GTC Biotherapeutics (fka GTCB)

[Lewis R Goudy]

"In the treatment of severe sepsis, high-dose antithrombin may sufficiently protect against development of venous thromboembolism when no concomitant heparin is given. Combined administration of the two increases bleeding risk and probably abolishes efficacy of antithrombin."

(cited from same)

http://www.druglib.com/abstract/ho/hoffmann-jn_thromb-haemost_20060500.html

That's about as plain as it gets.