The U. S. Food and Drug Administration issued a public health advisory Wednesday, alerting doctors and patients about improper and potentially fatal use of pain drug Fentora.

Cephalon Inc., the pharmaceutical company that produces Fentora, sent letters to doctors and health professionals earlier this month advising them to prescribe its powerful painkiller Fentora only as indicated and warning about potentially fatal side effects.

Fentora was approved by the Food and Drug Administration in September 2006 solely for cancer patients already taking morphine or other prescription narcotics for their pain. It contains fentanyl, an analgesic far more potent than morphine.

Cephalon’s mid-September warning said doctors should not substitute Fentora on a one-for-one basis for another drug, an older fentanyl product called Actiq, also produced by Cephalon, which is considerably weaker than Fentora.

Cephalon and the FDA said four deaths had occurred over the summer, apparently through misuse of Fentora.

Two of the victims were patients prescribed Fentora for headaches. Another death involved a suicide, while the fourth was a patient administered the drug outside the recommended dosing.

“None of the reports were in cancer patients, which leads us to believe they were inappropriate candidates for the product,” Cephalon spokeswoman Candace Steele said at the time.

Cephalon and the FDA said the deaths occurred as a result of improper patient selection (patients with an intolerance to painkillers), improper dosing, and/or improper product substitution.

The FDA said at the time it was monitoring the current situation closely.

Wednesday, two weeks later, the FDA reinforced the warning, saying Fentora should only be used for treating breakthrough pain in cancer patients who are opioid-tolerant – cancer patients that experience severe pain that cannot be sufficiently controlled by conventional painkillers like morphine or other powerful drugs.

Cephalon said it is working with the FDA to finalize a new label to reflect new safety messages about the drug.