Digoxin therapeutic drug monitoring: age influence and adverse events

Digoxin is a cardiac glycoside, used to control rapid ventricular rates in atrial fibrillation and to reduce the hospitalizations due to heart failure. Digoxin has a narrow therapeutic range. So, in the treatment of older patients (≥ 65 years), it is important to set the optimal dose of digoxin to prevent toxicity and therapeutic drug monitoring of digoxin trough plasmatic concentration (C0) may be useful.

To assess measured C0, to evaluate age influence on digoxin pharmacokinetic parameters and to report adverse events in patients administered digoxin.

It consisted in a retrospective study. We included all the patients addressed to the department of clinical pharmacology for digoxin C0 measurement by an automated fluorescence polarization immunoassay. Therapeutic ranges of digoxin C0 were: 1 to 2.5 ng.mL-1 in children, 0.8 to 2 ng.mL-1 in adults and 0.5 to 0.9 ng.mL-1 in older adults (≥ 65 years) in atrial fibrillation and heart failure.

We collected 183 samples from 132 patients. Sex ratio M/W was 0.47. Mean age was 60 years and 57% of patients were older adults. Mean dose of digoxin was 0.3 mg.day-1. In older adults, 45% were administered daily doses over 0.125 mg.day-1. Mean digoxin C0 was 1.6 ng.mL-1. There was more supra-therapeutic C0 in older adults than younger ones (p<0.0001).There was no correlation between C0 and daily dose of digoxin. Adverse events, mainly cardiac and digestive, were reported in 47 patients (36%), among this population 47% were older adults.

TDM is useful to prevent toxicity, mainly in older adults where diagnosis may be difficult to establish.