Gentiva Health Services Inc GTIV.O said it adopted a poison pill, more than a week after the home healthcare services provider rejected a $533-million hostile bid from hospital operator Kindred Healthcare Inc (KND.N).
Gentiva set a 15 percent trigger for the rights plan, which will expire on May 20, 2015.
Gentiva rejected Kindred's $14-per-share offer on May 15, saying it undervalued the company.
"Poison pills" are designed to stop hostile takeover attempts by triggering the issue of new shares that dilute the holdings of investors who exceed a set threshold.
Gentiva's shares closed at $13.68 on the Nasdaq on Friday. They have gained 60 percent since the offer was made public.
(Reporting By Vrinda Manocha in Bangalore; Editing by Sriraj Kalluvila)