Stada Arzneimittel announced that it will start a "structured bidding process" after receiving a number of recent takeover offers. The company said "for this purpose, a data room has been established and the potential bidders – three to date – have been invited to conduct multistage due diligence."

The drugmaker recently confirmed that it received a binding offer from private equity firm Advent International valued at 58 euros ($61.26) per share, or 3.6 billion euros ($3.8 billion). Stada announced earlier this month that it had received two non-binding takeover offers, including an offer from private equity group Cinven valued at 56 euros ($59.15) per share, as well as another from Bain Capital.

According to Stada, "the transparent and fair process, which is open to further interested parties, ensures that all potential bidders receive the same level of information and will have the same opportunity to present their plans for [the company]."

The move comes after activist investor AOC, which is Stada's biggest single shareholder with a more than 5 percent stake, called for the company to conduct its sales process in a non-biased manner.