Arthritis Drugs Put a Hurt on Merck and Pfizer

Updated from 11:45 a.m. EDT

Shares of Merck(MRK Quote) and Pfizer(PFE Quote) declined Thursday as criticism continued about the class of arthritis and painkiller drugs known as COX-2 inhibitors.

Shares of Merck, which last week said it was pulling its COX-2 drug Vioxx from the market immediately, fell another 66 cents, or 2.1%, to $31.01. The stock dropped as low as $30.18, a new 52-week low. The stock closed at $45.07 on Sept. 29, the day before the company said it was removing Vioxx from the market because it presented a higher risk of heart problems.

Shares of Pfizer, which issued a detailed account Saturday asserting that its Celebrex and Bextra COX-2 drugs are safe, fell $1.27, or 4.1%, to $29.91. The stock sank as low as $28.60, also a new 52-week low. Analysts had expected Pfizer to capitalize on Merck's Vioxx woes. But Pfizer was trading Thursday just below the level it closed on Sept. 29. ...