Comparison of Plasma Concentrations of Warfarin Measured by Both Simple Extraction and TLC Methods

Abstract

Human volunteers received 25-mg. single oral doses of sodium warfarin. Ninety-three plasma samples were independently assayed by: (a) a simple extraction method, and (b) a TLC method using a UV instead of a fluorescent end-point. Both assays employed 7.5-cm. pathlength cells and the Cary 14 UV spectrophotometer. The assays were concluded to be equivalent and to measure only unchanged warfarin after single doses, since: (a) the least-squares line forced through the origin when assays by the extraction method were plotted against assays by the TLC method had a slope of 1.00; (b) of the differences (TLC — extraction), 44 were positive, 2 were zero, and 47 were negative; and (c) average elimination half-lives of warfarin estimated from terminal plasma concentrations measured by the two methods were not significantly different. The absolute value of the differences averaged 0.17 mcg./ml. with a SD of 0.14 mcg./ml. One may assume that each assay had an average deviation of 0.085 mcg./ml. from the “true” warfarin concentration and that the deviation was independent of the plasma concentration in the range studied (0.1–4.5 mcg./ml.).