- Contraindications same as Heparin: 
- ASA (Bleeding) 
- w/ hemorrhagic tendencies 
- pregnancy 
- severe hepatic or renal disease 
- severe hypertension 
- blood dyscrasis 
- Agents which Increase Prothrombin Time: 
- Acetaminophren; 
- Allopurinol 
- ASA
- Steroids 
- Cimetidine
- Indomethacin 
- Flaggyl 
- Hypoglycemics 
- Phenothiazines
- Phenylbutazone 
- Propylthiouracil 
- Quinidine 
- Salicylates 
- Tricyclics 
- Septra; 
- Agents which Decrease Prothrombin Time: 
- Barbituates 
- Oral contraceptives 
- Rifampin 
- Hypothroid patients may be Resistant to Coumarin;
- High levels of Ascorbic acid will interfere with effects