Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1501: Anti-HIV drug used for prevention of vertical transmission?

A. Nevirapine (Correct Answer)
B. Lamivudine
C. Efavirenz
D. Tenofovir

Explanation: ***Nevirapine*** - **Nevirapine** is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that was historically used in resource-limited settings for the prevention of **mother-to-child transmission (MTCT)** of HIV. - A single dose of **nevirapine** given to the mother during labor and to the neonate within 72 hours of birth was shown to significantly reduce the risk of **vertical transmission** (HIVNET 012 trial) [1]. - **Historical significance**: This was a landmark approach in the early 2000s when resources were limited. - **Current practice note**: Modern guidelines (WHO, 2023+) now recommend **combination antiretroviral therapy (cART)** for all pregnant women with HIV, rather than single-dose nevirapine, due to superior efficacy and reduced resistance risk [1]. *Lamivudine* - **Lamivudine** is a nucleoside reverse transcriptase inhibitor (NRTI) that is **part of current combination therapy regimens** for prevention of mother-to-child transmission. - It is not used alone but is a component of **cART regimens** recommended in modern PMTCT protocols. - In the historical context of this question, it was not the single-agent answer being sought. *Efavirenz* - **Efavirenz** is an NNRTI now used in HIV treatment regimens for pregnant women in current PMTCT protocols. - Previous concerns about first-trimester teratogenicity have been re-evaluated, and it is included in WHO-recommended regimens [1]. - However, in the context of single-drug prophylaxis (historical approach), nevirapine was preferred. *Tenofovir* - **Tenofovir** is a nucleotide reverse transcriptase inhibitor (NtRTI) and is the **backbone of current first-line cART regimens** for pregnant women with HIV. - It is highly effective as part of combination therapy for PMTCT. - It was not used as a single-dose prophylactic agent in the historical context of this question.

Question 1502: Which antifungal can be used orally but not intravenously?

A. Voriconazole
B. Amphotericin B
C. Griseofulvin (Correct Answer)
D. None of the options

Explanation: ***Griseofulvin*** - **Griseofulvin** is an oral antifungal agent primarily used for dermatophyte infections [2], and it is **not available** or administered intravenously. - Its mechanism involves binding to **keratin** in newly forming skin, hair, and nails, preventing fungal invasion. *Voriconazole* - **Voriconazole** is a broad-spectrum triazole antifungal that is available in both **oral and intravenous** formulations [1]. - It is often used for invasive aspergillosis and other serious fungal infections [2]. *Amphotericin B* - **Amphotericin B** is a potent antifungal agent administered **intravenously** for severe systemic fungal infections [2]. - It has **poor oral bioavailability** and is not absorbed from the gastrointestinal tract, making it unsuitable for oral systemic therapy. - Oral formulations exist only for **local treatment** of GI candidiasis, not for systemic infections. *None of the options* - This option is incorrect because **griseofulvin** fits the description of being an antifungal that can be used orally but not intravenously.

Question 1503: What is the drug of choice for MRSA infection?

A. Ciprofloxacin
B. Oxacillin
C. Vancomycin (Correct Answer)
D. Clindamycin

Explanation: ***Vancomycin*** - **Vancomycin** is the **drug of choice** for **methicillin-resistant Staphylococcus aureus (MRSA)** infections due to its activity against the resistant strain. - It works by inhibiting cell wall synthesis, targeting the **D-Ala-D-Ala** precursor in peptidoglycan. *Ciprofloxacin* - **Ciprofloxacin** is a **fluoroquinolone antibiotic** that is generally ineffective against **MRSA**. - MRSA strains are typically **resistant to ciprofloxacin** and other fluoroquinolones. *Oxacillin* - **Oxacillin** is a **beta-lactam antibiotic** in the penicillin family, specifically used for **methicillin-sensitive Staphylococcus aureus (MSSA)** infections. - It is **ineffective against MRSA** because MRSA possesses the *mecA* gene, encoding an altered penicillin-binding protein (PBP2a) that renders beta-lactams inactive. *Clindamycin* - **Clindamycin** can be used for **MRSA infections**, but it is generally reserved for **milder localized infections** or in specific cases based on susceptibility testing. - Its use often requires **D-test** to rule out **inducible clindamycin resistance**, which can lead to treatment failure.

Question 1504: Colistin is obtained from ?

A. Bacteria (Correct Answer)
B. Fungi
C. Herbs
D. Actinomycetes

Explanation: ***Bacteria*** - Colistin, also known as **polymyxin E**, is an antibiotic derived from the bacterium **Bacillus polymyxa subspecies colistinus** (now reclassified as *Paenibacillus polymyxa*). - It works by disrupting the **outer membrane** of Gram-negative bacteria, making it effective against multi-drug resistant strains. - While actinomycetes are also bacteria, in pharmacology, antibiotics from **Bacillus species** are categorized separately from actinomycete-derived drugs. *Fungi* - Many common antibiotics, such as **penicillin** and **cephalosporins**, are derived from fungi (e.g., *Penicillium*, *Cephalosporium*), but colistin is not one of them. - Fungal-derived antibiotics typically target bacterial **cell wall synthesis** or **protein synthesis**. *Actinomycetes* - **Actinomycetes**, particularly from the *Streptomyces* genus, are a rich source of antibiotics, including **streptomycin**, **tetracyclines**, and **erythromycin**. - While actinomycetes are technically bacteria, they are classified separately in pharmacology due to their unique characteristics and prolific antibiotic production. - Colistin is specifically produced by **Bacillus species**, not actinomycetes. *Herbs* - Herbs are used for traditional medicine and can have various therapeutic properties, but they do **not produce antibiotics** like colistin. - While some plant-derived compounds have antimicrobial activity, colistin is a product of **microbial fermentation**.

Question 1505: What is the mechanism of action of Daclizumab in immunology?

A. IL 2 receptor blocker (Correct Answer)
B. Activation of cGMP pathway
C. Inhibition of adenylate cyclase
D. Blockade of IL-10 receptor

Explanation: ***IL 2 receptor blocker*** - Daclizumab is a **monoclonal antibody** that specifically targets the **CD25 subunit** of the **interleukin-2 (IL-2) receptor** on T-lymphocytes. - By blocking this receptor, Daclizumab prevents IL-2 from binding, thereby inhibiting T-cell activation and proliferation, which is useful in preventing **transplant rejection** and treating **multiple sclerosis**. *Activation of cGMP pathway* - The cGMP pathway is commonly associated with the actions of **nitric oxide** and **natriuretic peptides**, affecting smooth muscle relaxation and cellular signaling. - This mechanism is **unrelated** to the immunomodulatory effects of Daclizumab, which primarily acts on T-cell activation. *Inhibition of adenylate cyclase* - **Adenylate cyclase** inhibition typically leads to a decrease in **cyclic AMP (cAMP)** levels, affecting various cellular processes including hormone signaling and neurotransmission. - This mechanism is not the primary mode of action for Daclizumab, which is designed to modulate the immune response via the IL-2 receptor. *Blockade of IL-10 receptor* - **IL-10** is an **anti-inflammatory cytokine** that suppresses immune responses, and blocking its receptor would theoretically enhance inflammation. - Daclizumab's mechanism is centered on inhibiting **pro-inflammatory T-cell activation** by blocking IL-2 signaling, not by interfering with IL-10 pathways.

Question 1506: Which of the following drugs is not recommended for the treatment of P. falciparum malaria?

A. Artemether
B. Doxycycline
C. Ciprofloxacin (Correct Answer)
D. Quinine

Explanation: ***Ciprofloxacin*** - **Ciprofloxacin** is an antibiotic that is not effective against **Plasmodium falciparum** and is therefore not used in the treatment of malaria. - While it targets bacterial infections, it lacks the necessary antimalarial activity to clear the parasitic infection. *Quinine* - **Quinine** is an **oral antimalarial drug** that is effective against **P. falciparum**, especially in cases of multidrug resistance. - It works by inhibiting the parasite's ability to detoxify heme, leading to oxidative stress. *Artemether* - **Artemether** is an **artemisinin derivative**, a class of drugs that are highly effective and are the **first-line agents** for treating uncomplicated **P. falciparum malaria**. - It rapidly reduces parasite biomass, particularly in combination with drugs like lumefantrine. *Doxycycline* - **Doxycycline** is a **tetracycline antibiotic** that can be used as an alternative or adjunctive treatment for **P. falciparum malaria**, particularly in areas with resistance to other antimalarials. - It functions by inhibiting protein synthesis in the parasite and is commonly used for both treatment and prophylaxis.

Question 1507: Which antibiotic is known to cause irreversible hearing loss?

A. Gentamicin (Correct Answer)
B. Clarithromycin
C. Vancomycin
D. None of the options

Explanation: ***Gentamicin*** - **Gentamicin** is an **aminoglycoside antibiotic** well-known for its potential to cause **irreversible ototoxicity**, which manifests as permanent hearing loss due to damage to the **cochlear hair cells**. - The risk of ototoxicity is increased with higher doses, prolonged treatment, underlying renal impairment, and concomitant use of other ototoxic drugs. - Aminoglycosides cause concentration-dependent killing and have a narrow therapeutic window, requiring therapeutic drug monitoring. *Clarithromycin* - **Clarithromycin** is a **macrolide antibiotic** that can cause **reversible ototoxicity**, typically manifesting as temporary hearing loss or tinnitus. - Unlike aminoglycosides, the hearing impairment associated with clarithromycin usually resolves upon discontinuation of the drug. - This occurs more commonly with high doses or in patients with renal/hepatic impairment. *Vancomycin* - **Vancomycin** is a **glycopeptide antibiotic** that can cause ototoxicity, particularly when used at high doses or in combination with other ototoxic agents like aminoglycosides. - However, vancomycin-related ototoxicity is **less common and less severe** compared to aminoglycosides, and cases of permanent hearing loss are rare with modern dosing regimens. - The ototoxicity risk is primarily associated with older high-dose formulations. *None of the options* - This option is incorrect because **Gentamicin** is definitively known to cause irreversible hearing loss. - Aminoglycoside ototoxicity is a well-established and clinically significant adverse drug reaction that requires careful monitoring during therapy.

Question 1508: A woman presenting with symptoms of urinary tract infection was prescribed a drug that causes tendon rupture and arthropathy. What is the mechanism of action of the drug?

A. Ribosomal inhibition
B. Cell wall synthesis
C. Inhibition of folic acid synthesis
D. DNA gyrase inhibition (Correct Answer)

Explanation: ***DNA gyrase inhibition*** - The description of a drug causing **tendon rupture** and **arthropathy** in the context of a urinary tract infection (UTI) suggests a **fluoroquinolone**. - Fluoroquinolones exert their bactericidal effect by inhibiting **bacterial DNA gyrase** (also known as topoisomerase II) and **topoisomerase IV**, thereby preventing DNA replication and repair. *Ribosomal inhibition* - This mechanism is characteristic of antibiotics like **aminoglycosides**, **tetracyclines**, and **macrolides**. - While some of these can treat UTIs, they are not typically associated with **tendon rupture** or **arthropathy** as major side effects. *Cell wall synthesis* - This is the mechanism of action for **beta-lactam antibiotics** (e.g., penicillins, cephalosporins) and **vancomycin**. - These drugs are common for UTIs but do not cause **tendon rupture** or **arthropathy**. *Inhibition of folic acid synthesis* - This mechanism is used by **sulfonamides** and **trimethoprim**, often combined as trimethoprim-sulfamethoxazole. - While effective for UTIs, these drugs are not known to cause **tendon rupture** or **arthropathy**.

Question 1509: Which of the following is the drug of choice for preoperative antibiotic prophylaxis in a patient undergoing cardiac surgery?

A. Cefazolin (Correct Answer)
B. Penicillin
C. Clindamycin
D. Vancomycin

Explanation: ***Cefazolin*** - **Cefazolin** is a first-generation cephalosporin that provides excellent coverage against **Staphylococcus aureus** and **Streptococcus species**, which are common pathogens in surgical site infections in cardiac surgery. - It has a favorable safety profile, long half-life allowing for convenient dosing, and good tissue penetration, making it the preferred choice for **preoperative antibiotic prophylaxis** in most cardiac surgery cases. *Penicillin* - **Penicillin** has a narrow spectrum of activity compared to cefazolin and does not adequately cover all potential pathogens in cardiac surgery, particularly **methicillin-susceptible Staphylococcus aureus (MSSA)**. - Due to its limited spectrum, penicillin is generally not recommended for routine **surgical prophylaxis**, especially in complex procedures like cardiac surgery. *Clindamycin* - **Clindamycin** is an alternative for patients with **beta-lactam allergies**, providing coverage against gram-positive organisms and anaerobes. - However, for routine prophylaxis without a specific allergy or high risk of resistant organisms, **clindamycin** is less effective than cefazolin against the most prevalent surgical pathogens. *Vancomycin* - **Vancomycin** is reserved for patients with a known **penicillin allergy** or a high risk of **methicillin-resistant Staphylococcus aureus (MRSA)** colonization or infection. - Its routine use as a primary prophylactic agent in cardiac surgery is discouraged to prevent the development of **vancomycin resistance**.

Question 1510: A 3-week-old infant presents with a cough and sore throat. The mother reports that the infant develops a paroxysm of cough followed by apnea. The total leucocyte count is >50,000 cells/μL. Based on these symptoms, which of the following drugs is the most appropriate treatment for this patient?

A. Azithromycin (Correct Answer)
B. Amoxicillin
C. Cotrimoxazole
D. Erythromycin

Explanation: ***Azithromycin*** - This infant's symptoms are highly suggestive of **pertussis** (whooping cough), characterized by **paroxysmal coughs** followed by **apnea** in young infants, along with **marked leukocytosis**. - **Macrolides** are the treatment of choice due to their effectiveness against *Bordetella pertussis*; **azithromycin** is preferred in infants due to better tolerability and a shorter course compared to erythromycin. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic primarily effective against various bacterial respiratory infections, but it has **no activity against *Bordetella pertussis***. - Using amoxicillin for pertussis would lead to **treatment failure** and a worsening of the infant's condition. *Cotrimoxazole* - While **cotrimoxazole** (trimethoprim-sulfamethoxazole) can be used as an alternative for pertussis in patients **allergic to macrolides**, it is **not the first-line treatment** in infants. - It carries a risk of **kernicterus** in newborns and young infants due to displacement of bilirubin from albumin, so it is generally avoided. *Erythromycin* - **Erythromycin** is a macrolide and is effective against *Bordetella pertussis*, but it is **associated with a higher incidence of infantile hypertrophic pyloric stenosis** when given to young infants. - Due to this adverse effect, **azithromycin** is generally preferred over erythromycin in infants for pertussis treatment.

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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