An Amgen sign is seen at the company's office in South San Francisco, California October 21, 2013.
An Amgen sign is seen at the company's office in South San Francisco, California October 21, 2013. Reuters / Robert Galbraith

U.S. drugmaker Amgen Inc is buying ChemoCentryx Inc for $3.7 billion to gain access to a potential blockbuster treatment for inflammatory disorders.

The buyout will also hand Amgen control of at least two experimental therapies for immune disorders, a field that has come into the spotlight after AstraZeneca's 2020 purchase of Alexion Pharmaceuticals for $39 billion.

Amgen has been facing stiff competition for its top-selling arthritis drug, Enbrel, from newer branded rivals and patents for the therapy are expected to expire in 2029.

The company said on Thursday it would pay $52 in cash for each share of ChemoCentryx, a premium of nearly 116% to the target's last closing price. ChemoCentryx shares surged on the news to trade just $1 shy of the offer price.

"We view Amgen as a logical partner to take the torch from (ChemoCentryx) and continue the launch of Tavneos," said SVB Securities analyst Joseph Schwartz.

Approved late last year to treat patients with a rare form of blood vessel inflammation or vasculitis, Tavneos brought in sales of $5.4 million in the first full quarter of its launch.

Vasculitis is caused by an over-activation of the immune system and can be fatal if not treated. The disease affects about 40,000 people in the United States, with about 4,000 new cases each year, according to ChemoCentryx.

Analysts expect the drug, which is also being tested for other inflammatory conditions, to generate more than $1 billion in sales by 2027, Refinitiv data shows.

ChemoCentryx is also developing a cancer drug.