On Monday, specialty pharma extraordinaire Cephalon (Nasdaq: CEPH) announced that the European Union finally approved its fentanyl pain drug Fentora. The drug will get the slightly longer name Effentora on the other side of the pond.

Fentora is an oral tablet approved to treat cancer-related pain in patients who aren't responding to other such medications. It's been approved in the U.S. for nearly two years, and in January, the European Medicines Agency issued a positive opinion on the drug. That thumbs-up meant that Fentora would eventually be given full approval, once another two to three months of arbitrary waiting went by -- and now it has.

Sales of Fentora have gained rapidly in the U.S. since its approval in the tail end of 2006. The drug generated $135 million in revenue last year, even in the face of generic competition from Barr Pharmaceuticals (NYSE: BRL) on Cephalon's first-generation Actiq fentanyl compound.

Currently, Fentora is only approved in cancer patients who've already built up a tolerance to opioid pain medications. Cephalon has also been trying to expand Fentora's label into broader populations beyond the cancer patients it's currently approved to treat. In January, Cephalon filed a supplemental new drug application with the FDA to extend Fentora to patients with back, nerve, or other types of chronic pain. An FDA PDUFA date for this marketing application is scheduled for Sept. 13, but investors will get a good idea of the FDA's inclination when the agency releases documents ahead of an advisory panel hearing on May 6.

Peak European sales of Fentora probably won't ascend the same heights as the drug's U.S. sales, because most European Union countries have much tougher reimbursement rules governing how much their national healthcare agencies will pay for drugs. Many of these countries generally make reimbursement rules based on the price paid for a basket of similar drugs, which will severely restrict the sort of price Cephalon can get for Fentora.

Earlier in the year, Cephalon had to send out a warning letter to doctors, after several patients died following improper use of the drug. It remains to be seen how this off-label use by doctors will color the FDA's May advisory panel's view on Fentora in the U.S. Nonetheless, Cephalon now gets to slowly roll the drug out to all the individual European countries, and try to replace as much of the lost generic Actiq sales as possible.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. Barr is an active Stock Advisor pick. The Fool has an A+ disclosure policy.