On Wednesday, tests conducted by the Food and Drug Administration revealed that fake versions of Lipitor and other widely used prescription drugs are available on the Internet through Web sites linked to a Canadian pharmacy.

The FDA cautioned consumers who bought drugs through the 10 Web sites and said they should not use the medications because they may not be safe. The sites include rxnorth.com, canadiandrugstore.com and rxbyfax.com

The Food and Drug Administration is advising consumers not to purchase prescription drugs from Web sites that have their orders filled from Canadian companies reportedly selling counterfeit medications.

The FDA is investigating reports that Mediplan Prescription Plus Pharmacy or Mediplan Global Health in Manitoba, Canada sold fake drugs to U.S. consumers.

It is coordinating its efforts with international law enforcement authorities

A Canadian study, which suggests that Merck's disputed arthritis painkiller, Vioxx, increases heart attack risk in first few weeks of use, may pose problems for the pharmaceutical giant.

The study, reported in the Canadian Medical Association Journal, is based on the medical records of 3,947 patients over the age of 65 who took Vioxx, and 239 of them had heart attacks

A new study shows that patients taking Celebrex are nearly twice as likely to experience a heart attack as people using other drugs to treat arthritis pain.

Researchers at the New Zealand Medical Research Institute analyzed six studies involving 12,780 patients. They found that patients taking Celebrex had a 1.88-fold increase risk of a heart attack compared to those taking other painkillers

A federal judge on Friday upheld the validity of two key U.S. patents on Pfizer Inc.'s Lipitor cholesterol drug, blocking a generic version of the medicine that threatened the company's largest source of revenue. The decision, which lifted Pfizer shares 10 percent, dealt a setback to Indian drug maker Ranbaxy Laboratories Ltd which had hoped to introduce the cheaper copycat as soon as 2008. Pfizer will now have patent protection on the world's best-selling drug through June 2011. Ranbaxy vowed to appeal the decision.

Lipitor is Pfizer's pillar of strength as the company's revenue growth and earnings continue to dwindle due to a raft of problems. Sales of Pfizer's Celebrex have been cut almost in half due to safety concerns. Revenue from Bextra was eliminated when the drug was withdrawn after being linked to a deadly skin condition