Question

Which drug exerts a fungicidal effect by inhibiting synthesis of the fungal cell wall? (A) micafungin (B) posaconazole (C) flucytosine (D) nystatin (E) terbinafine

Short answer

(A) micafungin

Step-by-step solution

Understand the Question

The question asks for a drug that inhibits the synthesis of the fungal cell wall, resulting in a fungicidal effect. Fungicidal drugs kill fungi, while fungistatic drugs merely inhibit their growth.

Identify Drug Methods of Action

To find the correct answer, we need to know the mechanisms of action of the listed drugs. Micafungin inhibits the synthesis of the fungal cell wall by targeting 1,3-beta-D-glucan synthase, leading to cell death.

Evaluate Other Options

- **Posaconazole** interferes with ergosterol synthesis, affecting the fungal cell membrane. - **Flucytosine** interrupts nucleic acid synthesis within fungal cells. - **Nystatin** binds to ergosterol in the fungal cell membrane, causing pore formation and leakage. - **Terbinafine** inhibits squalene epoxidase, affecting sterol biosynthesis and causing membrane disruption.

Confirm the Correct Answer

Among the options, micafungin directly affects the fungal cell wall by inhibiting glucan synthesis, giving it a fungicidal effect. The others affect different parts of fungal cell physiology and structure, primarily the cell membrane or nucleic acids.

Key concepts

Fungicidal Drugs

Fungicidal drugs are a special group of antifungal agents that work by killing fungal cells. This distinguishes them from fungistatic drugs, which only inhibit fungal growth without killing the fungi. Understanding how each fungicidal drug functions is crucial for effective treatment of fungal infections. Here’s what makes fungicidal drugs unique:

• They target essential processes or components within the fungal cells, leading to cell death.
• They offer a more aggressive approach to controlling fungal infections compared to fungistatic drugs.
• Examples include drugs that interfere with cell wall synthesis, affecting the integrity and survival of the fungus.

By directly acting on critical components like the cell wall, fungicidal drugs like micafungin can effectively eliminate fungal pathogens from the body, making them essential in combating severe fungal infections.

Fungal Cell Wall Synthesis

The fungal cell wall is a vital structure that protects and maintains the shape of the fungal cell. It is also essential for the survival and division of fungal cells. A key component of the fungal cell wall is 1,3-beta-D-glucan, a polymer that provides structural support.
The synthesis of this component is a target for certain antifungal drugs. Here’s how the process works and how it can be disrupted:

• Naturally, 1,3-beta-D-glucan is synthesized by the enzyme 1,3-beta-D-glucan synthase.
• Drugs like micafungin inhibit this enzyme, disrupting the production of glucan.
• This disruption leads to a weakened cell wall, ultimately causing cell lysis and death.

This inhibition is key to the fungicidal effect of micafungin, which makes it effective against a variety of fungal infections, particularly those caused by Candida species.

Mechanisms of Action of Antifungals

Antifungal drugs employ various mechanisms to inhibit or kill fungal cells, depending on their intended target. Understanding these mechanisms helps in selecting the right drug for specific fungal infections. Here are some common mechanisms:

• **Cell Wall Inhibition:** As seen with micafungin, inhibiting glucan synthesis weakens the structural integrity of fungal cells, leading to cell death.
• **Cell Membrane Disruption:** Drugs like nystatin bind to ergosterol in the fungal cell membrane, creating pores and causing vital cellular contents to leak out.
• **Ergosterol Synthesis Interference:** Posaconazole targets ergosterol biosynthesis, an essential component of fungal cell membranes, altering membrane function.
• **Nucleic Acid Synthesis Interruption:** Flucytosine enters fungal cells and inhibits nucleic acid synthesis, preventing cell division and growth.
• **Squalene Epoxidase Inhibition:** Terbinafine acts on sterol biosynthesis by inhibiting squalene epoxidase, which is crucial for maintaining cell membrane structure.

Each antifungal targets different elements of the fungal cell, offering specific advantages depending on the nature and location of the infection. Recognizing these mechanisms can guide effective treatment and management of fungal infections.