NEW YORK (CNNMoney.com) -- Canadian drugmaker Apotex said Tuesday it launched a generic version of Bristol and Sanofi's blockbuster drug Plavix, even though the company does not have legal clearance to do so.

Bristol-Myers Squibb's (down $1.54 to $21.23, Charts) stock price dropped as much as 8.4 percent in morning trade; its price has plunged 18 percent since its settlement attempt with Apotex was shot down in late July. The stock price for Sanofi-Aventis (down $0.32 to $44.54, Charts) edged down nearly 1 percent, bringing its decline to 11 percent since the failed bid to settle.

Plavix, a blood thinner, is the second-biggest selling drug in the world, with $5.9 billion in 2005 sales. The sales are split between partners New York-based Bristol-Myers and the French drug maker Sanofi-Aventis.

"There should be no mistaking that our decision to launch a generic version of this blockbuster product at risk is a testament to our commitment to patients, consumers, and taxpayers," said Apotex chief executive Barry Sherman, in a press release.

"It's kind of like a slow-motion bus crash," said Les Funtleyder, analyst for Miller Tabak.

Albert Rauch, analyst for A.G. Edwards, downgraded Bristol-Myers to "sell" with the expectation that the drugmaker's stock dividend would be drastically cut. Rauch estimated, a note published Tuesday, that Bristol's expected 2006 EPS would drop 11 percent to $1.10 and the 2007 EPS would plunge 45 percent to 70 cents.

Barbara Ryan, analyst for Deutsche Bank North America who rates Bristol-Myers as a "hold," also published a note projecting a slash in dividend, estimating the Plavix sales represent 40 cents in EPS for Bristol.

The brand-name producers of the drug are locked in a patent battle with Apotex, a Canadian drugmaker. Apotex was approved in January by the Food and Drug Administration to produce and sell the generic version, clopidogrel, in the U.S. However, the company does not have patent clearance to sell the drug.

On July 28, state-level attorneys general shot down an attempt by Bristol-Myers and Sanofi-Aventis to settle with Apotex. The drugmakers had offered to pay Apotex $40 million to hold off generic production until June 1, 2011, just five months prior to the natural expiration date.

"We are currently evaluating our commercial and legal options," said Bristol-Myers spokesman Jeff MacDonald, who said his company attempted to settle in the interest of patients. "We do believe that our patent is valid and has been infringed, so we will vigorously defend our intellectual property."

"The companies are evaluating their legal and commercial options, as well as possible remedies under the agreement with Apotex," Sanofi-Aventis said in a press release.

Sanofi also said the impact of the launch of generic Apotex "cannot be reasonably estimated at this time," and will depend upon volume and pricing.

Generic drugs are priced much cheaper than brand-name drugs, and can prompt an 80 percent plunge in the name-brand price.

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