EDITOR, - The Antiplatelet Trialists' Collaboration has carried out an important meta-analysis of antiplatelet prophylaxis used to reduce venous thrombosis and pulmonary embolism.1 The results section of the abstract of the paper states: “Information on adding antiplatelet therapy to heparin was limited but, at least for pulmonary embolism, suggested more protection from the combination than from heparin alone.” We suggest that consideration should be given to possible harmful effects of the combination of aspirin and heparin.

The authors found a 62 (SD 33)% reduction in the odds of pulmonary embolism after the combined treatment compared with the same dose of heparin. They also noted a 12 (22)% reduction in the odds of deep vein thrombosis. They do not, however, present any comparisons of total mortality or of complications. We therefore made these comparisons, using data from individual trials given in appendix 1. We found that total mortality was higher with combination treatment than with heparin alone (table). Although this increase was not significant (neither was the reported reduction in pulmonary embolism), it is worrying when considered together with the much higher rate of complications related to bleeding after the combination treatment. In absolute terms the possible benefits of combination treatment could well be …