The serum digoxin concentration: ten questions to ask.

Although the role of digoxin therapy has been the subject of debate, the drug is generally accepted as effective in the treatment of heart failure due to systolic dysfunction and as therapy for atrial fibrillation and supraventricular tachyarrhythmias. Serum digoxin concentrations are commonly used to gauge patient response to digoxin. Digoxin pharmacokinetics are complex, and many factors can confound the interpretation of digoxin concentrations. The exact therapeutic range of serum digoxin varies in the literature but should be considered to be from 0.8 to 2.0 ng per mL, on the basis of population data regarding therapeutic response and toxicity. Renal function plays a major role in digoxin pharmacokinetics and is an important factor in determining digoxin doses. Many medications, including quinidine, amiodarone and verapamil, alter digoxin pharmacokinetics and can result in two- to three-fold increases in the serum digoxin concentration. Effective interpretation of the digoxin concentration requires consideration of the patient's renal function and clinical status, possible drug interactions, time of the assay and other variables.