Serum glycoside concentrations were measured by rubidium 86 assay in 88 patients on maintenance digitalis therapy not manifesting digitalis toxicity and in 39 patients manifesting digitalis toxicity by cardiac arrhythmias. The nontoxic range and median in nanograms per milliliter were 0 to 5 (1.2) for digoxin, 0 to 38 (20.5) for digitoxin, and 2 to 40 (23) for digitalis leaf. Toxic levels (digoxin, 2 to 44 [5.5]; digitoxin, 15 to 56 ; digitalis leaf, 31 to 64 ) were significantly higher (P <.001)—half above upper nontoxic limits and 37 higher than the nontoxic medians. Serial measurements demonstrated prolonged glycoside excretion rates in all eight patients with toxic reactions to digoxin (half-life, 2.9 to 10 days) and in eight of 13 patients with toxic reactions to digitoxin or digitalis leaf (half-life, 4.9 to 9.9 days). Serum glycoside concentrations and excretion rates are useful in managing patients with suspected digitalis toxic reactions.
Ritzmann LW, Bangs CC, Coiner D, Custis JM, Walsh JR. Serum Glycoside Levels by Rubidium Assay. Arch Intern Med. 1973;132(6):823–830. doi:10.1001/archinte.1973.03650120031006