Anti-infective Agents — MCQs
Which antifungal binds to ergosterol, causing fungal cell membrane damage?
An ICU patient is suffering from Rhinovirus infection. How do we treat the patient?
Herpetic keratitis is treated by which of the following?
Which of the following drugs does not inhibit bacterial protein synthesis?
Which of the following is not a treatment option for vernal keratoconjunctivitis?
Idoxuridine is used for treatment of?
Which of the following is not a contraindication for neuraxial block?
Which route is most preferred for Endophthalmitis treatment?
Which of the following is a Category A bioterrorism agent?
Which of the following drugs possesses similar cycloplegic action and is a more potent mydriatic than atropine?
Anti-infective Agents Indian Medical PG Practice Questions and MCQs
Question 1: Which antifungal binds to ergosterol, causing fungal cell membrane damage?
- A. Caspofungin
- B. Terbinafine
- C. Fluconazole
- D. Amphotericin B (Correct Answer)
Explanation: Amphotericin B - **Amphotericin B** is a polyene antifungal that directly binds to **ergosterol**, the primary sterol in fungal cell membranes [2]. - This binding creates pores in the membrane, leading to leakage of intracellular components and ultimately **fungal cell death** [2]. Caspofungin - **Caspofungin** is an echinocandin, which inhibits the synthesis of **β-(1,3)-D-glucan**, a vital component of the fungal cell wall. - Its mechanism of action is distinct from ergosterol binding and primarily targets cell wall integrity rather than the cell membrane directly. Terbinafine - **Terbinafine** is an allylamine antifungal that inhibits **squalene epoxidase**, an enzyme involved in ergosterol synthesis. - By blocking this enzyme, it prevents the formation of ergosterol, leading to an accumulation of toxic squalene and disrupting membrane function, but it does not directly bind to ergosterol. Fluconazole - **Fluconazole** is an azole antifungal that inhibits **lanosterol 14-α-demethylase**, a cytochrome P450 enzyme responsible for an earlier step in ergosterol synthesis [1]. - This action prevents ergosterol production, impairing membrane function, but it does not involve direct binding to pre-existing ergosterol [1].
Question 2: An ICU patient is suffering from Rhinovirus infection. How do we treat the patient?
- A. Piperacillin + Tazobactam + Azithromycin
- B. Clarithromycin
- C. Cephalosporin + Ganciclovir
- D. Supportive care only (Correct Answer)
Explanation: ***Supportive care only*** - **Rhinovirus** is a common cause of the **common cold**, and there is no specific antiviral treatment available for it. [1] - Management focuses on alleviating symptoms such as fever, congestion, and cough to ensure patient comfort and prevent secondary complications, especially in an ICU setting. *Piperacillin + Tazobactam + Azithromycin* - This combination is a broad-spectrum antibiotic regimen (piperacillin/tazobactam is an extended-spectrum penicillin, and azithromycin is a macrolide) targeting bacterial infections. [2] - **Rhinovirus is a virus**, and antibiotics are ineffective against viral infections, making this an inappropriate treatment. *Clarithromycin* - **Clarithromycin** is a macrolide antibiotic primarily used to treat bacterial infections, such as respiratory tract infections caused by **atypical bacteria** or community-acquired pneumonia. [2] - It has no activity against **Rhinovirus**, a common cold virus. *Cephalosporin + Ganciclovir* - **Cephalosporins** are a class of beta-lactam antibiotics used for various bacterial infections. [2] - **Ganciclovir** is an antiviral agent specifically used to treat **cytomegalovirus (CMV)** infections, not Rhinovirus.
Question 3: Herpetic keratitis is treated by which of the following?
- A. Analgesics
- B. Atropine
- C. Steroids
- D. Acyclovir (Correct Answer)
Explanation: ***Acyclovir*** - **Acyclovir** is an **antiviral agent** that specifically targets the **herpes simplex virus**, which is the causative agent of herpetic keratitis. - It works by inhibiting viral DNA replication, thereby reducing viral load and preventing further damage to the cornea. *Analgesics* - **Analgesics** are used to manage pain but do not address the **viral etiology** of herpetic keratitis. - While they can improve patient comfort, they are not a definitive treatment for the underlying infection. *Atropine* - **Atropine** is a **cycloplegic agent** used to paralyze the ciliary muscle and dilate the pupil, often to reduce pain from ciliary spasms in uveitis. - It does not have **antiviral properties** and is not effective against the herpes virus. *Steroids* - **Corticosteroids** can suppress inflammation but are generally **contraindicated** in active herpetic keratitis, especially in the epithelial form. - They can worsen the viral infection by compromising the immune response, potentially leading to **corneal ulceration** and perforation.
Question 4: Which of the following drugs does not inhibit bacterial protein synthesis?
- A. Aminoglycosides
- B. Chloramphenicol
- C. Clindamycin
- D. Sulfonamides (Correct Answer)
Explanation: ***Sulfonamides*** - Sulfonamides do **NOT** inhibit bacterial protein synthesis; instead, they inhibit **folic acid synthesis**. - They act as **competitive inhibitors** of dihydropteroate synthase, an enzyme involved in the synthesis of dihydrofolic acid. - Folic acid is essential for nucleotide synthesis and DNA replication, making sulfonamides bacteriostatic agents that work through a completely different mechanism than protein synthesis inhibitors. *Aminoglycosides* - Aminoglycosides bind to the **30S ribosomal subunit**, causing misreading of mRNA and premature termination of protein synthesis. - This leads to the production of **abnormal and non-functional proteins**, ultimately killing the bacterial cell. *Chloramphenicol* - Chloramphenicol binds to the **50S ribosomal subunit**, thereby inhibiting the peptidyl transferase enzyme. - This prevents the formation of **peptide bonds** between amino acids, effectively blocking protein elongation. *Clindamycin* - Clindamycin also binds to the **50S ribosomal subunit**, specifically at the P-site. - It interferes with the **translocation step** of protein synthesis, preventing ribosomal movement along the mRNA.
Question 5: Which of the following is not a treatment option for vernal keratoconjunctivitis?
- A. Steroids
- B. Chromaglycate
- C. Olopatadine
- D. Antibiotics (Correct Answer)
Explanation: ***Antibiotics*** - **Vernal keratoconjunctivitis (VKC)** is a non-infectious, **allergic inflammatory condition** of the conjunctiva. - Antibiotics are primarily used to treat bacterial infections and have **no direct role** in the management of VKC. *Steroids* - **Topical corticosteroids** (e.g., prednisolone, loteprednol, fluorometholone) are a mainstay of VKC treatment, especially for severe cases and acute exacerbations. - They significantly reduce inflammation and associated symptoms by **suppressing the immune response**. *Chromaglycate* - **Sodium cromoglycate** is a **mast cell stabilizer** commonly used in the treatment of VKC. - It works by preventing the degranulation of mast cells, thereby **inhibiting the release of inflammatory mediators** like histamine. *Olopatadine* - **Olopatadine** is a dual-acting medication that functions as both an **antihistamine** and a **mast cell stabilizer**. - It provides rapid relief from itching and other allergic symptoms by blocking histamine receptors and stabilizing mast cells.
Question 6: Idoxuridine is used for treatment of?
- A. Influenza
- B. RSV
- C. HSV (Correct Answer)
- D. HIV
Explanation: ***HSV*** - **Idoxuridine** is a **pyrimidine analog** that inhibits viral DNA synthesis, making it effective against **herpes simplex virus (HSV)** infections, particularly **herpes keratitis** (ophthalmic use). - Its mechanism involves being incorporated into viral DNA, leading to errors in replication and transcription. - It is applied **topically** for ocular HSV infections due to systemic toxicity concerns. *Influenza* - **Idoxuridine** is not active against **influenza viruses**. - **Antiviral drugs** like **oseltamivir** or **zanamivir** are typically used for influenza treatment. *RSV* - **Idoxuridine** is not indicated for the treatment of **respiratory syncytial virus (RSV)**. - **Ribavirin** is the primary antiviral agent used for severe RSV infections, especially in immunocompromised patients. *HIV* - **Idoxuridine** has no significant activity against **human immunodeficiency virus (HIV)**. - **Antiretroviral therapy (ART)**, a combination of drugs targeting various stages of the HIV life cycle, is used for HIV treatment.
Question 7: Which of the following is not a contraindication for neuraxial block?
- A. Patient on clopidogrel
- B. Patient on antihypertensive medication (Correct Answer)
- C. Local infection
- D. Platelet count < 50,000
Explanation: ***Patient on antihypertensive medication*** - Antihypertensive medications are generally **not a contraindication** for neuraxial block; however, careful management of **blood pressure** especially following the sympathetic block is essential. - The primary concern is **hypotension** due to the sympathetic blockade, which can be managed with fluids and vasopressors, not an absolute contraindication. *Patient on clopidogrel* - **Clopidogrel** is an **antiplatelet agent** that increases the risk of **spinal hematoma** if a neuraxial block is performed. - This medication should typically be discontinued for a specific period before neuraxial procedures to minimize bleeding risk. *Local infection* - Performing a neuraxial block through an infected area increases the risk of introducing **pathogens into the subarachnial space**, leading to severe complications like **meningitis** or an **epidural abscess**. - This is an **absolute contraindication** to protect against central nervous system infection. *Platelet count < 50,000* - A **low platelet count** indicates impaired hemostasis, significantly increasing the risk of **bleeding** and the formation of a **spinal hematoma** following neuraxial puncture. - While exact thresholds vary, a platelet count below 50,000 is generally considered an **absolute contraindication** for neuraxial anesthesia.
Question 8: Which route is most preferred for Endophthalmitis treatment?
- A. Oral antibiotic
- B. Intravenous antibiotic
- C. Topical antibiotic
- D. Intravitreal antibiotic (Correct Answer)
Explanation: ***Intravitreal antibiotic*** - **Intravitreal injection** directly delivers a high concentration of antibiotics into the **vitreous cavity**, which is essential for treating intraocular infections like endophthalmitis. - This route bypasses protective barriers like the **blood-retinal barrier**, ensuring therapeutic drug levels reach the infection site promptly and effectively. *Oral antibiotic* - **Oral antibiotics** have poor penetration into the **vitreous humor** due to the **blood-retinal barrier**, making them generally ineffective as a sole therapy for endophthalmitis. - They may be used as an adjunct in some cases but cannot achieve the high local concentrations needed to resolve severe intraocular infections. *Intravenous antibiotic* - Similar to oral antibiotics, **intravenous antibiotics** struggle to penetrate the **blood-retinal barrier** adequately to achieve therapeutic concentrations in the vitreous humor for endophthalmitis. - While they can be administered in severe cases, they do not provide the direct, high-dose delivery needed to control the infection within the eye as effectively as intravitreal injections. *Topical antibiotic* - **Topical antibiotics** primarily reach the ocular surface and anterior segment of the eye, with very limited penetration into the **vitreous cavity**. - They are generally ineffective for treating endophthalmitis, which is an infection of the inner eye, and are typically reserved for superficial ocular infections.
Question 9: Which of the following is a Category A bioterrorism agent?
- A. Brucella
- B. Q fever
- C. Typhus fever
- D. Anthrax (Correct Answer)
Explanation: ***Anthrax*** - **Anthrax**, caused by *Bacillus anthracis*, is classified as a **Category A** bioterrorism agent due to its high mortality rate, ease of dissemination, and potential for major public health impact. - It can manifest as cutaneous, inhalational, gastrointestinal, or injectional forms, with **inhalational anthrax** being the most lethal. *Brucella* - **Brucella** species cause brucellosis, which is classified as a **Category B** bioterrorism agent. - While it can be debilitating, it generally has a lower mortality rate and less public health impact than Category A agents. *Q fever* - **Q fever**, caused by *Coxiella burnetii*, is another **Category B** bioterrorism agent. - It causes a flu-like illness and can have chronic complications but is not as severe or easily disseminated as Category A agents. *Typhus fever* - **Typhus fever**, caused by *Rickettsia prowazekii* (epidemic typhus) or *Rickettsia typhi* (murine typhus), is a **Category B** bioterrorism agent. - It can cause severe illness but is not among the highest-priority agents like anthrax, smallpox, or botulism.
Question 10: Which of the following drugs possesses similar cycloplegic action and is a more potent mydriatic than atropine?
- A. Hyoscine (Correct Answer)
- B. Tropicamide
- C. Homatropine
- D. All of the above
Explanation: **Explanation:** The correct answer is **Hyoscine (Scopolamine)**. **Why Hyoscine is the correct answer:** Hyoscine is a belladonna alkaloid that acts as a competitive antagonist at muscarinic receptors. In terms of ocular potency, it is significantly more potent than atropine on a weight-for-weight basis. While it produces a **similar degree of cycloplegia** (paralysis of the ciliary muscle), it is a **more potent mydriatic** (pupillary dilator) than atropine. Its duration of action (3–7 days) is shorter than that of atropine (7–10 days), making it a useful alternative when a potent but slightly shorter-acting cycloplegic is required. **Analysis of Incorrect Options:** * **Tropicamide:** This is the shortest-acting mydriatic (duration 4–6 hours). While it is excellent for fundus examination, its cycloplegic action is much weaker and shorter than atropine. * **Homatropine:** A semi-synthetic derivative that is 10 times less potent than atropine. It has a shorter duration of action (1–3 days) and is primarily used in the treatment of anterior uveitis to prevent synechiae without the prolonged blurriness of atropine. **High-Yield Clinical Pearls for NEET-PG:** * **Potency Order:** Hyoscine > Atropine > Homatropine. * **Duration of Action (Cycloplegia):** Atropine (7–10 days) > Hyoscine (3–7 days) > Homatropine (1–3 days) > Cyclopentolate (24 hours) > Tropicamide (6 hours). * **Drug of Choice:** Atropine is the drug of choice for refraction in children <5 years (due to strong accommodation), while Homatropine/Cyclopentolate is preferred for older children. * **Side Effect:** Systemic absorption of atropine in children can lead to "Atropine flushing," fever, and tachycardia.
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