*Binds to cell membranes which contain sterols, such as ergosterol, cholesterol

*Ergosterol is the predominant sterol in many of the fungal membranes.

*Amphotericin has an affinity for the ergosterol membranes.

*Amphotericin interferes with the function of ergosterol as a stiffening agent in the fungal membranes; all sterols inhibit lysis for plasma membranes.

*It then forms a channel through the membrane.

*Amphotericin increases the permeability of the cell membrane.

* Small molecules,  such as potassium and glucose can then leak through.

*The leaking results in lysis  and cell death.
 

Drug Structure and its Relationship with Activity and Potency
 

Rules for effective Activity and Potency:

1.)  The drug structure must include an amine and carboxylate.  This provides a structure that directly resembles a cell membrane ( a phospholipid).
2.)  The drug structure must include a triple hydroxyl group.  This very non-polar region serves as a flat receptor site.
3.)  The drug structure must have a polar and non-polar end so that it resembles a phospholipid which has both a polar head and a non-polar body.

Distinguishing Between Activity and Potency of Amphotericin B

Amphotericin B is very active.  Amphotericin B’s potency can vary though.  At low concentrations the drug is fungistatic.  At high concentrations the drug can be fungicidal.  Since Amphotericin is so active,  small quantities of the drug are necessary to be therapeutic as a fungistatic agent.  A normal dosage would be around 750 mg of Amphotericin B.