Lepirudin has a short half-life, and only 50-60% of the intravenously admin
istered dose is excreted by the kidneys. The fate of the remainder is unkno
wn, We designed a study to determine the fate of this lepirudin. In each of
six baboons, [I-131]lepirudin was given intravenously as a bolus or infuse
d over 30 min, 24 h apart. The in vivo redistribution of [I-131]lepirudin w
as determined and quantified by scintillation camera imaging, In all studie
s, the half-life of [I-131]lepirudin, as determined from the disappearance
of radioactivity, was 21 +/- 3 min. The half-life determined from the disap
pearance of lepirudin, measured by the Ecarin Clotting Time (ECT) method, w
as similar at 23 +/- 8 min. Results obtained with the labeled lepirudin are
therefore comparable with those obtained using the plasma concentration of
lepirudin. When lepirudin was administered as a bolus, the half-life was 1
8 +/- 4 min, and lepirudin was cleared from the plasma at a rate of 42 +/-
12 mL/min and by the kidneys at 23 +/- 2 mL/min. Following infusion over 30
min, the half-life and total and renal clearances were not significantly d
ifferent. In both studies, between 50 and 60% of the administered lepirudin
was excreted by the kidney. Studies on sacrificed baboons showed that appr
eciable amounts of lepirudin were present in the bile, indicating the liver
as a contributor to the elimination of lepirudin.