UPDATE 1-Cumberland says FDA extends liver drug review date

* FDA extends review date by 3 months to December

* Co trying to get drug approved for liver failure

* Drug already approved to treat acetaminophen overdose

* Shares down 10 pct in after-hours trade

Aug 20 (Reuters) - Cumberland Pharmaceuticals Inc CPIX.O said the U.S. regulator extended the review date for the company's drug for acute liver failure by three months to December, sending its shares down 10 percent after market.

The drug, Acetadote, is already approved to treat the overdose of a widely used over-the-counter painkiller, acetaminophen, which can lead to liver damage. Cumberland is trying to get the drug, generically known as acetylcysteine, approved for acute liver failure induced by reasons other than acetaminophen overdose.

Shares of the Nashville, Tennessee-based company were down 10 percent to $5.40 in after-hours trade. The shares, which have lost more than half of their value over the past six months, closed at $6.02 Friday on Nasdaq. (Reporting by Esha Dey in Bangalore; Editing by Unnikrishnan Nair)