Phenprocoumon Ranitidine

In one study in 10 patients stabilised on phenprocoumon, ranitidine 150 mg twice daily for 14 days had no effect on anticoagulation or on phenprocoumon plasma levels. ... 

The anticoagulant effects of warfarin can be increased by cimeti-dine. The effect is generally minor to modest, although severe bleeding has been reported in a few cases. Acenocoumarol seems to interact similarly, but phenprocoumon appears not to be affected. In one patient the effects of phenindione were modestly increased by cimetidine. Famotidine, nizatidine, ranitidine and roxatidine normally do not appear to interact, although isolated cases of bleeding have been reported. 

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