The deal price is a 46% premium to the Waltham, Mass., biopharma's $9.40 closing price on Wednesday.
Amag shares at last check rose 45% to $13.60. They touched a 52-week low of $4.41 on March 18. A bit more than two years ago they were trading above $25.
Including debt, the deal's enterprise value is $647 million.
Covis, based in Luxembourg and operating from Zug, Switzerland, is backed by the New York private-equity firm Apollo Global Management. (APO) - Get Report Covis is a specialty pharmaceutical producer, focused, its website says, on respiratory and allergy, cardiovascular, gastroenterology and more.
Amag focuses on what it calls "underrecognized health conditions." The website describes drugs to, for examples, reduce the risk of preterm birth and treat iron-deficiency anemia in adults.
"Amag's category-leading treatments are strong strategic complements to our existing therapeutic portfolio," Covis Chief Executive Michael Porter said in a statement.
Around this time last year, Amag agreed to add two directors proposed by activist investment group Caligan Partners after the hedge fund, which owned a 10.3% stake in the Amag, pressured the company to conduct a strategic review.
Early on in 2020 Amag had undertaken a strategic review of its businesses and sold its women's-health assets.
Both boards have approved the Covis deal terms.
The purchase is subject to conditions including antitrust clearance and Amag holders tendering at least a majority of the shares. Covis has arranged financing for the transaction, with cash on hand plus debt and equity funding. The companies hope to close the purchase in November.