Outpatients with acute SVT of at least 4 cm in length of the internal or external saphenous veins or their collaterals were randomized in a double blind fashion to receive either parnaparin 8500 UI aXa od for ten days followed by placebo for 20 days or 8500 UI aXa od for ten days followed by 6400 UI aXa od for 20 days or 4250 UI aXa od for 30 days .