Absence in amphotericin B‐spiked human plasma of the free monomeric drug, as detected by SERS

Using surface enhanced Raman spectroscopy (SERS) which enables us to specifically detect traces of monomeric amphotericin B (AmB), we were able to show that in a 10(-5) M AmB suspension, the concentration of free drug was below 10(-8) M in the presence of low density lipoproteins (LDL) or plasma. The affinity constant of AmB for LDL determined from electronic absorption data, was found to be 4 x 10(6) M(-1). Therefore, since AmB appears to be in the majority bound to lipoproteins under in vivo conditions, its toxicity should not result from the induction of host-cell transmembrane permeability but rather from the internalization of the AmB-LDL complex.