Cancer patients taking certain bone drugs called bisphosphonates may develop a severe form of bone damage in the jaw if they get major dental work during their therapy, the FDA and a drug company said this week. Novartis Oncology said patients taking certain drugs called bisphosphonates should avoid invasive dental work, if possible.

Novartis manufactures the bisphosphonates Aredia (pamidronate disodium) and Zometa (zoledronic acid). It sent letters to doctors late last month advising them that some cancer patients on these drugs had experienced osteonecrosis of the jaw. This condition disrupts the blood supply to the bone, causing tiny breaks that can eventually lead to a total collapse of the bone.

Many of the patients who developed problems were taking chemotherapy and corticosteroids in addition to the bone drugs, and many had signs of infection in the jaw, the company said.

Having major dental work, like a tooth extraction, may contribute to the problem, Novartis said. Most of the cancer patients who developed osteonecrosis of the jaw had also had some type of dental work.

The FDA and Novartis said patients should consider having a dental exam and any needed procedures before beginning therapy with bisphosphonates. If possible, patients should avoid invasive dental procedures while getting treatment. It is not known whether stopping the drugs will prevent the problem if a patient needs dental work during therapy.

Cancer and certain of its treatments (chemotherapy, radiation, corticosteroids) are already well-known risk factors for osteonecrosis of the jaw, Novartis said. Other problems like anemia, blood clotting disorders, infection, and mouth diseases can also raise the risk.