Final answer:
Antifungal drugs work primarily by disrupting ergosterol biosynthesis, which is essential for fungal cell membrane integrity. Azoles and allylamines are two common classes of antifungals that target ergosterol. Other antifungals interfere with chitin in the cell wall or microtubules during cell division.
Step-by-step explanation:
Modes of Action of Antifungal Drugs
The primary mode of action for antifungal drugs involves targeting the fungal cell membrane or cell wall. Specifically, these drugs often disrupt the biosynthesis of ergosterol, a critical component of fungal cell membranes. Ergosterol maintains membrane fluidity and function for fungi, whereas human cells contain cholesterol. Drugs that inhibit ergosterol synthesis are thus selectively toxic to fungi while sparing human cells. One of the most common classes of such antifungal medications is the azole group, including drugs like miconazole. Another group is the morpholines, which also interfere with the synthesis of membrane sterols.
Some antifungals target the cell wall by interfering with the production of chitin, which is a component unique to the fungal cell wall. Despite the effectiveness of antifungal drugs in treating infections, they often have more toxic side effects compared to antibacterial drugs because eukaryotic fungi are more similar to human cells than prokaryotic bacteria are.
Allylamines such as terbinafine inhibit an earlier step in ergosterol biosynthesis and are often used topically but can also be taken orally for severe infections, though hepatotoxicity can be a concern with oral administration. The antifungal griseofulvin acts by disrupting microtubule formation during mitosis, which can also result in hepatotoxicity and, therefore, is reserved for specific types of infections.