Behavior of amphotericin B lipid complex in plasma in vitro and in the circulation of rats

Abstract

Amphotericin B lipid complex (ABLC) shows reduced toxicity relative to that of amphotericin B deoxycholate (AmB-d) while maintaining antifungal activity. Rat blood or plasma was spiked with ABLC in vitro. Released amphotericin B was separated from the parent material by centrifugation. At early times (0 to 15 min) most (approximately 90%) of the amphotericin B was complexed. The amount of released amphotericin B increased gradually in a time- and temperature-dependent fashion. The released amphotericin B was associated with plasma lipoprotein and nonlipoprotein proteins. The area under the concentration-time curve from 0 to 24 h for total amphotericin B in whole blood of rats given a single intravenous bolus dose of 1 mg of ABLC per kg of body weight was fourfold lower than that in rats given 1 mg of AmB-d per kg. The complexed amphotericin B was rapidly removed from the circulation and was distributed to the tissues in these rats. Other rats were treated intravenously with ABLC (10 mg/kg/day) or AmB-d (0.5 mg/kg/day) daily for 15 days. Blood was collected at 15 and 180 min after administration of the last dose. The total levels of amphotericin B in the blood of the group given ABLC were about three to five times those in the group given AmB-d, and the concentration of released, protein-bound amphotericin B in the plasma of the group given ABLC was about one to two times that observed for the group given AmB-d, despite the 20-fold difference in dose. The relative protein distribution of amphotericin B in plasma was similar after ABLC or AmB-d administration under these steady-state conditions in vivo. The rapid uptake of complexed amphotericin B by tissues and the very low levels of circulating protein-bound amphotericin B in plasma after the administration of ABLC may explain, in part, the reduced toxicity and enhanced therapeutic index of this preparation.

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

“…The most striking result of this study is that in the presence of LDL at a concentration higher than 0.02 mg/ml in protein, and 10 −5 M total AmB, after a 15 min incubation, the concentration of free monomeric AmB detected by SERS was very low, significantly lower than 10 −8 M. In blood, the LDL concentration being higher, the amount of bound AmB should also be higher and consequently the free AmB is negligible in these conditions (<10 −8 M). Furthermore, in serum at 25°C, the amount of bound AmB is identical in LDL and HDL (high density lipoprotein) fractions [3], higher in VLDL and in non‐lipoprotein fractions [4]. Under these conditions, it can be said that at the concentration of total AmB found in the sera of Fungizone‐treated patients, that is around 5×10 −6 M, the amount of free monomeric AmB in the blood is negligible.…”

“…The formation of these pores has been widely ascertained in serum‐free media or in red blood cells, which are devoid of low density lipoprotein (LDL) receptors. However, AmB binds to serum proteins, in particular to LDL [2–4], which may affect its mechanism of action. Therefore, the following questions arise: whether the affinity of AmB for proteins is higher than that for cells and whether it is the AmB‐protein complex which is active, or whether there is an exchange of the antibiotic between proteins and membrane; and whether the complex AmB‐LDL is internalized by the LDL receptors of mammalian cells.…”

“…Unfortunately, in vivo, HPLC or bioassays, currently used to determine the total AmB concentration in plasma, do not provide this essential information. One study has, however, shown that in the blood of rats treated with AmB, 80% of the amphotericin B is bound to plasma proteins [4]. In vitro, several studies have also shown that AmB binds to lipoproteins.…”

“…In vitro, several studies have also shown that AmB binds to lipoproteins. The distribution of the drug among the different lipoproteins was also analyzed in detail [2–4]. Unfortunately, the procedure used did not allow a clear estimation of free AmB, the amount of which, above or below ca.…”

Amphotericin B lipid preparations: what are the differences?

“…In‐vitro studies with ABLC suggested that host tissue‐derived phospholipases played a role in releasing AMB from ABLC [26], but in another study, incubating ABLC with plasma resulted in greater than 50% of the AMB being released directly into the plasma. The majority of the released drug was not associated with plasma lipoproteins [27]. Further studies are needed to elucidate the factors involved in release of the AMB from the phospholipid complex.…”