Antimicrobial Agents — MCQs

Antimicrobial Agents Indian Medical PG Practice Questions and MCQs

Question 1371: Persistent suppression of microbial growth below MIC is known as:

A. Paradoxical effect
B. Post antibiotic effect (Correct Answer)
C. Adverse effect
D. Post exposure prophylaxis

Explanation: ***Post antibiotic effect*** - This phenomenon refers to the continued **suppression of bacterial growth** even after the antibiotic concentration has fallen below the **minimum inhibitory concentration (MIC)**. - It allows for less frequent dosing intervals without compromising efficacy. - Clinically important for **aminoglycosides and fluoroquinolones**, which exhibit significant PAE. *Paradoxical effect* - The **paradoxical effect** (or Eagle effect) refers to the phenomenon where certain antibiotics, particularly penicillin, become *less effective* at very high concentrations. - This effect is not about persistent suppression below MIC, but rather a **decreased bactericidal activity** at concentrations far exceeding MIC. *Post exposure prophylaxis* - **Post exposure prophylaxis (PEP)** refers to preventive treatment given after exposure to an infectious agent (e.g., HIV PEP, rabies PEP). - This is a clinical intervention strategy, not a pharmacodynamic phenomenon describing antibiotic behavior below MIC. *Adverse effect* - An **adverse effect** refers to an unintended and undesirable reaction to a drug, which is not relevant to the described microbial growth suppression. - This term describes harmful side effects experienced by the patient, not a microbiological phenomenon.

Question 1372: Drugs of choice for MRSA in skin and soft tissue infections are:

A. Clindamycin, Vancomycin
B. Vancomycin, Linezolid (Correct Answer)
C. Vancomycin, Teicoplanin
D. Dicloxacillin, Vancomycin

Explanation: ***Vancomycin, Linezolid*** - **Vancomycin** is a cornerstone for treating **MRSA** infections, particularly severe ones, due to its efficacy against resistant staphylococci. - **Linezolid** is an alternative for **MRSA** infections, especially in cases of vancomycin resistance or intolerance, and offers good oral bioavailability. *Clindamycin, Vancomycin* - While **vancomycin** is correct, **clindamycin** has varying efficacy against **MRSA** and high rates of inducible resistance, making it less reliable as a primary drug of choice. - Clindamycin's use for MRSA often requires initial susceptibility testing, including a **D-test**, to rule out inducible clindamycin resistance. *Vancomycin, Teicoplanin* - **Vancomycin** is a primary **MRSA** drug, but **teicoplanin** is largely used in Europe and is structurally similar to vancomycin, often reserved for cases where vancomycin is not tolerated or preferred. - While effective, **teicoplanin** is not as universally recognized as a first-line option alongside vancomycin in all regions. *Dicloxacillin, Vancomycin* - **Vancomycin** is appropriate, but **dicloxacillin** is an **anti-staphylococcal penicillin** and is not effective against **MRSA** (Methicillin-Resistant Staphylococcus aureus) because MRSA, by definition, is resistant to all beta-lactam antibiotics. - Dicloxacillin is mainly used for **MSSA** (Methicillin-Sensitive Staphylococcus aureus) infections.

Question 1373: Not true about iodophores?

A. Surfactants
B. Inorganic compounds (Correct Answer)
C. Release iodine
D. Disinfectant

Explanation: ***Inorganic compounds*** ✓ **Correct Answer** - This statement is **NOT TRUE** - Iodophores are **organic complexes**, not inorganic compounds. - They are formed by combining iodine with a **solubilizing agent** or carrier molecule, typically a surfactant or polymer (e.g., povidone-iodine). - This organic formulation allows for **controlled release** of iodine and reduces irritation compared to free iodine solutions. *Surfactants* - Many iodophores are formulated with **surfactants** to enhance their solubility and wettability. - These surfactants help to release the **active iodine** gradually, providing sustained antimicrobial action. *Release iodine* - Iodophores function by **slowly releasing free iodine**, which is the active antimicrobial agent. - This gradual release mechanism provides a **prolonged antiseptic effect** while minimizing irritation. *Disinfectant* - Iodophores are widely used as **disinfectants** and antiseptics in healthcare settings and for skin preparation. - Their broad-spectrum antimicrobial activity makes them effective against **bacteria, viruses, fungi, and spores**.

Question 1374: Treatment of Neurocysticercosis includes all of the following except -

A. Praziquantel
B. Niclosamide (Correct Answer)
C. Albendazole
D. Corticosteroids

Explanation: ***Niclosamide***- **Niclosamide** is an oral anthelmintic primarily used to treat **intestinal tapeworm infections** by inhibiting **oxidative phosphorylation** in the parasites.- It has **poor systemic absorption** and therefore is **not effective** against **neurocysticercosis**, which involves cysts in the brain parenchyma requiring drugs with good CNS penetration.*Praziquantel*- **Praziquantel** is an orally administered anthelmintic that increases the **calcium permeability** of the parasite's cell membrane, leading to paralysis and death.- It is used in the treatment of **neurocysticercosis**, particularly for **viable parenchymal cysts** and as an alternative to albendazole [2].*Albendazole*- **Albendazole** is a broad-spectrum anthelmintic that works by inhibiting **tubulin polymerization**, causing disruption of **parasite metabolism** and glucose uptake.- It is considered the **first-line treatment** for **parenchymal neurocysticercosis** due to its excellent penetration into the central nervous system and proven efficacy.*Corticosteroids*- **Corticosteroids** (such as **dexamethasone** or **prednisolone**) are used as **adjunct therapy** in neurocysticercosis management.- They help reduce **inflammation and edema** associated with parasite death, preventing complications like seizures and increased intracranial pressure during anthelmintic treatment [1].

Question 1375: Penicillin should be given to a patient with group A beta haemolytic streptococci infection of the tonsils for a period of:

A. 21 days
B. 3-5 days
C. 1 month
D. 10-14 days (Correct Answer)

Explanation: ***10-14 days*** - A **10-day course** of oral penicillin is the standard recommendation for treating **Group A beta-hemolytic streptococcal (GABHS) pharyngitis** to ensure complete eradication of the organism. - This duration helps prevent complications like **acute rheumatic fever** and **acute post-streptococcal glomerulonephritis**. - Some guidelines extend treatment up to 14 days to ensure compliance and complete bacterial eradication. *21 days* - A 21-day antibiotic course is generally **too long** for uncomplicated GABHS pharyngitis and can increase the risk of antibiotic resistance or side effects. - This duration might be considered for more severe or recurrent infections, but not as an initial standard treatment. *3-5 days* - A 3-5 day course of antibiotics is **insufficient** for eradicating GABHS and significantly increases the risk of developing future complications like **rheumatic fever**. - While some antibiotics for other conditions have shorter courses, penicillin for strep throat requires a longer duration to be effective. *1 month* - A 1-month course of penicillin is **excessively long** for uncomplicated GABHS pharyngitis and is not indicated for this condition. - Such prolonged antibiotic therapy is typically reserved for ongoing prophylaxis in patients with a history of **rheumatic fever** or specific deep-seated infections.

Question 1376: Which is not used in acne?

A. Doxycycline
B. Ampicillin (Correct Answer)
C. Clindamycin
D. Erythromycin

Explanation: ***Ampicillin*** - **Ampicillin** is a penicillin-class antibiotic primarily used for bacterial infections like respiratory tract infections, urinary tract infections, and meningitis; it has no significant role in the treatment of acne. - Its spectrum of activity and mechanism do not target the specific processes involved in **acne pathophysiology**, such as reducing *Propionibacterium acnes (P. acnes)* growth or inflammation relevant to acne. *Doxycycline* - **Doxycycline** is a tetracycline antibiotic commonly used in acne treatment due to its anti-inflammatory properties and its ability to inhibit the growth of *P. acnes*. - It reduces sebum production and targets inflammatory lesions, making it effective for **moderate to severe inflammatory acne**. *Clindamycin* - **Clindamycin** is a lincosamide antibiotic often used topically for acne due to its effectiveness against *P. acnes* and its anti-inflammatory effects. - It helps reduce bacterial load on the skin and diminish the inflammatory response associated with acne lesions. *Erythromycin* - **Erythromycin** is a macrolide antibiotic that can be used topically or orally for acne due to its ability to kill *P. acnes* and its anti-inflammatory properties. - It is an alternative for patients who cannot tolerate tetracyclines or for whom other treatments are not effective, though **bacterial resistance** has limited its use.

Question 1377: What is the drug that can be used for rheumatic fever prophylaxis in a patient with a history of allergy to Penicillin?

A. Erythromycin (Correct Answer)
B. Amoxicillin
C. Streptomycin
D. Sulfasalazine

Explanation: ***Erythromycin*** - **Erythromycin** is a macrolide antibiotic that is a suitable alternative for **rheumatic fever prophylaxis** in patients with a documented allergy to penicillin. - It effectively covers *Streptococcus pyogenes*, the causative agent of group A streptococcal (GAS) pharyngitis that precedes rheumatic fever. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic and would be contraindicated in a patient with a **penicillin allergy**, as it carries a high risk of cross-reactivity and allergic reaction. - Using amoxicillin in this scenario could lead to severe hypersensitivity reactions, compromising patient safety. *Streptomycin* - **Streptomycin** is an aminoglycoside antibiotic primarily used for infections like **tuberculosis** and severe bacterial endocarditis. - It is not indicated for the treatment of *Streptococcus pyogenes* infections or for **rheumatic fever prophylaxis**. *Sulfasalazine* - **Sulfasalazine** is an anti-inflammatory and immunomodulatory drug primarily used in the management of **inflammatory bowel disease** and **rheumatoid arthritis**. - It has no antimicrobial activity against *Streptococcus pyogenes* and is therefore not used for **rheumatic fever prophylaxis**.

Question 1378: Red man syndrome is caused by

A. Vancomycin (Correct Answer)
B. Ciprofloxacin
C. Teicoplanin
D. Amikacin

Explanation: ***Vancomycin*** - **Red man syndrome** is a well-known adverse reaction associated with **rapid intravenous infusion** of vancomycin. - It results from the **non-IgE mediated release of histamine** from mast cells and basophils. *Ciprofloxacin* - This antibiotic belongs to the **fluoroquinolone** class and is primarily associated with side effects such as **tendon rupture**, **QT prolongation**, and **GI disturbances**, not red man syndrome. - Ciprofloxacin has a different mechanism of action and adverse effect profile compared to vancomycin. *Teicoplanin* - While **teicoplanin** is a glycopeptide antibiotic similar to vancomycin, it is much **less likely** to cause red man syndrome due to its different molecular structure and slower histamine-releasing potential. - It generally has a more favorable safety profile regarding infusion-related reactions. *Amikacin* - **Amikacin** is an **aminoglycoside** antibiotic known for side effects like **ototoxicity** and **nephrotoxicity**. - It does not cause red man syndrome, as its mechanism of action and adverse effects are distinctly different from vancomycin.

Question 1379: A patient was given chloroquine and doxycycline for 7 days. The patient's fever decreased in 4 days, but on day 6, parasitemia recurred with reappearance of asexual forms of Plasmodium falciparum on peripheral smear. This type of drug resistance is?

A. R1 type (Correct Answer)
B. R3 type
C. R4 type
D. R2 type

Explanation: ***R1 type*** - **R1 resistance (Resistance level I)** is characterized by **initial clearance or marked reduction of asexual parasitemia followed by recrudescence within 7 days** of treatment initiation. - In this case, the fever decreased (indicating initial parasite suppression), but asexual forms reappeared on day 6, fulfilling the criteria for R1 resistance. - This represents **partial drug sensitivity** where parasites are initially suppressed but not completely eliminated. *R2 type* - **R2 resistance (Resistance level II)** involves **marked reduction but not complete clearance** of asexual parasitemia during treatment. - Parasites remain detectable throughout treatment without an initial period of clearance. - This patient showed initial improvement with subsequent recrudescence, which is characteristic of R1, not R2. *R3 type* - **R3 resistance (Resistance level III)** signifies **complete failure of treatment with no reduction** in asexual parasite count. - This patient's fever decreased in 4 days, indicating at least partial response, ruling out R3 resistance. *R4 type* - **R4 is not a recognized category** in the WHO classification of antimalarial drug resistance. - The standard WHO classification includes only **R1, R2, and R3 resistance levels** based on asexual parasite response to treatment.

Question 1380: Which of the following regimens is recommended for multibacillary leprosy in children of 10 to 14 years of age?

A. Rifampicin 600 mg once a month (under supervision) + Dapsone 50 mg daily (self-administered)
B. Rifampicin 600 mg once a month (under supervision)+ Dapsone 100 mg daily (self-administered)+ Clofazimine 50 mg once a month (under supervision) and 25 mg every alternate day
C. Rifampicin 450 mg once a month (under supervision) + Dapsone 50 mg daily (self-administered)
D. Rifampicin 450 mg once a month (under supervision)+ Dapsone 50 mg daily (self-administered)+ Clofazimine 150 mg once a month (under supervision) and 50 mg every alternate day (Correct Answer)

Explanation: ***Rifampicin 450 mg once a month (under supervision)+ Dapsone 50 mg daily (self-administered)+ Clofazimine 150 mg once a month (under supervision) and 50 mg every alternate day*** - This regimen reflects the **reduced dosages** for children aged 10-14 years for all three drugs: Rifampicin, Dapsone, and Clofazimine, as recommended by WHO guidelines for multibacillary leprosy. - The combination of these three drugs is crucial for effective treatment of **multibacillary leprosy**, which involves multiple lesions and higher bacterial load, for a duration of 12 months. *Rifampicin 600 mg once a month (under supervision) + Dapsone 50 mg daily (self-administered)* - While Dapsone dosage is appropriate, the **Rifampicin dosage (600 mg)** is too high for a child of this age group. - This regimen also omits **Clofazimine**, which is an essential drug for multibacillary leprosy treatment to prevent drug resistance and reduce bacterial load. *Rifampicin 600 mg once a month (under supervision)+ Dapsone 100 mg daily (self-administered)+ Clofazimine 50 mg once a month (under supervision) and 25 mg every alternate day* - The dosages for **Rifampicin (600 mg)** and **Dapsone (100 mg)** are both adult dosages and are too high for children aged 10-14 years. - The Clofazimine dosage also differs from the recommended pediatric dosage for multibacillary leprosy. *Rifampicin 450 mg once a month (under supervision) + Dapsone 50 mg daily (self-administered)* - While the Rifampicin and Dapsone doses are appropriate for children, this regimen is missing **Clofazimine**, making it incomplete for the treatment of multibacillary leprosy. - Omission of Clofazimine would lead to a higher risk of **treatment failure** and drug resistance in multibacillary cases.

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

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free