Anticoagulants--blood thinners--reduce chances of harmful blood clots. Behaviors of the classic drugs, aspirin and precursors of warfarin, were discovered by accident. Aspirin was developed as an analgesic. Its effects at blood thinning were noticed in the 1930s; it was never a prescription drug. Warfarin was patented as rat poison in 1948; Endo obtained FDA approval in 1954 as a prescription drug named Coumadin. Since then, several similar brand-name drugs have been introduced, all minor variations.

The main hazard of anticoagulants is not a "side effect." It is the main effect: increased risk of harmful bleeding--such as unchecked gastrointestinal, menstrual and wound blood flows. While anticoagulants reduce risk of ischemic stroke--from a clot--they increase risk of hemorrhagic stroke--from unchecked blood flow. Treatments usually include frequent measurement of clot formation to maintain a balance, most often the "prothrombin time" blood test at weekly to monthly intervals. [ Warfarin, U.S. National Library of Medicine, 2010, at http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000634/ ]

A critical element in arresting health hazards from anticoagulant overdose is prompt administration of an antidote. For warfarin, the normal antidote is vitamin K. It can restore clot formation in minutes and check harmful bleeding. The frequency of hemorrhagic stroke is many times the frequency of ischemic stroke, and availability of an antidote can be literally life-saving.

Typical obsession of U.S. physicians with prescription drugs led to neglect of aspirin as an anticoagulant. A recent, large, fully controlled clinical trial showed that aspirin is as effective as warfarin for treating congestive heart failure--the most common use of warfarin. [ Nicholas Bakalar, Aspirin seen to be as effective as warfarin, New York Times, May 7, 2012, at http://well.blogs.nytimes.com/2012/05/07/aspirin-prevents-blood-clots-in-heart-failure/ ]

The last two years have seen a new generation of prescription anticoagulants. While they may provide some improvements over aspirin and warfarin, the improvements are modest in scale, and the new anticoagulants are turning out to carry hazards similar to the old ones. An additional hazard is that, unlike warfarin, none of the new anticoagulants has a known antidote. Typical costs are about 20 times warfarin, whose cost is at least 20 times aspirin:

* Pradaxa, FDA approval 2010, Boehringer Ingelheim

* Xarelto, FDA approval 2011, J&J and Bayer

* Eliquis, pending, Pfizer and Bristol-Myers Squibb