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Aspirin, a 110-year-old molecule, is a cornerstone in the treatment of atherothrombotic patients. The concept of aspirin "resistance" emerged approximately 15 years ago and is of growing interest. Aspirin resistance, defined as a lack of inhibition of cyclo-oxygenase-1 (COX-1), is a rare phenomenon and its clinical relevance can hardly be studied. On the contrary, residual platelet hyperactivity is more common and affects 20 to 30% of aspirin-treated patients. This latter phenomenon corresponds to sustained platelet reactivity despite a proper inhibition of COX-1 by aspirin. Several meta-analyses suggest that residual platelet hyperactivity could be a risk factor for the recurrence of ischemic events in aspirin-treated patients. Causes of biological non-responsiveness to aspirin are discussed, including the role of compliance, drug-drug interactions, genetic polymorphisms and diabetes mellitus. Ongoing studies are designed to find out the mechanisms of residual platelet hyperactivity, determine its potential clinical relevance and delineate the more appropriate assays in order to identify patients who may benefit of a tailored antiplatelet therapy.

Aspirin, a 110-year-old molecule, is a cornerstone in the treatment of atherothrombotic patients. The concept of aspirin "resistance" emerged approximately 15 years ago and is of growing interest. Aspirin resistance, defined as a lack of inhibition of cyclo-oxygenase-1 (COX-1), is a rare phenomenon and its clinical relevance can hardly be studied. On the contrary, residual platelet hyperactivity is more common and affects 20 to 30% of aspirin-treated patients. This latter phenomenon corresponds to sustained platelet reactivity despite a proper inhibition of COX-1 by aspirin. Several meta-analyses suggest that residual platelet hyperactivity could be a risk factor for the recurrence of ischemic events in aspirin-treated patients. Causes of biological non-responsiveness to aspirin are discussed, including the role of compliance, drug-drug interactions, genetic polymorphisms and diabetes mellitus. Ongoing studies are designed to find out the mechanisms of residual platelet hyperactivity, determine its potential clinical relevance and delineate the more appropriate assays in order to identify patients who may benefit of a tailored antiplatelet therapy.

A 19-year old male patient with hereditary antithrombin III type I deficiency was admitted for thrombosis of the right iliac, femoral and popliteal veins. Treatment with a low molecular weight heparin resulted in recanalization of the veins confirmed by phlebography. After two weeks of treatment, the drug was replaced by another low molecular weight heparin and this was followed, 3 weeks later, by a documented relapse of thrombosis.

This open, randomised multicenter trial compares the efficacy and safety of Fragmin administered subcutaneously twice daily with standard heparin administered by continuous infusion in the treatment of deep vein thrombosis (DVT). The initial dose of Fragmin is 100 U anti-Xa/kg/12 h and the further doses are adjusted according to the anti-Xa activity between 0.5 and 0.8 U/ml, 3 hours after the morning injection. The initial dose of standard heparin is 240 UI/kg/12 h. The dose adjustments are based on the daily results of APTT (1.5 - 3 times the control). Treatments efficacy are appreciated when comparing the venography performed before and after 10 days of treatment. The safety is evaluated on clinical parameters and iterative biological tests. Sixty-six patients have been included in this study. Efficacy of the two treatments is equivalent with a phlebographic improvement in respectively 79.3 p. 100 (Heparin Group) and 71.0 p. 100 (Fragmin Group) of the cases and an aggravation in 3.4 p. 100 and 6.4 p. 100 (NS) respectively. The frequency of dosage adjustments is lower and the stability of biological tests is better in the Fragmin group. In conclusion, the administration of Fragmin twice daily by subcutaneous route seems to be equivalent at least to standard heparin continuous infusion in the treatment of recent DVT. The better convenience and safety of Fragmin have to be verified on a larger panel of patients.