Background: The withdrawal of digitoxin and subsequent substitution with digoxin around 2012 may have led to an increased health risk for patients. The aim of this study was to follow individual patients during the switch.
Material and method: Serum concentrations of digitoxin and digoxin, measured at the Department of Clinical Pharmacology at St Olavs University Hospital in the period 1 January 2011-31 December 2013 were reviewed. Patients who had switched from digitoxin to digoxin and whose serum concentrations of both drugs had been measured during this period were included.
Results: A total of 304 patients, 1686 samples and 1858 serum concentration analyses were included in the study. Therapeutic serum concentrations were measured in 171 patients (56.3 %) before the switch and 176 (57.9 %) after this had taken place. Altogether 108 patients (35.5 %) had therapeutic concentrations both before and after the change. For 58.9 % of the patients, the change resulted in a reduction in serum concentration of digitalis, calculated as digoxin equivalents. The proportion of patients with assumed supratherapeutic concentrations fell from 43.1 % to 33.9 %; however, the proportion of patients with toxic serum concentrations rose from 0.3 % to 3.0 %.
Interpretation: Although the switch led to a reduction in dose and serum concentration for many, a significant number of patients may have been put in harm's way.