Case 3 Digoxin-induced toxicity; long elimination half-life   Signalment:  6 year old male Dachshund cross Chief Complaint:  Congestive heart failure; renal failure Pertinent History:  Patient has been receiving digoxin therapy for 6 months. Within the last 3 months, renal disease has become decompensated. The day prior to presentation, the patient vomited, and became ataxic and disoriented. Patient blood urea nitrogen is 82 mg/dl and creatinine is 1.57 mg/dl. Drug of Interest:  Digoxin Dosing Regimen:  0.005 mg/kg every 12 hours orally. Duration of Current Regimen:  90 days Concern:  Safety Other Drugs:  Enalapril, furosemide, thyroxine Drug Concentration: 2.47 ng/ml     Time:  2 hours 2.40 ng/ml     Time:  12 hours Drug Elimination Half-Life:  > 120 hours Volume of Distribution:  NA Predicted Peak:  NA Predicted Trough:  NA Recommendation:  Concentrations are in the upper end of the therapeutic range and are not necessarily consistent with toxicity. Clinical signs of uremia can not be distinguished from clinical signs of digoxin toxicity. The dose can be decreased by 10 to 25 percent. Comments: The very prolonged half-life for digoxin in this patient presumably reflects decompensated renal disease. The dosing interval can be prolonged to 24 hours in this patient, although the total daily dose should not be decreased more than 10 to 25%. Note that both a peak and a trough sample were helpful in establishing the very prolonged drug elimination half-life and the fact that concentrations do not change during the dosing interval because of the long half-life (see next case). Should the patient respond to therapy and digoxin elimination improve, monitoring is again indicated to establish a new dosing regimen since drug half-life is likely to decrease. Follow-Up:  Not available. [back to top]