NEW YORK — Activist investor Starboard Value said Monday that it bought a 4.6 percent stake in Perrigo and pushed the Irish drugmaker to shake up its business.

In a letter to Perrigo’s management, Starboard said that the company’s performance has been “poor” and that it needs to make changes to create value for shareholders. Starboard said Perrigo’s plans last year to improve the company on its own after it rejected a takeover bid from rival Mylan NV did not pan out.

Perrigo said in a statement that it is reviewing Starboard’s letter “carefully.”

Dublin-based Perrigo makes infant formula and over-the-counter medications for store brands.

Shares of Perrigo Co. are down more than 46 percent in the last year. They rose $5.77, or 7.6 percent, to $95.48 in afternoon trading Monday.