WASHINGTON (Bloomberg) — Covidien Ltd. warned doctors of a risk of leukemia after its drug Phosphocol P 32 was given in an unapproved manner.

Two children with haemophilia developed acute lymphocytic leukaemia about ten months after the drug was administered into a joint to treat bleeding, a method that isn't approved by the US Food and Drug Administration, Covidien said in a letter posted today on the FDA's Web site.

The drug is injected to treat the leaking of fluids inside the body caused by cancer.

Prescribing information for the drug has been revised to reflect the new warning, according to Covidien.

Covidien of Mansfield, Massachusetts, fell 29 cents, or less than one percent, to $54.25 at 3:13 p.m. in New York Stock Exchange composite trading after falling as much as 14 percent when the Covidien letter was posted.