[Dosing of digitoxin in clinical practice].

In 2007, new Norwegian guidelines suggested that serum concentrations of digitoxin should be in the interval 8 - 15 nmol/l, which is about 50 % lower than previous recommendations. We studied trends in dosing and serum concentrations of digitoxin in the period 2000 - 08, based on 13 054 serum samples sent to our laboratory for analysis in that period. The median serum concentration of digitoxin was stable until the end of 2006 (at about 25 nmol/l); then it gradually decreased from 2007 until the end of 2008 (to 19 nmol/l). The mean daily dose decreased from 66 microg to 56 microg in the study period. At a given dose, patients above 85 years of age had serum concentrations that were almost twice as high as those for patients younger than 55 years. This age effect was particularly pronounced from 65 years. Serum concentrations of digitoxin have gradually decreased after 2007, but are often higher than the new reference range. To obtain serum concentrations within the new reference interval, doses at least as low as those currently recommended should be used, particularly in the oldest patients.