Matsuzaki et al. reported 87 % of the total radioactivity administered was recovered in urine (24 h). This apparent difference can be explained in light of the fact that Matsuzaki
et al. used FA labeled at the acyl carbon. Previous studies have shown that this acyl carbon Fosbretabulin is retained in FA metabolites , so it is not surprising that 87 % of the radioactivity was excreted in the earlier study since much of this radioactivity would be associated with metabolites. Umezawa has also shown that <5 % FA is excreted unchanged in the urine . Linear pharmacokinetics were not observed for the IV doses administered in this study. Non-linear pharmacokinetic parameters suggest that metabolic enzymes, transporters, and protein-FA interactions are saturated at the concentrations produced within the dose range of 10–75 mg/kg. These are the first and only studies of this type conducted in any species. Earlier reports on the acute toxicity observed mild gastrointestinal hemorrhage Salubrinal and erosion in Wistar male rats following administration of 32 mg/kg FA by gavage . This dose is very close to the 25 mg/kg dose administered in the present study
and therefore some of the same gastrointestinal effects might be DNA Synthesis inhibitor expected here as well. Since necropsies were not performed in the current study, the degree of intestinal damage was not assessed. The bioavailability of FA (58 %), while not optimal, demonstrates that further pharmacokinetic and toxicity studies in larger animals such as dogs and non-human primates are warranted. The effects of dose on the IV pharmacokinetic parameters raise some questions on the ability to safely scale the dosage from rat to human use. Repeating these studies in higher order animal species, such as non-human primates, should in part answer questions Epothilone B (EPO906, Patupilone) of dose scalability of FA use in humans. Conflict of interest None. Open AccessThis article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution,
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