Clinical and Pharmacokinetic Profiles of Digoxin Immune Fab in Four Patients with Renal Impairment

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Abstract
Minimal pharmacokinetic data on digoxin immune Fab are currently available, especially in patients with impaired renal function. The serum concentration-time profiles of total digoxin, free digoxin, and digoxin immune Fab in four patients with moderate to severe renal impairment who received digoxin immune Fab are presented. The calculated elimination half-life of digoxin immune Fab was 25–73 hours. The calculated elimination half-life of total digoxin was 24–72 hours. Free digoxin concentrations rebounded to a peak of 1–2.9 ng/mL 44–97 hours after the administration of digoxin immune Fab. The areas under the curve for digoxin immune Fab were 213–1026 μg·h/mL, and total body clearances were 2.3–7.1 mL/min. The total digoxin concentrations peaked at 14–33 times the pre-Fab digoxin concentrations 5–30 hours after digoxin immune Fab administration. In comparing these data with data available from patients with normal renal function, the half-life of digoxin immune Fab and total digoxin was longer, the peak total digoxin concentration occurred later, the ratio of the peak total digoxin concentration to pre-Fab digoxin concentration was larger, and the rebound in free digoxin occurred later in patients with renal impairment. The Fab dose should not be reduced in patients with renal impairment; however, post-Fab monitoring should be extended to compensate for the prolonged half-life of Fab and later rebound of free digoxin.