Kythera Biopharmaceuticals, Inc. will be acquired by Allergan plc in a $2.1 billion buyout announced Wednesday.

The Westlake Village biotech owns Kybella, an injectable treatment that dissolves fat. It was approved by the Food and Drug Administration in April to treat chin fat.

Kybella fits well with Allergan’s product line, which includes BoTox, the injectable wrinkle treatment. Both drugs require a doctor’s prescription but usually don’t qualify for payment by insurance companies.

Allergan was known as Actavis Plc until it bought Irvine-based Allergan Inc. for $72.5 billion earlier this year and took the Allergan name. Allergan’s U.S. operations are based in Parsippany, N.J., while the parent company is based in Ireland.

“Allergan’s world-class medical aesthetics, global footprint, history and commitment to developing leading aesthetic products makes them ideally suited to realize the maximum commercial potential of Kybella,” Keith Leonard, chief executive of Kythera, said in a statement.

The buyout will price Kythera shares at $75, a 23.5 percent premium over Tuesday’s closing price. Allergan will pay Kythera shareholders with 80 percent cash and 20 percent in Allergan shares.

In mid-day trading, Kythera shares were up $13.42 or 22 percent, to $74.14 on the Nasdaq.