U.S. federal regulators added stronger warnings to a group of bestselling drugs that treat arthritis and other inflammatory diseases, saying they can increase the risk of cancer in children and adolescents.

After more than a year of review, Food and Drug Administration scientists said Tuesday the drugs appear to increase the risk of cancer after they are used beyond 2½ years. The agency studied several dozen reports of cancer in children taking the drugs, some of which were fatal. Half of the cases were lymphomas, a cancer that attacks the immune system.

Health Canada said it was aware of the FDA's action and is reviewing the situation.

"Health Canada takes this potential safety issue with arthritis drugs very seriously," the department said in an emailed response to questions about whether it too would upgrade warnings on the drugs' labels.

Health Canada said new information would be made public as soon as it is available, and in the meantime patients taking the drugs should contact their physicians or pharmacists if they have questions.

Drug makers, regulator probe cancer risk

The drugs are known as tumour necrosis factor blockers and work by neutralizing a protein that, when overproduced, causes inflammation and damage to bones, cartilage and other tissue.

The drugs are prescribed to children with rheumatoid arthritis, inflammatory bowel disorder and Crohn's disease.

The FDA will bolster the "black box" warning on the drugs sold in the U.S., including:

  • Abbott Laboratories' Humira.
  • Johnson & Johnson's Remicade and Simponi.
  • Enbrel, which is co-marketed by Amgen Inc. and Wyeth.

All the products are multibillion-dollar sellers. Enbrel was the biggest moneymaker of the group, with sales of $3.4 billion US last year.

The action also affects Belgian drug maker UCB's Cimizia, which launched in May.

Cimizia is not approved for use in Canada but the other drugs are.

Along with updating the drugs' labels, the FDA is requiring companies to add information about cancer risks to the medication guides given to patients. The FDA said it is also working with the manufacturers to further define the scope of the cancer risk.

J&J said in a statement it "will co-ordinate closely with the FDA to ensure that health-care providers, patients and caregivers are properly informed."

Amgen and Wyeth said they will continue working with regulators to evaluate "the potential risks and benefits" of their drug.

With files from The Canadian Press