Experimental impact of assay-dependent differences in plasma indocyanine green concentration determinations

The purposes of the present investigation were (i) to directly compare in man, indocyanine green (ICG) plasma concentrations analyzed by high performance liquid chromatography (HPLC) vs. spectrophotometry; (ii) to evaluate whether the pharmacokinetic parameters generated for ICG from a clinical study are assay-dependent; (iii) to examine whether the method of pharmacokinetic analysis affects the magnitude of any assay-related differences observed in ICG's pharmacokinetic parameters; and (iv) to evaluate whether assay methodology and/or method of pharmacokinetic analysis affect the conclusions derived from a clinical study employing ICG as a marker for hepatic blood flow (HBF). Plasma samples obtained from a clinical study designed to assess the effects of cimetidine and posture on HBF were analyzed by spectrophotometry and HPLC. The spectrophotometric method overestimated ICG plasma concentrations when compared to HPLC. This finding is consistent with the observations of others suggesting the presence of a chemical impurity in the commercial ICG preparation. Data generated by the spectrophotometric method produced lower ICG clearance and HBF estimates and a longer ICG half-life regardless of the method of pharmacokinetic analysis. The method of pharmacokinetic data analysis had no effect on any pharmacokinetic parameter. The experimental conclusions derived from the clinical study were not affected by either analytical methodology or method of data analysis.