In vivo neutralization of low-molecular weight heparin fraction CY 216 by protamine

The neutralization in vivo of a low molecular weight heparin by protamine was investigated. Large doses and excessive doses of intravenously administered CY 216 were studied. An intravenous injection of protamine given 10 minutes after the administration of CY 216 did not cause the studied biologic parameters to return to normal levels, but merely attenuated them, whatever the protamine dosage tested. In contrast, the bleeding time and the volume of blood loss resumed normal values that were close to those observed in the controls. This dissociation of actions cannot be explained at present. The ratio of protamine to CY 216 dosage that produced the best results was 1 antiheparin U of protamine to 2 anti-Xa U of CY 216. Nevertheless CY 216 appeared to have a small hemorrhagic potential.