Are There Any Specific Drug Interactions With Fentanyl Patches (50

Are there any specific drug interactions with Fentanyl Patches (50 mcg/hr.)? I tried to have the prescription filled with one for Percocet 10/325 mg. PRN breakthrough pain. They refused to fill the Fentanyl with the reason there was a drug interaction with Cardizem, which I take occasionally for hypertension not responding to my regular medication. I have had this combination filled before, but I also learned that the pharmacy was being sued by the government for the number of opiate prescriptions filled. I've gotten them filled there for >7 years.
Thank you for your help.