Do broad spectrum antibiotics cause nosebleeds?

When an individual takes such an antibiotic, it kills a large number of bacteria normally found in the intestine. Because these bacteria produce vitamin K, their elimination substantially decreases the amount of vitamin K that is available to the liver for the production of prothrombin, a procoagulant that is vital to clotting reactions. With decreased amounts of prothrombin in the blood , normal daily injuries such as breaks in the vessels in the nasal passageways, which are normally sealed off quickly by coagulation, do not seal off as quickly, producing the effect of noseblees.