Evaluation of digoxin pharmacokinetics in a patient undergoing continuous venovenous hemofiltration

Purpose: This case report highlights the use of digoxin for right ventricular (RV) support in a critically ill patient requiring continuous venovenous hemofiltration (CVVH) after left-ventricular assist device placement.  Therapeutic drug monitoring was utilized in order to 1) calculate the sieving coefficient (sc) of digoxin and 2) estimate appropriate dosing of digoxin based on extracorporeal unit clearance.

Methods: Pre-filter serum, post-filter serum, and dialysate digoxin concentrations were drawn to calculate the sc.  Samples were drawn six to eight hours after digoxin administration and were collected within five minutes of each other. Sampling of serum and dialysate concentrations were conducted in duplicate on consecutive days in order to verify the accuracy of serum and dialysate concentrations. 

Results: The sc was calculated [(2 x dialysate concentration) / (pre-filter concentration + post-filter concentration)] as 0.80 and 0.76.  Extracorporeal unit clearance was estimated to be ~28 mL/min based on an ultrafiltration rate of 2.2L/hr [calculated by the ultrafiltration rate (mL/min) x sieving coefficient]. Therapeutic serum levels were achieved after calculation and dosing strategy implementation. 

Conclusions: Digoxin appears to be cleared by CVVH with a sc of ~0.8. This information could be used to design a dosing regimen that may prevent drug accumulation in patients who require CVVH.  Current labeling of digoxin recommends dose reductions of 25-75% or an increase in dosing interval for this calculated extracorporeal unit clearance.  The patient was placed on digoxin 125mcg every other day (50% dose reduction) which achieved therapeutic levels for RV support. Further studies are needed to evaluate and verify the pharmacokinetics of digoxin in critically ill patients undergoing CVVH.