MUMBAI (Reuters) - Shares in Orchid Pharmaceuticals & Chemicals Ltd (ORCD.BO: Quote, Profile, Research) gained nearly a quarter of its value on Monday before easing to end 15.5 percent higher on news privately held Solrex Pharmaceuticals Co had bought 8.1 percent last week, analysts said.

The shares fell to a near-four-and-a-half-year low in March after Bear Stearns BSC.N sold its stake in the firm and Orchid's Managing Director Raghavendra Rao was forced to sell 7.9 percent of his and his family's stake to meet margin calls.

"The shares' downfall had happened due to reasons which were not fundamental to the company," said Angel Broking analyst Sarabjit Kour Nangra. "So any news would push up the stock."

Solrex acquired the 8.1 percent stake last week in two chunks from the open market, Rao told Reuters.

A business news channel, CNBC TV-18, reported that Solrex was a partnership firm floated by the promoters of larger rival Ranbaxy Laboratories Ltd (RANB.BO: Quote, Profile, Research).

A Ranbaxy spokesman delined comment while Rao said he did not know anything beyond the name of the buyer.

Ranbaxy shares which stayed up through the day, ended 5.6 percent at 483.85 rupees.

Rao's and his family's holding in Orchid has dropped to about 16 percent after the share sale in March.

Ranbaxy had invested in several domestic drugmakers as part of its strategy to widen its product basket or acquire a manufacturing unit, an analyst who declined to be named said.