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UPDATE 1-FDA issues warning letter to Alkermes over opioid addiction treatment ad

(Adds company response in paragraph 6, details from the warning letter in paragraphs 4, 5)

Dec 11 (Reuters) - A print advertisement of Alkermes Plc's addiction treatment, Vivitrol, is false or misleading as it omits important risk information associated with its use, the Food and Drug Administration said in a warning letter http://bit.ly/2LGVKUM to the company.

Users of Vivitrol as a treatment for opioid dependence should be made aware of the vulnerability to potentially fatal overdose at the end of a dosing interval, after missing a dose, or after discontinuing the treatment, the agency said in the letter dated Dec. 2.

Vivitrol, used to prevent a relapse to opioid dependence following detoxification and to treat alcohol dependence, is one of Alkermes' top-selling drugs and brought in $85.2 million in the latest reported quarter.

It blocks the effects of opioids for about 28 days after administration. But as the blockade wanes and eventually dissipates, patients may respond to lower doses of opioids than earlier, leading to potentially life-threatening intoxication, the FDA said.

Cases of overdose with fatal outcomes have been reported in patients who used opioids at the end of a dosing interval, after missing a scheduled dose, or after discontinuing the treatment, the agency said.

Alkermes is committed to working with the FDA to ensure that all promotional materials are fully compliant with applicable laws and regulations, the Dublin-based drugmaker said in an email to Reuters.

Vivitrol is safe and effective for the prevention of relapse to opioid dependence when used as provided in the approved labeling, the FDA said.

Shares of the company were down 2.6% at $21.01. (Reporting by Manojna Maddipatla in Bengaluru; Editing by Sriraj Kalluvila)