Irish pharmaceutical-maker Shire PLC is buying biopharmaceutical firm NPS Pharmaceuticals of New Jersey for an estimated $5.2 billion, Shire announced Sunday. Shire offered $46 per share for the rare-disease-focused company, a 51 percent premium on NPS Pharma's mid-December value of $30.47 a share. Prices began rising as rumors of the sale developed.

NPS closed Friday at $41.91 a share.

Fierce Biotech reported Shire was the logical buyer for NPS, following AbbVie's decision not to go through with a merger that would have headquartered the combined company in Dublin. The deal collapsed after the U.S. government changed the rules on tax inversions. The breakup added $1.6 billion to Shire's cash reserves that analysts now estimate at $13 billion.

Sunday's deal gives Shire access to Gattex/Revestive, an injectible drug approved in the United States and Europe for the treatment of short bowel syndrome. NPS also is in the process of registering Natpara/Natpar for treatment of hypoparathyroidism.

“We look forward to accelerating the growth of the NPS Pharma portfolio based on our proven track record of maximizing value from acquired assets and commercial execution. The NPS Pharma organization will be a welcome addition to Shire as we continue to help transform the lives of patients with rare diseases,” Shire CEO Flemming Ornskov said in a press release.

NPS President and CEO Francois Nader said Shire shares NPS Pharma's "commitment to patients with rare diseases. We believe that joining our two companies will drive value for shareholders and ensure we continue to transform the lives of patients with short bowel syndrome, hypoparathyroidism and autosomal dominant hypocalcemia worldwide."

Shire is buying NPS with the help of an $850 million short-term line of credit, in addition to an existing $2.1 billion, five-year revolving credit line. Shire plans to issue new debt to repay the short-term loan, the company said.

The deal is expected to close by April 1.