Provision of study drug: There is no oral form of vitamin K currently marketed in Canada, thus our previous investigations have used the intravenous formulation administered by mouth. Demonstration that a tablet form is effective would further simplify (and encourage) the use of oral vitamin K. A 5 mg vitamin K tablet is available in both Canada and the United States (in Canada the drug is available only after Health Canada approval). For this study, a supply of the 5 mg vitamin K tablets will be obtained from Merck Frosst Incorporated. Study pharmacies will compound this drug to produce matching capsules containing either lactose or lactose and 1.25 mg of vitamin K. This pharmacy will also provide drug packaging and will be responsible for preparing study drug kits which consist of sequentially numbered drug supplies for each clinical centre (following a randomization list provided by the study coordinating centre) and a supply of labeled 1.25 mg capsules (for the cohort study). These supplies will then be distributed, by the coordinating centre to each participating clinical centre.