Therapeutic doses of warfarin are minuscule: 2mg to 10mg for a 100kg person. The actual dosage depends upon an individual's diet and metabolism, as well as body weight. In fact, body weight is not a major factor. A 150kg person may require 2mg while a 75kg person may require 10mg for the same therapeutic effect.
There are very few good alternatives to sodium warfarin treatment. In some cases, a doctor may prescribe low-molecular-weight heparin (LMWH). I do not know the issues about long-term effectiveness of LMWH, but the fact that it requires two injections per day, subcutaneous, at fairly precise 12-hour intervals, precludes its use for most people. I've done it in the short-term (post-surgical recovery while the warfarin is ramping up). I wouldn't want to have to do it every day.
The complementary problem for people on warfarin therapy is that it is necessary to keep a balanced intake of Vitamin K. Many foods are high in Vitamin K, including shrimp and spinach, and an unbalanced intake of Vitamin K will cause the prothrombin times to vary wildly. This is not to say that foods containing Vitamin K must be avoided; merely that the intake should be reasonably constant, so the warfarin dosage can be adjusted to compensate for it.
Coagulant drugs or Vitamin K1 have been suggested as possible antidotes for pets accidentially exposed to anticoagulant poisons. In addition, since some of these poisons act by inhibiting liver enzymes, a blood transfusion (with the products of the correct enzymes present) can save a person who inadvertently takes them, an advantage over some older poisons.
For example, an occasional spinach salad is not considered dangerous, but a spinach salad every night for two weeks would not be a good idea, particularly if there was a prothrombin-clotting-time test taken just at the end of those two weeks. Besides the risk that the sustained Vitamin K intake would cause (due to lowered clotting time), an adjustment made to the dosage followed by a discontinuance of the intake would result in a significantly raised clotting time. So the key is to maintain a reasonably constant Vitamin K intake.
