Not all drugs should be prescribed generically, as indicated by Drs Carter and Tarshis. Digoxin is one that is best prescribed by brand name. As pointed out in our article, the Food and Drug Administration itself did not approve digoxin for substitution under the New York State generic prescribing law.I think that there is enough "bobbling" room in the current digoxin bioavailability standards to raise the question of clinical difficulties when patients' therapies are switched from one generic manufacturer's formulation to another. As Drs Carter and Tarshis point out, one could measure the serum digoxin concentration each time a question arises. However, at Strong Memorial Hospital, this test costs $20. The patient could purchase an 18-month supply of Lanoxin in our pharmacy for the same amount of money. Additionally, this analysis assumes that the serum digoxin concentration will nearly always be helpful in caring for the patient.