A new study suggests low-molecular weight heparin may be more effective at treating blood clots in cancer patients than the commonly used anti-clotting drug warfarin (Coumadin). Researchers from Canada and several other countries found the heparin further reduced the chance of a new blood clot forming and didn’t lead to any more bleeding.

One expert suggests low-molecular weight heparin should therefore become standard treatment for blood clots in cancer patients.

Blood clots are a major problem for cancer patients, because treatments for the disease can leave them more susceptible to this serious condition. The clots often develop in the veins of the leg and can travel to the major blood vessels of the lung, where they can be fatal.

Blood clots can be treated with warfarin, a pill that blocks the body’s ability to make the proteins needed for clots to develop. Another option is heparin, a substance that directly blocks the clotting process. Heparin can only be given by injection.

In the past, heparin was difficult to use because it required very careful monitoring. Now, purified, low-molecular weight versions of this drug are available that do not need such careful monitoring. Even when warfarin is going to be used to treat a patient with a blood clot, heparin is usually given for the first few days because it works immediately. Warfarin takes several days to begin working.

Although treatment with warfarin is usually effective in most people with blood clots, it is less effective in cancer patients. Also, treatment with warfarin is tricky because the level of anticoagulation (anti-clotting) is affected by poor diet and liver malfunction, common problems in cancer patients.

Because of this, Agnes Lee, MD, of McMaster University in Canada, along with researchers from the US, Australia, England and the Netherlands examined whether dalteparin, a low-molecular weight heparin, would do a better job than warfarin in cancer patients with blood clots. Their results were published in the New England Journal of Medicine (Vol. 349, No. 2: 146-153).

The researchers studied 676 cancer patients who had a recently diagnosed blood clot in either a leg or lung. Although most patients had widespread cancer, only a small number were bed-ridden. Patients with many different types of cancers were enrolled in the study.

All patients were started on daily dalteparin injections to get their clots quickly controlled. After about a week, half the patients stopped the dalteparin, and instead received warfarin or a similar oral anticoagulant. The remaining patients continued on the dalteparin. All patients were treated for a total of six months.

By the end of the six-month period, 53 patients on the warfarin or warfarin-like drug had experienced a recurrent blood clot. This was nearly twice the number of recurrent blood clots (27) seen in the dalteparin-treated patients. A total of 12 patients died because of a blood clot traveling to the lung. Five had gotten dalteparin and seven received the oral anticoagulant.

Bleeding problems were about the same in each group. Likewise, there was no difference in overall mortality. By the end of the study, about 40 percent of patients in each group had died.

One potential problem with the use of dalteparin is that it is given by daily injection. The researchers found, however, that patients had no problem with self-injection. Another problem is cost: Dalteparin is much more expensive than oral anticoagulants.

But those costs may be overestimated, according to clotting expert Rodger Bick, MD, PhD, of the University of Texas Southwestern Medical School. In an editorial accompanying the study, Bick pointed out that fewer patients on dalteparin developed recurrent blood clots that needed treatment. Those savings compensate for the high cost of the drug. Also, he added, the frequent blood tests needed to monitor patients on warfarin are unnecessary for patients on dalteparin, which is a further savings.

Bick concluded that low-molecular weight heparin should become the anticoagulant of choice in cancer patients with blood clots.