The effect of repeated
plasma exchanges on the steady state kinetics of
digoxin (3 patients) and
digitoxin (4 patients) was investigated in 7 patients.
Plasma exchange was performed 3 times a week for 4 weeks up to 12 exchanges using a hollow fiber membrane. In each exchange, 4000 ml plasma were filtered within 1 to 2 h and replaced by an
albumin containing (20 g/l) physiological
electrolyte solution.
Digoxin and
digitoxin concentrations in blood and filtered plasma were measured by radioimmunoassay. The effects due to the amount eliminated by
plasma exchange were distinguished from the effects due to
hypoalbuminemia. The eliminative effect was confined to the plasma compartment. It resulted in a marginal decrease in the elimination half-life from 1.6 to 1.59 days for
digoxin and 4.3 to 4.2 days for
digitoxin. Theoretically, it can be calculated that the
hypoalbuminemia caused an increase in the volume of distribution from 451 to 497 l (
digoxin) and 35 to 50 l (
digitoxin) and a further decrease in the elimination half-life from 4.2 to 4.1 days in the case of
digitoxin (not
digoxin). If given within 2 h prior to
plasma exchange, 13 to 50% of the
digitoxin dose (not
digoxin) was eliminated. Alteration of
digoxin and
digitoxin dosage during repeated
plasma exchanges is not recommended, but drugs should be given after, not before
plasma exchange.