An audit of requests for therapeutic drug monitoring of digoxin: problems and pitfalls.

The use of serum digoxin measurements in a teaching hospital was audited. The reason for test requisition, the timing of blood samples, the recognition of results, and the action taken by house staff were assessed using formal criteria. In 200 consecutive requests for serum digoxin measurements, the reason for requesting the test could not be determined in 165 (82.5%). The timing of plasma samples with respect to duration of therapy and time since last dose was usually satisfactory. However, only 73 (36.5%) of results appear to have been adequately recognized, and approximately 1 result in 4 was followed by an inappropriate decision. High plasma concentrations were usually dealt with more promptly and more appropriately than low plasma concentrations, possibly because the biochemistry laboratory informed physicians directly of the high results. There is a clear need for physicians to better identify the reasons for measuring plasma concentrations of digoxin and to request serum digoxin measurements only when there is a pertinent problem. Indiscriminate requests for serum digoxin measurements are associated with apparent disregard for the results and a high likelihood of making an inappropriate decision regarding further digoxin prescription.