It isn't enough that Abbott Labs' (NYSE:ABT) drug-eluting stent, Xience V, is wiping the floor with Boston Scientific's (NYSE:BSX) Taxus in the marketplace. In late 2007, Taxus had a greater than 50% market share for drug-eluting stents, but that has declined to 27% recently, behind Xience V's 50% share. Xience's share is about evenly split between Abbott's Xience V and the same stent sold by Boston Scientific under the name Promus. Xience V is also continuing to do it at scientific meetings -- which, of course, will lead to Xience taking even more market share.

At the American College of Cardiology meeting this weekend, Abbott presented data from an ongoing head-to-head trial of Xience and Taxus, and the results look even better than the earlier two-year data point. At three years after implantation, Xience maintained its rate of major cardiovascular events, such as heart attacks, at 6.4%, but the rate for Taxus went up from 10.5% at year two to 14.9% at year three. Talk about kicking a guy while he's down.

This continued strong showing should help Xience continue to compete well, especially against Medtronic's (NYSE:MDT) Endeavor, a fellow newcomer to the U.S. market. I'd say the data pretty much puts a nail in the coffin for Johnson & Johnson's (NYSE:JNJ) Cypher, the first drug-eluting stent on the market, which looks to be well past its prime. The health-care giant does have a next-generation stent in the works, though.

All isn't completely lost for Boston Scientific, however, as it gets to sell Promus -- albeit with some royalties going back to Abbott. Last quarter, domestic sales of Promus and Taxus were about equal, but as the data sinks in for cardiologists, I expect we'll see a continuing trend toward more sales of Promus (and Xience) at the expense of Taxus.

Pivotal trials are necessary for drug and medical device makers to get their products past the FDA and onto the market, but it's just as important for investors to pay attention to the post-marketing trials. The results of those trials can often determine whether the product becomes a blockbuster or just languishes in oblivion. It can even cause a bidding war, as seen with Gilead Sciences' (NASDAQ:GILD) and Astellas Pharma's pursuit of CV Therapeutics' (NASDAQ:CVTX) Ranexa.

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Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. CV Therapeutics is a former Rule Breakers recommendation. The Fool has a disclosure policy.