Pfizer Inc. has recalled an opioid painkiller obtained when it purchased King Pharmaceuticals. Embeda, which has annual sales of less than $70 million, was recalled in the United States because of a stability defect found in the extended-release product during routine testing. The drug contains pellets of morphine that surround naltrexone, a chemical which blocks opiate effects if the product is crushed or chewed — thereby deterring misuse or abuse. The naltrexone component was shown to have degraded to unacceptable degrees in samples of Embeda that were tested. The problem is unlikely to pose a safety risk and patients can continue taking the drug as prescribed, according to the drugmaker. Embeda, approved by U.S. regulators in August 2009, was recalled three times last year due to other formulation problems, all relating to how it dissolves.