Influence of Low Molecular Weight Heparin on the Hemostatic System After Abdominal Surgery

The use of low molecular weight heparins for postsurgical deep vein thrombosis prevention in orthopaedic patients

The prophylactic antithrombotic efficacy of a low molecular weight heparin was compared with a traditional unfractionated calcium heparin after orthopaedic surgery in 140 patients. Deep vein thromboses were detected in legs either by Doppler sonography or [125I]fibrinogen uptake tests in five (7.1%) and seven (10%) patients, respectively. The capacity of both drugs to prevent deep vein thrombosis was demonstrated. Compared with the control group, those who used low molecular weight heparin showed a significant increase of activated factor X inhibition and smaller increases in activated partial thromboplastin times. Tolerability of both drugs was good, with a low incidence of local side-effects.

Absorption of heparin, LMW heparin and SP54 after subcutaneous injection, assessed by competitive binding assay

Unfractionated heparin, pentosan polysulphate (SP54) and the low molecular weight heparins CY216 and CY222 were injected subcutaneously at a minimum of weekly intervals into 5 healthy volunteers. The dose was 75 mg in all cases. Concentrations of administered glycosaminoglycan in serial plasma samples and voidings of urine were measured using a competitive binding assay, and biological activity was assessed in plasma using APTT and anti-Xa clotting assays. There was wide individual variation in the absorption of unfractionated heparin as indicated both by the maximal plasma concentrations reached 2-3 h after injection and by the area under the concentration vs. time curve. The efficiency of absorption increased and the individual variation decreased with decreasing molecular weight of the administered glycosaminoglycan. Urinary excretion correlated with plasma concentration, and recovery in the urine also increased with decreasing molecular weight. Similar patterns of uptake and clearance were indicated by the APTT and competitive binding assays, but anti-Xa clotting activity could be detected in the plasma after clearance of the administered glycosaminoglycan.