AstraZeneca is planning to spend about $260 million on Omthera Pharmaceuticals Inc., a specialty drug developer with a potential treatment for patients who have high levels of fats called triglycerides in their blood.

AstraZeneca says it will pay $12.70 for each share of Omthera, which priced an initial public offering last month at $8. AstraZeneca’s price represents an 87 percent premium compared to Friday’s closing price of $6.77.

Its shares rose 89 percent to $12.80 in premarket trading Tuesday.

The deal totals about $323 million when counting Omthera’s cash balances. Omthera shareholders also could receive additional payments totaling about $120 million if the potential treatment called Epanova reaches development milestones.

Omthera has completed late-stage testing on Epanova, a fish oil-based treatment. It plans to submit the drug to U.S. regulators for approval by the middle of this year.