A routine method for the determination of digoxin in urine by radioimmunoassay

We describe a radioimmunoassay for the routine determination of digoxin in urine employing readily available commercial reagents. The standard curve was found to exhibit very good linearity represented by a composite correlation coefficient of 0.9993 and a standard error of estimate which was less than 1% of the digoxin concentration range of interest. Between-assay precision was excellent as reflected by the coefficient of variation (CV) which averaged 5.29%. Studies assessing the recovery of the present method showed satisfactory results of 106% at a low level of digoxin excretion and 102% at a higher excretion level. Our laboratory carried out a study of digoxin bioavailability in which a standard digoxin dose of 500 micrograms was given to 16 volunteers and the present radioimmunoassay method was employed to measure digoxin excretion. An amount equal to 33.4 +/- 6% of the drug given was eliminated 48 h following digoxin dosing.