Spin-offs can bring some serious added value to a company. The idea that the individual parts of a company are worth more than when they're combined may sound counterintuitive to some, but it can actually be true.

Witness the old Abraxis BioScience -- half biotech one-drug wonder, half generic-drug maker. When the company broke apart last November, investors were valuing the centaur of the drug world at just $3.5 billion. Now, the two separate companies, APP Pharmaceuticals (NASDAQ:APPX) and Abraxis BioScience (NASDAQ:ABII), are together worth more than $6 billion. I'd call that a successful spin-off.

But part of that value comes from German company Fresenius and its announcement yesterday of plans to purchase APP Pharmaceuticals for $23 per share -- a 29% premium over the previous closing price. (Before the announcement, the duo was worth about $5.3 billion -- still successful.)

Investors in the purchased generic-drug company could see even more money headed their way. APP Pharmaceuticals will remain a stand-alone company, and if certain targets are met, investors will be entitled to up to an additional $6 per share payable in the second quarter of 2011.

The synergies between APP Pharmaceuticals and Fresenius are pretty good, too. The merger will allow APP Pharmaceuticals to sell its generic-injectable drugs globally without huge start-up costs, and Fresenius gets a foot in the lucrative U.S. generic-drug market. Not a bad deal.

With foreign drug companies snatching up their American counterparts, it's fun to speculate which stateside generic-drug companies might be next. Hospira (NYSE:HSP), a 2004 spin-off of Abbott Labs (NYSE:ABT), might be a takeover target, as could small generic-drug companies like Watson Pharmaceuticals (NYSE:WPI) or Par Pharmaceutical (NYSE:PRX).

The potential for takeover isn't a reason to invest in these companies, but, as APP Pharmaceuticals' investors have found out, it sure is a nice added bonus.

More Foolishness on foreign drug companies coming stateside: