Comparison of serum digoxin level measurement with acetyl strophanthidin tolerance testing.

Serum digoxin levels (SDL) were compared with tolerance for the rapidly acting cardiac aglycone, acetyl strophanthidin (AS). AS titration tests were performed on 133 patients with diverse cardiac disorders. All were receiving maintenance digoxin. Both exquisite AS sensitivity and tolerance for a 1.0 mg AS were associated with a wide range of SDL values. Concordance and discordance between the two methods in assessing degree of digitalization were evaluated by considering SDL of 1.4 ng/ml to be the mean value for patients without glycoside-induced cardiac arrhythmia. An SDL of <1.5 ng/ml with tolerance for 1.0 mg AS and an SDL of >1.4 ng/ml with sensitivity to 1.0 mg AS or less constituted concordant responses. An SDL of <1.5 ng/ml with intolerance for 1.0 mg or less AS and an SDL of >1.4 ng/ml with tolerance for 1.0 mg AS comprised discordant responses. In 60 of 144 (42%) AS titrations discordant results were observed. Severe pulmonic, coronary, and aortic valvular heart disease, as well as old age, contributed to unusual AS sensitivitv. Titration with AS clarified pharmacologic quantification of SDL by providing insight into optimum therapeutic glycoside dose.