Antimicrobial Agents Practice Questions

Q: Which strain is used in the Mumps vaccine?

Jeryl Lynn. **Jeryl Lynn** - The **Jeryl Lynn strain** is a live attenuated mumps virus strain commonly used in the development of the **mumps vaccine**, particularly in the **MMR vaccine**. - This strain was developed in the 1960s and has a proven track record of safety and efficacy in preventing mumps infection. *Oka* - The **Oka strain** is primarily associated with the **live attenuated varicella (chickenpox) vaccine**. - It is not used in the mumps vaccine, which targets a different viral pathogen. *Danish 1331* - Danish 1331 is a strain associated with a particular **Mycobacterium bovis Bacillus Calmette-Guérin (BCG)** vaccine for **tuberculosis**, not mumps. - BCG vaccines are used to prevent tuberculosis and are distinct from viral vaccines. *Edmonston Zagreb* - The **Edmonston-Zagreb strain** is a live attenuated measles vaccine strain, commonly used in some regions for the **measles, mumps, and rubella (MMR) vaccine**. - While it is part of the MMR vaccine, it specifically targets measles, not mumps.

Q: 'Savlon' contains:

Cetavlon and hibitane. ***Cetavlon and hibitane*** - Savlon is a well-known **antiseptic formulation** that contains both **cetrimide** (often marketed as Cetavlon) and **chlorhexidine gluconate** (referred to as hibitane) [1]. - **Cetrimide** is a quaternary ammonium compound acting as a **surfactant** and antiseptic [2], while **chlorhexidine** is a broad-spectrum antiseptic [1]. *Hibitane and chloroxylenol* - While **hibitane (chlorhexidine)** is a component of Savlon [1], **chloroxylenol** is not. - **Chloroxylenol** is the active ingredient in Dettol, another common antiseptic. *Cetavlon and chloroxylenol* - **Cetavlon (cetrimide)** is part of Savlon's formulation [2], but **chloroxylenol** is not. - These two active ingredients originate from different popular antiseptic products. *Chlorhexidine and chloroxylenol* - **Chlorhexidine** is a component of Savlon [1], but **chloroxylenol** is not. - This option incorrectly substitutes part of the Dettol formulation for a component of Savlon.

Q: All of the following drugs cause renal failure except?

Cefoperazone. ***Cefoperazone*** - **Cefoperazone** is a third-generation cephalosporin that is primarily eliminated by the liver and does not typically cause **nephrotoxicity**. - While all cephalosporins can potentially cause hypersensitivity reactions or interstitial nephritis in rare cases, cefoperazone is not known for direct renal tubular damage. *Amphotericin B* - **Amphotericin B** is a potent antifungal agent that frequently causes dose-dependent **nephrotoxicity** due to direct damage to renal tubular cells. - It can lead to acute kidney injury, electrolyte imbalances (e.g., **hypokalemia**, **hypomagnesemia**), and renal tubular acidosis. *Gentamicin* - **Gentamicin** is an aminoglycoside antibiotic known for its significant **nephrotoxic** potential, particularly with prolonged use or high doses. - It accumulates in renal cortical cells, leading to **proximal tubular necrosis** and acute tubular necrosis. *Cephaloridine* - **Cephaloridine** is a first-generation cephalosporin that was historically removed from the market due to its significant and dose-dependent **nephrotoxicity**. - It caused direct damage to the **renal tubules**, leading to acute kidney injury.

Q: Which of the following drugs are used topically for dermatophytes?

All of the options. ***All of the options*** - **Terbinafine**, **Ciclopirox olamine**, and **Econazole** are all commonly used as topical antifungal agents for the treatment of dermatophyte infections. - These drugs target different aspects of fungal cell metabolism or structure to inhibit growth or kill the fungus. *Terbinafine* - It is an **allylamine antifungal** that inhibits **squalene epoxidase**, an enzyme involved in fungal ergosterol synthesis. - While effective topically, terbinafine can also be used orally for more extensive or recalcitrant infections, but the question specifically asks for topical use. *Cyclopirox olamine* - This is a **hydroxypyridone antifungal** that acts by chelating polyvalent metal cations, inhibiting essential enzymes in fungal cells. - It is often used for topical treatment of dermatophyte infections, including **tinea pedis** and **tinea corporis**, and is also used for onychomycosis. *Econazole* - It is an **imidazole antifungal** that inhibits the fungal cytochrome P450 enzyme 14α-demethylase, which is crucial for **ergosterol biosynthesis**. - Commonly available as a cream or solution, econazole is effective against a broad spectrum of fungi, including dermatophytes, and is used for various superficial fungal infections.

Q: Mechanism of action of terbinafine?

Inhibition of ergosterol synthesis. ***Inhibition of ergosterol synthesis*** - Terbinafine specifically inhibits **squalene epoxidase**, an enzyme involved in the **biosynthesis of ergosterol**, a crucial component of fungal cell membranes. - This inhibition leads to the accumulation of **squalene**, which is toxic to the fungal cell, and a deficiency of ergosterol, compromising membrane integrity and fungal growth. *Inhibition of microtubule formation* - This mechanism is characteristic of **griseofulvin**, another antifungal agent, which interferes with fungal mitosis by disrupting the assembly of microtubules. - Terbinafine does not target microtubule formation; its action is focused on the fungal cell membrane pathway. *Prevents formation of purine* - This mechanism is associated with drugs like **flucytosine**, which is converted into an active metabolite that interferes with fungal DNA and RNA synthesis by inhibiting purine and pyrimidine synthesis. - Terbinafine's fungicidal action is unrelated to purine metabolism. *Binds to ergosterol* - This mechanism describes **polyene antifungals** such as **amphotericin B** and **nystatin**, which directly bind to ergosterol in the fungal cell membrane, creating pores and leading to leakage of cellular contents. - Terbinafine does not directly bind to ergosterol but rather prevents its synthesis.

Q: The drug of choice in mycoplasma pneumonia in children is –

Erythromycin. ***Erythromycin*** - **Erythromycin**, a macrolide antibiotic, is the drug of choice for treating **Mycoplasma pneumoniae** infections in children. - **Mycoplasma pneumoniae** lacks a cell wall, making antibiotics that target cell wall synthesis (like penicillins or cephalosporins) ineffective. Macrolides inhibit protein synthesis. *Tetracycline* - **Tetracyclines** are effective against **Mycoplasma pneumoniae**, but are generally avoided in children under 8 years due to the risk of permanent **tooth discoloration** and **bone growth inhibition**. - While effective, its side effect profile in pediatric patients makes it a less preferred first-line option. *Cotrimoxazole* - **Cotrimoxazole** (trimethoprim/sulfamethoxazole) is effective against various bacterial infections but is not the primary drug of choice for **Mycoplasma pneumoniae**. - Its mechanism of action involves inhibiting folate synthesis, which is not the principal target for **Mycoplasma** infections. *Streptomycin* - **Streptomycin** is an aminoglycoside antibiotic primarily used for treating **tuberculosis** and some severe gram-negative infections. - It is not effective against **Mycoplasma pneumoniae** and has significant side effects, including **ototoxicity** and **nephrotoxicity**.

Q: Which one of the following antibiotics inhibits transpeptidation in bacterial cell wall synthesis?

Penicillin. ***Penicillin*** - Penicillin is a **beta-lactam antibiotic** that targets bacterial cell wall synthesis by inhibiting the enzyme **transpeptidase** (penicillin-binding proteins). - This inhibition prevents the cross-linking of **peptidoglycan strands**, leading to a weakened cell wall and subsequent bacterial lysis. *Chloramphenicol* - **Chloramphenicol** inhibits bacterial protein synthesis by binding to the **50S ribosomal subunit**, thereby preventing peptide bond formation (peptidyl transferase activity). - It does not act on the bacterial cell wall. *Vancomycin* - **Vancomycin** is a **glycopeptide antibiotic** that inhibits bacterial cell wall synthesis by binding to the **D-Ala-D-Ala terminus** of peptidoglycan precursors. - It prevents the **transglycosylation and transpeptidation steps** by blocking substrate access, but it does not directly inhibit the transpeptidase enzyme itself like beta-lactams do. - Its mechanism is distinct from penicillin's direct enzyme inhibition. *Amphotericin* - **Amphotericin B** is an **antifungal agent** that targets the fungal cell membrane by binding to **ergosterol**, forming pores that disrupt membrane integrity. - It has no activity against bacterial cell wall synthesis.

Q: Continued suppression of bacterial growth after antibiotic levels have fallen below the Minimum Inhibitory Concentration (MIC) is known as?

Post antibiotic effect. ***Post antibiotic effect*** - The **post-antibiotic effect (PAE)** refers to the continued suppression of bacterial growth after antibiotic levels have fallen below the **Minimum Inhibitory Concentration (MIC)**. - This phenomenon allows for less frequent dosing while maintaining efficacy, which is important for drug scheduling. *Time dependent killing* - **Time-dependent killing** means that the duration for which the antibiotic concentration stays above the **MIC** is the most important factor for efficacy, not necessarily the peak concentration. - Antibiotics with this characteristic, such as **beta-lactams**, often require frequent dosing or continuous infusion. *Sequential blockade* - **Sequential blockade** occurs when two drugs act on consecutive steps in a metabolic pathway, leading to a synergistic effect that results in enhanced microbial killing. - A classic example is the combination of **sulfamethoxazole and trimethoprim**, which inhibit different enzymes in the folic acid synthesis pathway. *Concentration dependent killing* - **Concentration-dependent killing** indicates that the rate and extent of bacterial killing increase as the antibiotic concentration rises, particularly when it exceeds the **MIC**. - Antibiotics like **aminoglycosides** exhibit this effect, often benefiting from high peak concentrations to maximize efficacy.

Q: Which of the following statements about terbinafine is FALSE?

Its activity is restricted to dermatophytes. Its activity is restricted to dermatophytes - This statement is **false** because while **terbinafine** is highly effective against **dermatophytes**, it also exhibits activity against other fungi like *Candida* species and *Aspergillus*, especially at higher concentrations. - Its broad-spectrum fungicidal action differentiates it from azoles, which are primarily fungistatic and target a wider range of fungi. *It is effective in onychomycosis* - **Terbinafine** is a **first-line treatment** for **onychomycosis** due to its high efficacy, ability to penetrate nail tissue, and fungicidal action against dermatophytes [1]. - It accumulates in the nail plate, providing sustained antifungal effects, leading to high cure rates in fungal nail infections. *It is unlikely to produce anti-androgenic side effects* - **Terbinafine** acts by inhibiting **squalene epoxidase** in the fungal cell membrane, which is distinct from the **cytochrome P450 enzymes** involved in **steroid hormone synthesis**. - Therefore, it does not interfere with human androgen receptors or steroid synthesis pathways, making **anti-androgenic side effects** highly unlikely, unlike some azole antifungals. *It is not effective in cryptococcal meningitis* - **Terbinafine** primarily concentrates in **skin, nails, and adipose tissue**, and its **penetration into the central nervous system (CNS)** is poor. - **Cryptococcal meningitis** requires antifungal agents that can effectively cross the blood-brain barrier, such as **amphotericin B** and **flucytosine**, which terbinafine cannot achieve [1].

Question 1

Which strain is used in the Mumps vaccine?

Accepted Answer

Jeryl Lynn

Answer

Oka

Answer

Danish 1331

Answer

Edmonston Zagreb

Question 2

'Savlon' contains:

Accepted Answer

Cetavlon and hibitane

Answer

Hibitane and chloroxylenol

Answer

Cetavlon and chloroxylenol

Answer

Chlorhexidine and chloroxylenol

Question 3

All of the following drugs cause renal failure except?

Accepted Answer

Cefoperazone

Answer

Amphotericin B

Answer

Gentamicin

Answer

Cephaloridine

Question 4

Which of the following drugs are used topically for dermatophytes?

Accepted Answer

All of the options

Answer

Terbinafine

Answer

Cyclopirox olamine

Answer

Econazole

Question 5

Mechanism of action of terbinafine?

Accepted Answer

Inhibition of ergosterol synthesis

Answer

Inhibition of microtubule formation

Answer

Prevents formation of purine

Answer

Binds to ergosterol

Question 6

Paucibacillary leprosy treatment includes

Accepted Answer

Rifampicin 600 mg once a month for 6 months + Dapsone 100 mg daily for 6 months

Answer

Rifampicin 600 mg daily + Dapsone 100 mg daily for 6 months

Answer

Rifampicin 600 mg + Dapsone 100 mg + Clofazimine for 12 months

Answer

Dapsone 100 mg daily + Clofazimine 300 mg daily for 6 months

Question 7

The drug of choice in mycoplasma pneumonia in children is –

Accepted Answer

Erythromycin

Answer

Tetracycline

Answer

Cotrimoxazole

Answer

Streptomycin

Question 8

Which one of the following antibiotics inhibits transpeptidation in bacterial cell wall synthesis?

Accepted Answer

Penicillin

Answer

Chloramphenicol

Answer

Amphotericin

Answer

Vancomycin

Question 9

Continued suppression of bacterial growth after antibiotic levels have fallen below the Minimum Inhibitory Concentration (MIC) is known as?

Accepted Answer

Post antibiotic effect

Answer

Time dependent killing

Answer

Sequential blockade

Answer

Concentration dependent killing

Question 10

Which of the following statements about terbinafine is FALSE?

Accepted Answer

Its activity is restricted to dermatophytes

Answer

It is effective in onychomycosis

Answer

It is unlikely to produce anti-androgenic side effects

Answer

It is not effective in cryptococcal meningitis

Antimicrobial Agents — MCQs

Antimicrobial Agents — MCQs

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