Digoxin Elimination in a Functionally Anephric Patient After Digoxin-Specific Fab Fragment Therapy

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Abstract
The elimination of total digoxin after digoxin-specific Fab fragment therapy in a patient in end-stage renal disease is described. Two-component, nonlinear exponential regression of the patient''s total digoxin concentration data revealed biphasic elimination: a fast phase with a half-life of 43 h and a slow phase with a half-life of 330 h. Serum total digoxin concentration decreased 20% 12 h after the initiation of Fab fragment therapy. The mean serum concentrations of total digoxin and apparent total digoxin as measured by fluorescence polarization immunoassay during a 520-h period after the initiation of therapy were 18.42 and 14.77 ng/ml, respectively (n = 15). The correlation between the two measurements was good (r = 0.987). The time course of free digoxin concentration obtained after ultrafiltration at 2, 20, or 37.degree. C is also described. The free digoxin concentrations (n = 10) at these temperatures averaged over a 282-h period were 0.35, 0.53, and 0.82 ng/ml, respectively (p < 0.001, 2.degree. C vs. 37.degree. C).