Biodistribution of 4-[(14)C]cholesterol-AmBisome following a single intravenous administration to rats

A biodistribution study of 4-[(14)C]cholesterol-AmBisome; a unilamellar liposomal preparation of amphotericin B was conducted to support a radiolabeled human study. The radioactive plasma concentration profile (as measured in microg-Eq/ml of cholesterol) was best fit to a sum of three exponentials that yielded alpha-, beta-, and gamma-half-life estimates of 3.0 +/- 0.3, 11.8 +/- 3.7, and 113.4 +/- 32.4 h, respectively. Clearance and the steady state volume of distribution were 4.9 +/- 0.2 ml/h/kg and 341 ml/kg. Recovery data collected up through 96 h demonstrated mass balance and indicated that although the elimination profile in both urine and feces were incomplete, the dominant route of elimination (<2% in urine versus 33% in feces) was feces, presumably via biliary excretion of intact liposome and/or cholesterol. The liver, spleen, and lungs, organs of the reticuloendothelial system known for their rapid uptake of liposomes, presented with the highest levels of radioactivity. Levels in the kidney were 15% of that found in the liver and lungs.