloxacin:** A Fluoroquinolone that is a common inciting agent for *C. difficile* overgrowth and has no role in its treatment. * **Linezolid:** An Oxazolidinone used primarily for Gram-positive infections like MRSA and VRE; it is not indicated for CDI. **High-Yield Clinical Pearls for NEET-PG:** 1. **Updated Guidelines:** While Metronidazole is the traditional answer for exams, recent **IDSA guidelines** now prefer **Oral Vancomycin** or **Fidaxomicin** as first-line for all episodes (including mild). However, if Vancomycin is unavailable or for mild cases in resource-limited settings, Metronidazole remains the standard answer. 2. **Route of Administration:** Vancomycin must be given **orally** for CDI; intravenous Vancomycin is ineffective as it does not reach the gut lumen. 3. **Fidaxomicin:** A macrocyclic antibiotic with minimal systemic absorption and a lower rate of recurrence compared to Vancomycin. 4. **Life-threatening/Fulminant CDI:** Treated with a combination of high-dose oral Vancomycin and IV Metronidazole.

Question 1

How can aminoglycoside toxicity be decreased?

Accepted Answer

Administering the total daily dose once a day

Answer

Administering the total daily dose twice a day

Answer

Administering a low dose once a day

Answer

Administering a low dose twice a day

Question 2

Which of the following drugs is likely to damage the eighth cranial nerve when administered for a long period of time?

Accepted Answer

Streptomycin

Answer

Ethambutol

Answer

Isoniazid

Answer

Rifampicin

Question 3

Nephrolithiasis occurs with the toxicity to which of the following drugs?

Accepted Answer

Indinavir

Answer

Ritonavir

Answer

Saquinavir

Answer

Nalfinavir

Question 4

Which of the following drugs is NOT excreted in bile?

Accepted Answer

Gentamicin

Answer

Erythromycin

Answer

Ampicillin

Answer

Rifampicin

Question 5

All are true about Cotrimoxazole, except?

Accepted Answer

Trimethoprim increases absorption of Sulphamethoxazole

Answer

Resistance is delayed due to drugs in combination

Answer

Trimethoprim : Sulphamethoxazole ratio is 1:5

Answer

Similar pharmacokinetics for both components

Question 6

What is the treatment for Subacute sclerosing panencephalitis (SSPE)?

Accepted Answer

Inosine pranobex

Answer

Abacavir

Answer

Glatiramer

Answer

Interferon

Question 7

An 86-year-old male presents with a two-day history of cough and hemoptysis. On admission, his temperature is 103
F. Physical examination reveals rales in the right lung, and chest X-ray shows increased density in the right middle lobe. Sputum microscopy reveals numerous Gram-positive cocci, and sputum culture confirms penicillinase-producing Staphylococcus aureus. Which of the following antimicrobial agents should be administered?

Accepted Answer

Oxacillin

Answer

Ampicillin

Answer

Carbenicillin

Answer

Ticarcillin

Question 8

Isoniazid is metabolized by which process?

Accepted Answer

Acetylation

Answer

Oxidation

Answer

Reduction

Answer

Hydrolysis

Question 9

Stavudine (Zerit) is prescribed to a client with human immunodeficiency virus seropositive. The nurse observes which of the following most closely while the client is taking the medication?

Accepted Answer

Gait

Answer

Orientation

Answer

Gag reflex

Answer

Appetite

Question 10

Which among the following is the drug of choice for Clostridium difficile-induced colitis?

Accepted Answer

Metronidazole

Answer

Gentamicin

Answer

Ciprofloxacin

Answer

Linezolid

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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