Safety of high doses of low molecular weight heparin (Fragmin) in acute myocardial infarction. A dose-finding study.

We postulated that low molecular weight heparin (LMWH) in doses producing plasma levels in the range of 0.6-1.0 anti-Xa U/ml may reduce the incidence of left ventricular thrombi (LVT) secondary to acute anterior wall myocardial infarction (AAMI). In an open, dose-finding study, 72 patients with acute myocardial infarction (AMI) were treated with Fragmin (KABI) 240-360 anti-Xa U/kg/24h subcutaneously for 6-10 days. 300 anti-Xa U/kg/24h given as 2 or 3 injections resulted in a mean plasma concentration of about 0.8 anti-a U/ml. There were 3 minor haemorrhages, all in a subgroup of 22 patients also being treated with 0.3 g aspirin orally per day after 1.5 mill. U streptokinase intravenously on admission. In the 38 patients with AAMI receiving 300 anti-Xa U/kg/24h there were only 3 LVT during the period of treatment (8%). In conclusion, 300 anti-Xa U Fragmin/kg/24h s.c to patients with AMI appears safe, but minor haemorrhage may occur in patients receiving aspirin concomitantly. Although these data are limited, the low incidence of LVT in patients with AAMI suggests efficacy of this dose of Fragmin to prevent LVT.