Oct 11 (Reuters) - Pacira BioSciences will buy Flexion Therapeutics Inc for about $427.5 million to gain access to Flexion's non-opioid pain drug, the companies said on Monday.

Pacira will buy Flexion's outstanding shares for $8.50 per share, a 47% premium to their last closing price.

In addition, the deal also includes a "contingent value right" where Flexion shareholders will get up to $8 per share, based on whether or not the company's drug Zilretta achieves certain sales milestones and other experimental treatments get regulatory clearances. (Reporting by Dania Nadeem in Bengaluru; Editing by Saumyadeb Chakrabarty)