Several manufacturers of a patch containing a chronic pain drug are changing dosing instructions to address potential overdose risks.

The five manufacturers of Fentanyl Transdermal Systems and Health Canada said the patches contain a high concentration of the long-acting narcotic fentanyl.

Last February, 25 mcg/hr Duragesic patches sold by Janssen-Ortho Inc. and 25 mcg/hr Ran Fentanyl Transdermal System Patches sold by Ranbaxy Laboratories were voluntarily recalled for overdose risks.

The patches treat persistent, moderate to severe chronic pain in people already taking narcotic pain relievers.

Fentanyl can cause serious and life-threatening breathing problems if too much is taken, Health Canada warned Wednesday.

The new dose conversion guidelines are to be used to convert adult patients from their current oral or injection therapy to the fentanyl transdermal patch, says an advisory to health-care professionals.

People using the patches without any problems should not stop or decrease their dosage without talking to their doctors.

The notice applies to:

• Duragesic ® (Fentanyl Transdermal Systems).
• CO Fentanyl.
• Novo-Fentanyl.
• RAN-Fentanyl Transdermal Systems.
• Ratio-Fentanyl Transdermal System.

Patients using fentanyl patches should seek emergency medical help immediately if they:

• Have trouble breathing, or have slow or shallow breathing.
• Have a slow heartbeat.
• Have severe sleepiness.
• Have cold, clammy skin.
• Feel faint, dizzy, confused or cannot think, walk, or talk normally.
• Have a seizure.
• Have hallucinations.

Any serious or unexpected adverse reactions in patients receiving fentanyl transdermal systems should be reported to the manufacturers or Health Canada.