ABC of monitoring drug therapy. Digoxin.

The plasma digoxin concentration that will result from a given dose of the drug can be predicted at best with only 34% accuracy, although knowledge of a previous concentration improves the ability to predict subsequent concentrations. In outpatients taking a fixed daily dosage, a steady state plasma digoxin concentrations vary widely (between 0 5 and 3 5 nmol/l). This means that if a target plasma digoxin concentration is desirable measuring the concentration may be useful in tailoring dosages to individual requirements. In this article we apply to digoxin the criteria (described in the previous article on measuring plasma drug concentrations) which must be fulfilled in part or in full before the measurement of its plasma concentration can be considered worth while.