Omnicare Inc. has extended its offer to buy all outstanding shares of pharmacy management services company PharMerica Corp. until Jan. 20 after only about 9 percent of shares had been tendered and not withdrawn by a Dec. 2 deadline.

Omnicare, which dispenses drugs for nursing homes and other long-term care centers, is offering to buy PharMerica shares for $15 each. PharMerica, based in Louisville, Ky., opposes the deal and has said the price is too low.

Covington, Ky.-based Omnicare launched the tender offer in September after going public with its $457 million hostile takeover bid in August. The $15 per share price represents a 37 percent premium to PharMerica's closing price the day before Omnicare went public with its offer.

PharMerica shares have been trading above the $15 offered price since late October, peaking at $16.45 in mid-November. In midday trading Monday, its shares rose 17 cents to $15.47 per share.

The Federal Trade Commission is evaluating the proposed deal. Omnicare said Monday it will not consummate the deal before Jan. 19, unless the FTC has closed its investigation.

PharMerica operates institutional pharmacies in 44 states, serving nursing centers, hospitals and other long-term care providers. It was formed by the July 2007 spin-off and combination of the institutional pharmacy businesses of AmerisourceBergen Corp. and Kindred Healthcare Inc. into a stand-alone company.

Shares of Omnicare rose 80 cents, or 2.4 percent, to $33.94 in midday trading.