Monday January 16, 2006
LMWH and Antidot (protamine)
If protamine is given within 4 hours of the enoxaparin (Low Molecular Weight Heparins - LMWH), then a neutralizing dose is: 1 mg of protamine per 1 mg of enoxaparin. The IV protamine should be administered slowly atleast over 10 minutes as rapid infusion may cause anaphylactoid type reaction. May repeat half of earlier dose of protamine after 6 hours with postulation that half life of enoxaparin is longer than protamine.
It appears that that the LMWH anti-Xa reversal is not related to protamine-LMWH binding or LMWH size, but rather to the density of sulfate residues in the particular LMWH. Another available variety of LMWH, dalteparin (Fragmin) has higher degree of sulfonation and appear to be more responsive to protamine reversal.
2 clinical pearls
1. Protamine does not help in reversing bleeding from Fondaparinux (Arixtra). Only supportive treatment should be given with mean half-life of fondaparinux of 17-21 hours in mind.
2. Fresh frozen plasma is ineffective in reversal of LMWH to achieve hemostasis and should not be use in these situations.
References: Click to get article/abstract
1. Accidental overdosage following administration of Lovenox - rxlist.com
2. Incomplete Reversal of Enoxaparin Toxicity by Protamine: Implications of Renal Insufficiency, Obesity, and Low Molecular Weight Heparin Sulfate Content - Obesity Surgery, Volume 14, Number 5, 1 May 2004, pp. 695-698(4)
