Clinical Significance of Serum Digoxin Determination

Abstract

Digoxin is known to have a low margin of safety. Measuring the steady state level of digoxin in serum by radioimmunoassay technique has increased the safety of digoxin therapy, but the current clinical data concerning serum digoxin concentration is still insufficient for utilizing serum digoxin concentration as a reasonable guide for the proper digitalization. This study was aimed to evaluate the digoxin therapy in terms of serum digoxin concentration and to elucidate the pharmacokinetics of digoxin. Results obtained were as follows.
(1) After the oral administration of 0.5mg digoxin in tablet form to normal subjects, the peak serum levels were reached in 45 to 60 minutes and within five hours a relative ly stable plateau was attained.
(2) In 122 patients on chronic digoxin therapy, serum digoxin concentration was 1.17 ± 0.56(S. D. ) ng/ml, ranging from 0.22 to 2.8 ng/ml and daily maintenance dose was 0.25 ± 0.11mg, ranging from 0.125 to 0.5mg. Serum digoxin concentration correlated to maintenanc e dose per day and per kilogram (r= 0.49 and r=0.64, respectively).
(3) “Digoxin Index”, expressed as serum digoxin concentration (ng/ml) divided by daily maintenance dose (mg/kg), was proposed as one of the useful guides for the therapy and the value of 400 or more was considered as being suggestive of potential candidate for intoxication. This index was theoretically related to bioavailability, absorption, volume of distribution and biological half-life of digoxin.
(4) Hemodialysis in patients with chronic renal failure did not significantly influence the serum digoxin level.
(5) The mean digoxin concentration for 8 toxic patients was 3.14 ± 1.41 ng/ml, while the mean level of 122 nontoxic patients was 1.17 ± 0.56 ng/ml (p<0.001). All of the to x ic patients had levels above 2.0ng/ml. Above 2.0ng/ml of serum digoxin concentration and 400 or more of digoxin index carry a high probability of digitalis intoxication.