What is the mechanism of action for Ketoconazole?

• A. Inhibits protein synthesis
• B. Alters cell wall permeability
• C. Blocks ergosterol synthesis
• D. Interferes with DNA replication

Answer: (C)

Ketoconazole works primarily by blocking ergosterol synthesis, which is a crucial component of fungal cell membranes. Ergosterol is similar to cholesterol in human cells but is specific to fungi. When ketoconazole inhibits the enzyme lanosterol 14α-demethylase, part of the ergosterol biosynthetic pathway, it leads to a disruption in cell membrane formation. This disruption can cause increased membrane permeability and ultimately result in cell death, as the integrity of the fungal cell membrane is compromised.

Other options provided relate to different mechanisms of action for various drugs. For instance, inhibiting protein synthesis is typically associated with antibiotics like tetracyclines or aminoglycosides, while altering cell wall permeability is relevant to antifungal medications like polyenes. Interfering with DNA replication is a mechanism seen in certain classes of antiviral agents and chemotherapeutics, not with antifungals like ketoconazole. Therefore, the action of ketoconazole is specifically tied to its ability to block ergosterol synthesis, making it an effective treatment against fungal infections.