Warfarin (also known under the brand names Coumadin, Jantoven, Marevan, Lawarin, and Waran) is an anticoagulant. It was initially marketed as a pesticide against rats and mice and is still popular for this purpose, although more potent poisons such as brodifacoum have since been developed. A few years after its introduction, warfarin was found to be effective and relatively safe for preventing thrombosis and embolism (abnormal formation and migration of blood clots) in many disorders. It was approved for use as a medication in the early 1950s and has remained popular ever since; warfarin is the most widely prescribed anticoagulant drug in North America.
Warfarin is a synthetic derivative of coumarin, a chemical found naturally in many plants, notably woodruff (''Galium odoratum'', Rubiaceae), and at lower levels in licorice, lavender, and various other species. Warfarin and related coumarins decrease blood coagulation by inhibiting vitamin K epoxide reductase, an enzyme that recycles oxidized vitamin K to its reduced form after it has participated in the carboxylation of several blood coagulation proteins, mainly prothrombin and factor VII. For this reason, drugs in this class are also referred to as vitamin K antagonists. In 1921, Frank Schofield, a Canadian veterinary pathologist, determined that the cattle were ingesting mouldy silage made from sweet clover that functioned as a potent anticoagulant. He separated good clover stalks and damaged clover stalks from the same hay mow, and fed each to a different rabbit. The rabbit that had ingested the good stalks remained well, but the rabbit that had ingested the damaged stalks died from a haemorrhagic illness. A duplicate experiment with a different sample of clover hay produced the same result. This report led to the subsequent research that led to dicoumarol's discovery. Coumarins are now known to be present in many plants. The smell of freshly cut grass or hay is due to a coumarin.
The identity of the anticoagulant substance in moldy sweet clover remained a mystery until 1940 when Karl Paul Link and his lab of chemists working at the University of Wisconsin set out to isolate and characterize the hemorrhagic agent from the spoiled hay. It took five years for Link's student Harold A. Campbell to recover 6 mg of crystalline anticoagulant. Next, Link's student Mark A. Stahmann took over the project and initiated a large scale extraction, isolating 1.8 g of recrystallized anticoagulant in about 4 months. This was enough material for Stahmann and Charles F. Huebner to check their results against Campbell's and to thoroughly characterize the compound. Through degradation experiments they established that the anticoagulant was 3,3'-methylenebis-(4-hydroxycoumarin), which they later named dicoumarol. They confirmed their results by synthesizing dicumarol and proving that it was identical to the naturally occurring agent. Over the next few years, numerous similar chemicals were found to have the same anticoagulant properties. The first of these to be widely commercialized was dicoumarol, patented in 1941. Link continued working on developing more potent coumarin-based anticoagulants for use as rodent poisons, resulting in warfarin in 1948. (The name warfarin stems from the acronym ''WARF'', for ''Wisconsin Alumni Research Foundation'' + the ending ''-arin'' indicating its link with coumarin.) Warfarin was first registered for use as a rodenticide in the US in 1948, and was immediately popular; although it was developed by Link, the WARF financially supported the research and was assigned the patent.
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Last Updated: Feb 1, 2011