21.   Such drugs have been needed to prevent formation of blood clots that block the artery at the site of the cleared obstruction.

22.   The clot apparently formed because the amount of anticoagulation drugs that he was taking to prevent formation of such clots was too low, his doctors said.

23.   The condition improved about eight hours after injection of an enzyme, urokinase, and an anticoagulant, heparin, to prevent formation of additional clots.

24.   The drug is already approved to prevent the formation of clots after angioplasty.

25.   The researchers hoped that the treatment would prevent the formation of polyps in the first place.

26.   The selenium sponge helped prevent the formation of scar tissue in the rabbits, whose eyes are more prone to scarring than humans.

27.   The radiation works to slow the growth of the smooth muscle cells in the arteries, preventing the formation of scar tissue.

28.   There, he received an injection of Lovenox to help prevent formation of new blood clots.

29.   This method prevents the formation of air pockets that can cause the top crust to fall.

30.   Poland will take efforts to prevent formation of long lines at the border, Lis said.