Serum digoxin concentrations in a representative digoxin-consuming adult population.

As part of health examination of a representative sample of an adult population (n = 8000) serum digoxin concentration was measured in 661 patients on continuous digoxin therapy. The prescribed mean daily dose of digoxin was significantly higher in men (223 micrograms) than in women (201 micrograms); the dose significantly decreased with increasing age. The mean serum digoxin concentration was the same in men and women and it differed insignificantly between age groups, although older persons tended to have a higher concentration. The age - adjusted mean steady state digoxin concentration was 1.02 ng/ml in men and 0.98 ng/ml in women; in about 60% the concentration was within the "therapeutic" range (0.80-2.00 ng/ml). The concentrations were clearly related to daily dose of digoxin. At equal dose levels old persons tended to have higher concentrations than younger persons. The interindividual variation in serum digoxin concentrations was very wide. However, when digoxin measurements in the same subjects were repeated about three months later, a good correlation between the two measurements was found. The interval between the last dose of digoxin and the collection of blood (up to 41 h) had relatively little effect on individual serum digoxin concentrations. Patients on concomitant thiazide or loop diuretic therapy had the same mean serum digoxin concentration as those not-receiving a diuretic. The mean concentration was significantly higher in patients taking a thiazide or loop diuretic combined with triamterene. The difference may have been due to an interaction between triamterene and digoxin.