The Food and Drug Administration issued a product safety alert to pain management specialists and health-care professionals Thursday after

Cephalon

(CEPH)

issued letters warning that it recently learned of serious adverse events, including deaths, that have occurred in patients treated with Fentora, the company's treatment used to manage breakthrough pain (BTP) in cancer patients.

The deaths occurred as a result of improper patient selection, improper dosing and/or improper product substitution, according to the company. In a

letter to doctors and a

letter to health care professionals issued on Sept. 10, Cephalon provided safety information and instructions to prevent those improper uses and reduce the risk of respiratory depression.

Cephalon warned in the letters not to substitute Fentora for Actiq or other fentanyl-containing products, and not to prescribe the pain treatment to patients who are opioid non-tolerant, or who have acute pain, postoperative pain, headache/migraine or sports injuries.

In the letter, Cephalon said it has revised the patient selection criteria and dosing instructions for Fentora and will be updating its package insert shortly.

Cephalon shares slid $4.06, or 5.3%, to $72.48 in recent trading Thursday.