LONDON--AstraZeneca PLC (AZN) Monday said it had settled a long-running patent lawsuit with three generic drug makers, in a move which will help safeguard revenue from top-selling drug Crestor until 2016.

The Anglo-Swedish drugs giant said Watson Laboratories Inc., Actavis Inc. (ACT) and EGIS Pharmaceutical PLC (EGIS.BU) had conceded that the patent on the rosuvastatin zinc version of Crestor, one of the world's biggest-selling statins, was valid.

The settlement will give AstraZeneca some help shoring up revenues which are being sharply eroded due to the loss of patent protection on Crestor and others such as antipsychotic drug Seroquel. Crestor generated $6.25 billion of sales in 2012, down from $6.6 billion in 2011 after losing patent protection in certain regions.

This is the latest in a large number of lawsuits relating to Crestor. AstraZeneca won a court case last year that reaffirmed its protection on a patent covering a different and more widely used version of Crestor based on the active ingredient rosuvastatin calcium, through 2016.

AstraZeneca said its agreement with Watson Pharmaceuticals means Watson can begin selling a generic version of the drug, with 39% of net sale revenue going to AstraZeneca, until the end of paediatric exclusivity on July 8, 2016, giving Watson Laboratories a three-month window ahead of other generic drug-makers.

Several other generic drug makers have filed for the right to launch copycat versions of Crestor before its patents expire. The lawsuits argued that AstraZeneca's original patent on rosuvastatin calcium was invalid because the original patent applicant for the drug, Shionogi & Co. Ltd. (4507.TO), withheld certain information from the patent office.

A U.S. Federal Appeals court last December found there wasn't clear evidence that Shionogi patent staff deliberately withheld information and upheld the patent on Crestor.

-Write to jessica.hodgson@dowjones.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires