Shares in Sigma Pharmaceuticals have surged more than 15 per cent after receiving a formal takeover proposal from South Africa's Aspen Pharmacare Holdings group of companies. At 55 cents per Sigma share, the offer values the drugs maker and distributor at $648 million.

In recent trade, Sigma shares were 6.5 cents or 16.46 per cent higher at 46 cents after coming out of a trading suspension.

The formal bid is lower than the initial offer put to Sigma when Aspen approached it in May with a non-binding, indicative and conditional proposal to buy all of the shares in Sigma, at an indicative price of 60 cents per share.
On the new offer the Australian drug maker said, "The Sigma board is considering the proposal and recommends that shareholders take no action at this stage."

"Sigma expects to make a further announcement in relation to the proposal in due course."

Sigma earlier this year reported a net loss of $389 million for the year to January 31. This was followed by the resignations of chief executive Elmo de Alwis, chief financial officer Mark Smith and chairman Dr John Stocker.
In the wake of the loss, the company has decided to sell assets and consider other ways to enrich shareholder value.

According to Sigma's new chairman, Brian Jamieson, Sigma has determined for its net profit after tax in the 2011 fiscal year to go back to similar levels recorded in 2009.