Safety Matters: New Anticoagulants

Blood clots develop in the veins or arteries, and while they are essential in preventing excessive bleeding when these vessels become injured, they also can be harmful.

Anticoagulants are pharmacologic agents used to keep blood from clotting and are given to patients to prevent or break up blood clots.

“Until rather recently, there were only two anticoagulants, Heparin and Warfarin, which is also known as Coumadin,” said Dr. Carolyn Chesney, ______ .”

These anticoagulants were discovered in the early 1900s. Heparin was not introduced into clinical practice until 1937, while the Vitamin K antagonist Coumadin was not clinically used until the 1950s, said Chesney.

Heparin was isolated from the liver in 1918. This substance had to be used in the hospital setting and the dose had to be monitored frequently.

“Too low of a dose and the patient was not anti-coagulated and could experience more clotting and even death,” said Chesney. “Too high of a dose and the patient could bleed, possible fatally.”

On the other hand, Coumadin was the first oral anticoagulant, derived from Dicoumerol in sweet clover and first used in rat poison. Patients were able to take this medication at home, but it required much monitoring. Because Coumadin is a Vitamin K antagonist, the anticoagulant is affected by foods high in Vitamin K, possibly inhibiting the effect of Warfarin and making it less effective.

“The first oral anticoagulant that did not have to be monitored was introduced about 10 years ago but was available in the U.S. because it caused serious liver toxicity early on,” said Chesney. “[It was] withdrawn from the market.”

However, in the last two years, several new oral anticoagulants have now become available for several specific diagnosis, such as atrial fibrillation or deep vein thrombosis treatment.

“These products are marketed conveniently because they can be taken by mouth and do not require monitoring,” said Chesney. “At this time, they are expensive compared to Warfarin.”

While these newer anticoagulants are more convenient, there are still side-effects.

“The major problem with the newer agents is that if a patient should experience a bleeding episode, there is no antidote which can predictable reverse the anticoagulant effect,” said Chesney. “Therefore, there have been deaths due to bleeding.”

Compliance is another major risk associated with these new medications. Patients may miss a dose and belittle how important this is.

“However, because of the short half-life of the drug, the patient may not be sufficiently anti-coagulated and experience a thrombosis or stroke in the case of atrial fibrillation,” said Chesney. “It is very important that the physician explain this information to the patient and their caregivers.