Washington - The United States Food and Drug Administration has approved a new prescription drug called Amitiza to treat adults with chronic constipation, one of the most common disorders among Americans, the agency said on Tuesday.

The drug, made by privately held Sucampo Pharmaceuticals, is the first of a new kind of treatment that works by increasing the amount of fluid in the intestines, officials said.

Japan's Takeda Pharmaceutical will help promote and sell the drug, a type of chloride channel activator.

Amitiza is intended for patients who experience constipation over time with no known cause, and should be taken twice daily with food, the FDA said in a statement.

The capsules aim to relieve constipation, abdominal bloating and discomfort. Side effects can include headache, nausea, diarrhoea and abdominal pain, among others.

Sucampo spokesperson Brad Fackler would not comment on the Bethesda, Maryland-based company's sales projections or terms of the deal with Takeda. He added that about 30 million Americans suffer from constipation each year.

Dozens of over-the-counter laxatives are available on the US market, including fiber-filled products, stool softeners and stimulants. Some types are also abused by users looking to lose or maintain weight.

Unlike most laxatives, which often increase fluid in the stool itself, Fackler said Amitiza helps the stool move through the intestines.

The company is also considering seeking approval in other countries, he added.

Representatives for Takeda referred calls to Sucampo. Earlier on Tuesday, shares of the Japanese drugmaker closed up 1,68 percent in Tokyo.