Aminoguanidine and alkoxyguanidine compounds, including compounds of the formula:wherein X is O or NR<9 >and R<1>-R<4>, R<6>-R<9>, R<11>, R<12>, R, R, R<c>, Y, Z, n and m are set forth in the specification, as well as hydrates, solvates or pharmaceutically acceptable salts thereof, that inhibit 
proteolytic enzymes such as 
thrombin are described. Also described are methods for preparing the compounds of Formula I. The novel compounds of the present invention are potent inhibitors of 
proteases, especially 
trypsin-like 
serine proteases, such as 
chymotrypsin, 
trypsin, 
thrombin, 
plasmin and factor Xa. Certain of the compounds exhibit 
antithrombotic activity via direct, 
selective inhibition of 
thrombin, or are intermediates useful for forming compounds having 
antithrombotic activity. The invention includes a composition for inhibiting loss of blood platelets, inhibiting formation of blood 
platelet aggregates, inhibiting formation of 
fibrin, inhibiting 
thrombus formation, and inhibiting 
embolus formation in a 
mammal, comprising a compound of the invention in a pharmaceutically acceptable carrier. Other uses of compounds of the invention are as anticoagulants either embedded in or physically linked to materials used in the manufacture of devices used in 
blood collection, 
blood circulation, and blood storage, such as catheters, blood 
dialysis machines, 
blood collection syringes and tubes, blood lines and stents.