Appropriateness of the use of serum digoxin and digitoxin assays

The use of 145 digoxin and digitoxin assays was studied in a teaching hospital to determine if performance of assays was appropriate and therapeutically beneficial. Patient charts (121) were randomly selected from a list of all patients for whom digoxin or digitoxin assays were performed. Charts were compared with established criteria to determine whether the assay was indicated and performed correctly and whether dosage was adjusted correctly based on assay results. Of the assays reviewed, 49% were performed for irrational indications; 86% were performed appropriately under steady-state conditions; and 96% used serum samples appropriately drawn more than six hours after administration of the last digitalis glycoside dose. Of the assays performed at appropriate times in relation to dose and at steady-state plasma concentrations (120), 31 should have and 89 should not have resulted in a dosage change. Of the latter, 98% were evaluated correctly. Of the former, 36% were not evaluated correctly (i.e., indicated dosage adjustments were not made). Control of the use of digitalis glycoside assays is needed. Pharmacists should become involved in monitoring drug assays to assure appropriateness of assay request, interpretation and follow-up.