Protein precipitation: An expedient procedure for the routine analysis of the plasma metabolites of [I-123]IBZM

Plasma metabolite analysis of the single photon emission computed tomograph y (SPECT) D-2/D-3 receptor radiotracer (S)(-)-N-[(1-ethyl-2-pyrrolidinyl)me thyl] 2-hydroxy-3-[I-123]iodo-6-methoxy-benzamide ([I-123]IBZM) is needed f or the equilibrium analysis of the SPECT data, in brain imaging studies inv olving bolus plus constant infusion paradigm. The purpose of these experime nts was to find an appropriate procedure to expedite this analysis during r outine determinations. The procedure was applied to the plasma analysis of 22 human subjects. Each plasma sample was subjected to acetonitrile protein precipitation. After separation of the pellet, the acetonitrile fraction c ontained 91% +/- 2% (n = 88) of the mixture of labeled metabolites and pare nt compound. The recovery coefficient of unmetabolized [I-123]IBZM determin ed with an standard plasma sample was 95% +/- 2% (n = 22). The percent pare nt compound present in the extracted fraction, measured by high performance liquid chromatography, was 16% +/- 9% (n = 85) and the percent metabolites was 84% +/- 9% (n = 85), Free fraction determination (f(1), fraction of ra diotracer unbound to protein), was 4% +/- 0.8% (n = 22). Free fraction of p arent was 15% +/- 8% (n = 85). The results indicate that acetonitrile prote in precipitation is an adequate method for the analysis of the [I-123]IBZM plasma metabolites. NUCL MED BIOL 26;7:811-814, 1999. (C) 1999 Elsevier Sci ence Inc. All rights reserved.