Case 4 Digoxin Therapy: Response and Short Half-Life Signalment:  8 year old female hound cross Chief Complaint:  Congestive heart failure due to mitral insufficiency. Pertinent History:  Patient has been receiving digoxin therapy for 8 days. Patient has responded to therapy and is showing no evidence of toxicity. Drug of Interest:  Digoxin Dosing Regimen:  0.008 mg/kg every 12 hours orally. Duration of Current Regimen:  8 days Concern:  Baseline check Other Drugs:  Enalapril, furosemide, phenylbutazone and chlorpheniramine Drug Concentration: 2.88 ng/ml     Time:  1.25 hours 1.42 ng/ml     Time:  9 hours Drug Elimination Half-Life:  7 hours Volume of Distribution:  NA Predicted Peak:  NA Predicted Trough:  NA Recommendation:  Concentrations are above the upper end of the therapeutic range but with no evidence of toxicity, the dose should not necessarily be changed. With a 12 hour half-life, the dosing interval should not be prolonged (and could be reduced to an 8 hour dosing interval with the same total daily dose). Leave dosing regimen as is. Comments:  Compare the drug half-life in this patient to the reported normal (24 hours) and the previous patient. Had a single sample been collected half-way through the dosing interval, concentrations would have been in the lower end of the therapeutic range (see plot) and the dose may have been inappropriately increased. The half-life in this patient indicates that the dosing interval should not be longer than 12 hours. Should a 24 hour dosing interval be used, drug concentrations would approximate 0.35 ng/ml. Follow-Up:  Not available [back to top]