The intensifying pursuit, which has already boosted Stada shares by about 70 percent in the past year, centers around the buyout firms' conviction that they can slash its costs and boost earnings.
The company's three-year average operating profit margin of 11 percent is among the lowest for makers of cheap copycat drugs globally, according to data compiled by Bloomberg. Streamlining the manufacturing, breaking up the firm or firing some of its more than 10,000 employees are potential targets for the buyers.
"Obviously, there's potential for improvement," said Bernhard Weininger, a Frankfurt-based analyst with Independent Research GmbH. "That's the main reason why Stada is of great interest for financial investors."
The feeding frenzy is driven in part by private equity firms' search for fresh targets as a cycle of buying and selling each others' assets in so-called secondary buyouts dry up, executives at the SuperReturn International conference in Berlin said earlier this month.
Many private equity firms have already sold their vintage assets, which are businesses that have been held for about five years and are ready to go on the block, while other companies in their portfolios aren't yet ripe for an exit.
Stada's international ambitions have also left it more vulnerable. An expansion into Serbia and Russia -- undertaken about a decade ago to spur growth -- has proven to be a millstone in the past three years. The Bad Vilbel-based company, which will report 2016 earnings next week, has said this for the first nine months of the year:
• In Russia, sales of branded drugs slumped 30 percent, though generics rose 31 percent
• In Serbia, price cuts helped push sales of copycat drugs down 28 percent
• Vietnam was a bright spot, with sales of branded drugs rising 15 percent
Its suitors may face other hurdles as well.
While the departure of Chief Executive Hartmut Retzlaff in June after more than 20 years at the helm helped stoke speculation about Stada being up for sale, Chairman Carl-Ferdinand Oetker in recent days has proved to be no pushover.
Oetker, who heads a committee on the supervisory board to oversee the bidding process, hit the brakes on deal negotiations this week by refusing to approve additional due diligence by the potential buyers.
That's because their bids don't reflect the fundamental value of the company, Stada said in a statement late Thursday.
Stada shares dropped as much as 2.7 percent before trading down 0.8 percent to 56.39 euros as of 11:18 a.m. in Frankfurt.