Antimicrobial Agents — MCQs
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Which of the following antibiotics does not contain a beta-lactam ring?
Rotavirus vaccine is classified as a...?
Pseudojaundice is seen during the treatment with which antituberculous agent?
Lamivudine belongs to which class of antiretroviral drugs?
The combination of trimethoprim and sulfamethoxazole is effective against which of the following opportunistic infections in the AIDS patient?
All of the following are sulphonamides used topically except.
Which of the following drugs is useful in the prophylaxis of meningococcal meningitis?
Second-generation cephalosporin that can be used orally is:
Which of the following antibiotics is the drug of choice for Gram-negative anaerobes?
Which of the following is not an antipseudomonal antibiotic?
Antimicrobial Agents Indian Medical PG Practice Questions and MCQs
Question 1631: Which of the following antibiotics does not contain a beta-lactam ring?
- A. Penicillin
- B. Linezolid (Correct Answer)
- C. Cefotaxime
- D. Imipenem
Explanation: ***Linezolid*** - **Linezolid** is an **oxazolidinone antibiotic**, which has a different chemical structure and mechanism of action compared to beta-lactams. - It works by inhibiting bacterial **protein synthesis** at the ribosomal level, specifically binding to the 23S ribosomal RNA of the 50S subunit. *Penicillin* - **Penicillin** is the prototypic **beta-lactam antibiotic**, characterized by a four-membered beta-lactam ring in its chemical structure [1]. - Its mechanism of action involves inhibiting **bacterial cell wall synthesis** by binding to penicillin-binding proteins (PBPs) [3]. *Cefotaxime* - **Cefotaxime** is a **third-generation cephalosporin**, which belongs to the beta-lactam class of antibiotics [1], [2]. - All cephalosporins, like penicillins, possess a **beta-lactam ring** essential for their antibacterial activity [3]. *Imipenem* - **Imipenem** is a **carbapenem antibiotic**, another class within the beta-lactam family [1]. - Like other beta-lactams, it contains a **beta-lactam ring** and acts by interfering with bacterial **cell wall synthesis** [3].
Question 1632: Rotavirus vaccine is classified as a...?
- A. Live oral (Correct Answer)
- B. Killed intramuscular
- C. Killed subcutaneous
- D. Live subcutaneous
Explanation: **Live oral** - Rotavirus vaccines contain **live-attenuated strains** of the virus, meaning they are weakened but still capable of replicating to induce an immune response. - They are administered **orally**, ensuring exposure to the gastrointestinal tract where the virus naturally infects. *Killed intramuscular* - Killed vaccines contain inactivated pathogens and typically require **intramuscular injection** to stimulate a systemic immune response. - Rotavirus vaccines are not inactivated and are not given via injection. *Killed subcutaneous* - Killed vaccines are inactivated and administered subcutaneously to induce an immune response, but this is not the case for rotavirus vaccines. - The rotavirus vaccine is an **oral, live-attenuated vaccine**, not a killed vaccine. *Live subcutaneous* - While some live vaccines are given subcutaneously (e.g., MMR, varicella), the rotavirus vaccine is explicitly designed for **oral administration**. - Rotavirus vaccine targets the **intestinal immune system** specifically through oral delivery.
Question 1633: Pseudojaundice is seen during the treatment with which antituberculous agent?
- A. Ethambutol
- B. Pyrazinamide
- C. Rifabutin
- D. Rifampicin (Correct Answer)
Explanation: ***Rifampicin*** - **Rifampicin (Rifampin)** causes a benign, harmless **pseudojaundice** characterized by **orange-red discoloration of urine, tears, sweat, saliva, and soft contact lenses**. - This is due to the drug's natural **orange-red pigment** and its excretion in body fluids, NOT due to actual liver dysfunction or bilirubin accumulation. - Patients should be warned about this harmless side effect to avoid unnecessary concern. *Rifabutin* - **Rifabutin**, a rifamycin analog, also causes orange-red discoloration of body fluids similar to rifampicin. - However, **rifampicin is the classic drug** most commonly associated with the term "pseudojaundice" in standard pharmacology references. - Rifabutin is used as an alternative to rifampicin in certain situations (e.g., HIV patients on antiretrovirals). *Ethambutol* - **Ethambutol** is known for causing **optic neuritis (retrobulbar neuritis)**, leading to **red-green color blindness** and visual field defects. - It does not cause jaundice or pseudojaundice. *Pyrazinamide* - **Pyrazinamide** is associated with **hepatotoxicity**, which can manifest as elevated liver enzymes and, in severe cases, actual **jaundice** due to liver damage. - It does not cause pseudojaundice, which is a harmless discoloration without liver dysfunction.
Question 1634: Lamivudine belongs to which class of antiretroviral drugs?
- A. Nucleoside reverse transcriptase inhibitor (Correct Answer)
- B. Nucleotide reverse transcriptase inhibitor
- C. Non-nucleoside reverse transcriptase inhibitor
- D. Protease inhibitor
Explanation: ***Nucleoside reverse transcriptase inhibitor*** - **Lamivudine** is a synthetic nucleoside analog that competitively inhibits **HIV-1 reverse transcriptase**, incorporating into the viral DNA and leading to chain termination [1]. - As a **nucleoside reverse transcriptase inhibitor (NRTI)**, it requires intracellular phosphorylation to its active triphosphate form [1], [2]. *Nucleotide reverse transcriptase inhibitor* - **Nucleotide reverse transcriptase inhibitors (NtRTIs)** are structurally similar to nucleotides, meaning they already contain a phosphate group [2]. - They tend to have a **higher barrier to resistance** and include drugs like **tenofovir disoproxil fumarate** (TDF) and **tenofovir alafenamide** (TAF). *Non-nucleoside reverse transcriptase inhibitor* - **Non-nucleoside reverse transcriptase inhibitors (NNRTIs)** bind directly to a **hydrophobic pocket** on the reverse transcriptase enzyme, causing a conformational change that inhibits its activity [4]. - Unlike NRTIs/NtRTIs, NNRTIs do not require phosphorylation to be active and do not act as **chain terminators** [1]. *Protease inhibitor* - **Protease inhibitors (PIs)** prevent the HIV protease enzyme from cleaving viral polyproteins into functional proteins, which are essential for the assembly of new infectious virions [3], [4]. - This class of drugs, such as **ritonavir** and **atazanavir**, interferes with the final maturation step of the virus [3].
Question 1635: The combination of trimethoprim and sulfamethoxazole is effective against which of the following opportunistic infections in the AIDS patient?
- A. Disseminated Herpes simplex infection
- B. Cryptococcal meningitis infection
- C. Tuberculosis infection
- D. Pneumocystis jirovecii (Correct Answer)
Explanation: ***Pneumocystis jiroveci*** - **Pneumocystis pneumonia (PCP)**, caused by *Pneumocystis jirovecii*, is a common and severe opportunistic infection in AIDS patients. - ** Trimethoprim-sulfamethoxazole (TMP-SMX)**, also known as Bactrim, is the **drug of choice** for both treatment and prophylaxis of PCP [1], [2]. *Disseminated Herpes simplex infection* - **Herpes simplex virus (HSV)** infections are typically treated with antiviral medications like **acyclovir, valacyclovir, or famciclovir**. - TMP-SMX has **no antiviral activity** and is ineffective against HSV. *Cryptococcal meningitis infection* - **Cryptococcal meningitis** is a fungal infection primarily treated with **amphotericin B** in combination with **flucytosine**, followed by fluconazole for maintenance. - TMP-SMX is **not active** against *Cryptococcus neoformans*. *Tuberculosis infection* - **Tuberculosis (TB)**, caused by *Mycobacterium tuberculosis*, requires a **multi-drug regimen** typically including isoniazid, rifampin, pyrazinamide, and ethambutol [3]. - While TMP-SMX has some activity against *Nocardia spp.* and some atypical mycobacteria, it is **not effective** for the treatment of *Mycobacterium tuberculosis*.
Question 1636: All of the following are sulphonamides used topically except.
- A. Silver sulphadiazine
- B. Mafenide
- C. Sulphadiazine (Correct Answer)
- D. Sulphacetamide
Explanation: ***Sulphadiazine*** - **Sulphadiazine** itself is primarily used for **systemic infections** such as toxoplasmosis, often in combination with pyrimethamine. - While it is a **sulfonamide**, it is not formulated for **topical application** in its uncombined form. *Sulphacetamide* - **Sulphacetamide** is commonly used as an **ophthalmic solution** or ointment to treat bacterial **conjunctivitis** and other eye infections. - It is well-suited for **topical application** due to its good tissue penetration and antimicrobial activity against common eye pathogens. *Silver sulphadiazine* - **Silver sulphadiazine** is a widely used **topical cream** for the prevention and treatment of **burn wound infections**. - The combination of **silver ions** and sulphadiazine provides broad-spectrum **antimicrobial activity** against bacteria and fungi in open wounds. *Mafenide* - **Mafenide** is a powerful **topical sulfonamide** primarily used to prevent and treat bacterial **infections in burns**. - It is known for its ability to penetrate **eschar** (necrotic tissue) effectively, making it valuable in deep burn wound management.
Question 1637: Which of the following drugs is useful in the prophylaxis of meningococcal meningitis?
- A. Doxycycline
- B. Minocycline
- C. Cephalexin
- D. Rifampin (Correct Answer)
Explanation: ***Rifampin*** - **Rifampin** is the **first-line agent** for **chemoprophylaxis** of meningococcal meningitis according to CDC guidelines. - Administered as **600 mg twice daily for 2 days** (adults) or **10 mg/kg twice daily for 2 days** (children). - Works by inhibiting bacterial RNA polymerase, achieving excellent penetration into respiratory secretions to eliminate nasopharyngeal carriage of **Neisseria meningitidis**. - Recommended for close contacts of index cases to prevent secondary transmission. *Doxycycline* - **Doxycycline** is **not recommended** for meningococcal prophylaxis in current guidelines. - While it has some activity against Neisseria meningitidis, it is not included in CDC or WHO recommendations due to inconsistent efficacy and the availability of more effective alternatives. - Tetracyclines are not first-line agents for this indication. *Minocycline* - **Minocycline** was historically used for meningococcal prophylaxis but is **no longer recommended**. - Significant side effects including **vertigo, dizziness**, and **ataxia** limit its use. - It has been replaced by safer and more effective alternatives like rifampin and ciprofloxacin. *Cephalexin* - **Cephalexin** is a first-generation cephalosporin used primarily for **skin, soft tissue**, and some **urinary tract infections**. - It is **not effective** against **Neisseria meningitidis** and has **no role** in meningococcal meningitis prophylaxis. - Note: **Ceftriaxone** (third-generation cephalosporin) is an alternative for prophylaxis, but cephalexin is not.
Question 1638: Second-generation cephalosporin that can be used orally is:
- A. Cefepime
- B. Cefalothin
- C. Cefaclor (Correct Answer)
- D. Cefadroxil
Explanation: ***Cefaclor*** - **Cefaclor** is a commonly used **second-generation cephalosporin** that is available in an **oral formulation**, making it suitable for outpatient treatment of various bacterial infections. - Its spectrum of activity includes many Gram-positive and Gram-negative bacteria, often used for **respiratory tract infections** and **otitis media**. *Cefepime* - **Cefepime** is a **fourth-generation cephalosporin**, not a second-generation one, and is primarily administered **intravenously** for severe infections. - It has a broader spectrum against both Gram-positive and Gram-negative bacteria, including **Pseudomonas aeruginosa**. *Cefalothin* - **Cefalothin** (also known as cephalothin) is a **first-generation cephalosporin** that is typically administered **parenterally** (intravenously or intramuscularly). - It is not available in an oral formulation, limiting its use to hospital settings for moderate to severe infections. *Cefadroxil* - **Cefadroxil** is a **first-generation cephalosporin** and is available for oral administration. - While it is an oral cephalosporin, it belongs to the first generation, not the second generation as requested by the question.
Question 1639: Which of the following antibiotics is the drug of choice for Gram-negative anaerobes?
- A. Vancomycin
- B. Aztreonam
- C. Metronidazole (Correct Answer)
- D. Doxycycline
Explanation: ***Metronidazole*** - **Metronidazole** is highly effective against most **Gram-negative anaerobic bacteria**, including *Bacteroides fragilis*, a common pathogen in intra-abdominal infections and abscesses. - It works by forming **nitro-radicals** that damage microbial DNA, exhibiting potent **bactericidal action** against anaerobes. *Aztreonam* - **Aztreonam** is a **monobactam** antibiotic with a narrow spectrum of activity, primarily targeting **Gram-negative aerobic bacteria** (e.g., *Pseudomonas aeruginosa*). - It is **inactive against Gram-positive bacteria** and **anaerobes**, making it unsuitable for Gram-negative anaerobic infections. *Doxycycline* - **Doxycycline** is a **tetracycline antibiotic** with broad-spectrum activity against many Gram-positive and Gram-negative **aerobic** and some anaerobic organisms. - While it has some anaerobic activity, it is **not the drug of choice for significant Gram-negative anaerobic infections** due to resistance patterns and the superior efficacy of metronidazole. *Vancomycin* - **Vancomycin** is primarily used for **Gram-positive bacterial infections**, especially those resistant to other antibiotics like methicillin-resistant *Staphylococcus aureus* (**MRSA**). - It has **no activity against Gram-negative bacteria**, **aerobic or anaerobic**, as its large molecular size prevents penetration of the outer membrane.
Question 1640: Which of the following is not an antipseudomonal antibiotic?
- A. Cephalexin (Correct Answer)
- B. Piperacillin
- C. Ceftazidime
- D. Carbenicillin
Explanation: ***Cephalexin*** - **Cephalexin** is a **first-generation cephalosporin** primarily active against **Gram-positive** bacteria and some Gram-negative organisms, but it lacks activity against *Pseudomonas aeruginosa* [1]. - **First-generation cephalosporins** are generally not effective against **Gram-negative bacteria** resistant to earlier beta-lactams, such as *Pseudomonas*. *Carbenicillin* - **Carbenicillin** is a **carboxypenicillin** that specifically targets **Pseudomonas aeruginosa**, making it an effective antipseudomonal agent. - It was one of the **first penicillin derivatives** developed with substantial activity against *Pseudomonas* and other difficult-to-treat Gram-negative bacteria. *Piperacillin* - **Piperacillin** is a **ureidopenicillin** (extended-spectrum penicillin) known for its robust activity against **Pseudomonas aeruginosa**. - Often combined with a **beta-lactamase inhibitor** like **tazobactam** (as in **piperacillin/tazobactam**) to broaden its spectrum and prevent enzymatic degradation, further enhancing its antipseudomonal efficacy. *Ceftazidime* - **Ceftazidime** is a **third-generation cephalosporin** celebrated for its **excellent activity** against **Pseudomonas aeruginosa** and other Gram-negative bacteria [2]. - Unlike many other third-generation cephalosporins, its primary strength lies in its **antipseudomonal coverage**, making it a key choice for serious *Pseudomonas* infections.
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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