On Friday, Merck & Co. agreed to pay $4.85 billion to settle thousands of lawsuits regarding their painkiller Vioxx.

If accepted, it would end 45,000 to 50,000 personal injury lawsuits dealing with Vioxx users who suffered an ischemic stroke or heart attack.

On September 30, 2004, Vioxx was pulled from the market after researchers discovered that the popular arthritis treatment actually doubled the risk of heart attacks and strokes.

Plaintiffs hoping to qualify for a settlement must have filed their claim by Thursday and met other criteria, including medical proof that they suffered a heart attack or stroke. Also, the deal does not include people in foriegn countries. Furthermore, potential plaintiffs must be able to show that they received at least 30 Vioxx pills, and that they received enough pills to support a presumption that they were ingested within two weeks before the injury

Merck had previously claimed that Vioxx could only cause harm after 18 months of use, however, independent scientists and plaintiffs lawyers dismissed those claims.

Merck maintained that the agreement is not a class action settlement and had stated as recently as last month that every case would be fought individually. Merck, however, changed its stance on Friday with the proposed settlement.

To date, Merck had won 10 of 15 civil court verdicts.

The deal becomes binding only if 85 percent of the plaintiffs in key categories agree to the deal: all pending heart attack and ischemic stroke cases, all cases involving deaths and all cases alleging more than 12 months of Vioxx use.

$4 billion will go to heart claimants while the rest is reserved for stroke claimants.

Victim payouts will depend on the severity of injuries, length of time that Vioxx was used and each person’s cardiovascular disease. Payments could start as early as August 2008.