A new class of blood-thinning drugs is winning market share from decades-old warfarin, a commonly prescribed drug used to reduce blood clots in patients with heart disease or that have undergone hip or knee replacement surgery. So far, Boehringer Ingelheim has been the most successful at carving sales away from warfarin with its $1 billion-a-year Pradaxa. Bayer (BAYR.Y 3.27%) and Johnson & Johnson (JNJ -0.43%) are also doing well with Xarelto. However, the real surprise may be Pfizer (PFE -0.07%) and Bristol-Myers Squibb's (BMY) Eliquis, which is gaining ground thanks to a big marketing push.

Picking up speed
Warfarin is riddled with drawbacks including regular monitoring, dose adjustments, and risks of brain hemorrhage. That suggests new treatments can not only replace warfarin as the go-to blood thinner, but also expand the market altogether; it is estimated that half of those who should be on anti-coagulants don't take them because of warfarin's risks.

The three newer drugs work differently from warfarin, which reduces clots by blocking vitamin K, a key clotting factor. Eliquis and Xarelto inhibit the production of thrombin by targeting an enzyme called Factor Xa. Alternatively, Pradaxa binds to thrombin to prevent blood clots from forming.

Pradaxa, the first of the three to win the FDA's go-ahead, has the early lead in terms of sales. Xarelto has also seen impressive growth in the past year, too. But Eliquis is the only one of the three that's been proved to reduce mortality. Patients on Eliquis saw a lower risk of gastrointestinal bleeding during studies as well.

Those advantages may finally be winning over doctors, as Eliquis sales have jumped sequentially since the spring. Bristol-Myers reported Eliquis revenue of $12 million in the second quarter, $44 million in the third quarter, and $71 million in the fourth quarter. As a result, global sales of the drug improved to $146 million in 2013 from just $2 million in 2012. 

That's still a far cry below the 600 million Euros' worth of twice-daily Pradaxa that Boehringer sold in the first six months of 2013. And it's well below the $271 million Johnson reported in Q4 sales for once-daily Xarelto. But it's a good step in the right direction for the twice-daily Eliquis.

Fool-worthy final thoughts
All three are approved for use in elective knee and hip surgery or in prevention of stroke or systematic embolism with non-valvular atrial fibrillation. Xarelto has an additional approved indication for use in deep vein thrombosis and pulmonary embolism. But Pfizer and Bristol filed for Eliquis approval for those indications in December, suggesting that advantage won't exist for long.

All three drugs do have drawbacks versus warfarin. The most notable is the absence of effective countermeasures to reverse their effects. That means they're not able to be used in some patients who are at a greater risk of bleeding. The new drugs also have a shorter half-life than warfarin, which could pose problems for patients who fail to take the drugs as prescribed. And since patients taking Pradaxa, Xarelto, and Eliquis aren't monitored or easily tested, it can be harder to treat patients who do hemorrhage, because doctors may have a tougher time determining whether the drugs are still in the patient's bloodstream.

Those drawbacks don't even address the issue of the drug's higher cost. All three carry price tags far higher than the age-old warfarin. But insurers don't appear to be balking, and with likely label expansion and eventual anecdotes, Eliquis may eventually find that it lives up to analysts' pre-launch predictions and becomes a blockbuster drug.