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It is highly likely that you have an unreliable result just 24hrs after the administration of Digibind. I'm not sure what the clearance rate is with normal renal function, but in subjects with significantly reduced renal function I have seen digibind still present in sufficient quantity to interfere up to 2 weeks later. One problem of course is that Digibind is designed to be extremely avid for digoxin so even very low circulating levels will cause problems, and it is very difficult to identify the interference or when it has cleared. If you can find someone with a method with a different antibody strategy (e.g. simple immunoassay vs sandwich) you may be able to follow the disappearance from sequential samples. The simple single antibody assay should start with apparently very high digoxin levels (all the labelled dig will be bound to the digibind so mimicing very high in vivo digoxin) whereas the sandwich assay will give apparently very low digoxin levels ( no free digoxin to complete the sandwich). As the digibind disappears the two results should converge.
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You can overcome the problem by doing a free/bound separation. There is a very convenient device called Centrisart untrafiltration device. You just out a small plasma/serum specimen into the central tube and spin it for a few minutes. Central tube has a membrane with MW cut-off (various). You then test the ultrafiltrate. Adds about 10 minutes to the normal test.
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The following link
takes you to the FDA page for Digibind. Half-life with normal renal
function is around 15-20 hours so, using the normal rule of 5 half-lives I guess
you’ll need to wait around 4 days before it has been eliminated, probably longer
in renal impairment. In your patient, 24hrs after Digibind, it is likely
that apparent serum levels will be much higher than free digoxin as Digibind
will “pull” digoxin from tissue leading to high digoxin levels, but not
dangerous as the majority of the digoxin should be bound to the immunoglobulin
fragment. (But you can read all of this in the FDA page! ;-)) http://www.drugs.com/pro/digibind.html