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An antifungal drug is medication used to treat fungal infections such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as cryptococcal meningitis, and others. Such drugs are usually obtained by a doctor's prescription or purchased over-the-counter.
Additional recommended knowledge
List of antifungal drugs
Antifungals work by exploiting differences between mammalian and fungal cells to kill off the fungal organism without dangerous effects on the host. Unlike bacteria, both fungi and humans are eukaryotes. Thus fungal and human cells are similar at the molecular level. This means it is more difficult to find a target for an antifungal drug to attack that does not also exist in the infected organism. Consequently, there are often side-effects to some of these drugs. Some of these side-effects can be life-threatening if not used properly.
There are several classes of antifungal drugs.
A polyene is a circular molecule consisting of a hydrophobic and hydrophilic region. This makes polyene an amphoteric molecule. The polyene antimycotics bind with sterols in the fungal cell membrane, principally ergosterol. This changes the transition temperature (Tg) of the cell membrane, thereby placing the membrane in a less fluid, more crystalline state. As a result, the cell's contents leak out (usually the hydrophilic contents) and the cell dies. Animal cells contain cholesterol instead of ergosterol and so they are much less susceptible. (Note: as polyene's hydrophobic chain is reduced, its sterol binding activity is increased. Therefore, increased reduction of the hydrophobic chain may result in it binding to cholesterol, making it toxic to animals.)
Imidazole and triazole antifungals
The imidazole and triazole antifungal drugs inhibit the enzyme cytochrome P450 14α-demethylase. This enzyme converts lanosterol to ergosterol, and is required in fungal cell membrane synthesis. These drugs also block steroid synthesis in humans.
The triazoles are newer, and are less toxic and more effective:
Allylamines inhibit the enzyme squalene epoxidase, another enzyme required for ergosterol synthesis:
Echinocandins inhibit the synthesis of glucan in the cell wall, probably via the enzyme 1,3-β glucan synthase:
Antifungal drugs are often found in dandruff shampoos. Among the most common are pyrithione zinc,selenium sulphide and ketoconazole (Nizoral).
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Antifungal_drug". A list of authors is available in Wikipedia.|