Scientists have developed a new drug capsule that stays in the stomach for up to two weeks after being swallowed, gradually releasing its payload.

The capsule, developed by researchers in the United States, could be a powerful weapon in fighting malaria, HIV and other diseases where successful treatment depends on repeated doses of medicine.

In a study published in the Science Translational Medicine journal on Wednesday, the researchers used the new capsule to deliver an anti-parasitic drug called ivermectin, which they believe could help fight malaria.

The long-acting pill technology could also have a range of other applications, the scientists said - from use in treating Alzheimer's disease and mental illnesses to HIV and tuberculosis.

Although long-acting drug delivery systems already exist, they are either injectable or implantable, or involve an invasive procedure and are not suitable for many situations.

"Until now, oral drugs would almost never last for more than a day," said Robert Langer, a professor at MIT who worked on the study.

"This really opens the door to ultra-long-lasting oral systems ... There are a lot of exciting things this could someday enable."

Drugs taken orally tend to work for a limited time because they pass quickly through the body and are exposed to harsh environments in the stomach and intestines.

Langer said he and his team have been working for several years to overcome this problem, initially focusing on malaria and ivermectin, which kills any mosquito that bites someone who is taking the drug.

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The new long-acting pill has a star-shaped structure with six arms that can be folded inwards and are encased in a smooth capsule. Drug doses are loaded into the arms, and each arm is attached to a core by a linker that is designed eventually to break down.

After the capsule is swallowed, acid in the stomach dissolves the outer capsule layer, allowing the arms to unfold. Once the star expands it stays in the stomach. It is big enough to resist the forces that would normally push something down the digestive tract, but too small to cause a blockage.

"When the star opens up inside the stomach, it stays inside the stomach for the duration that you need," said Tyler Grant, another researcher on the project.

In tests in pigs, the researchers found that drug doses were gradually released over two weeks, and the linkers that join the arms to the core then dissolved, allowing the arms to break off and pass through the digestive system.

The researchers ran mathematical models to analyze the potential impact of the long-acting capsule with ivermectin.

Models suggest that if the capsules were used to deliver ivermectin along with antimalaria treatments to 70 percent of a population, malaria transmission could be cut by as much as it would have been if 90 percent had been treated with antimalaria treatments alone.

The team is working on developing similar capsules to deliver drugs against other tropical diseases, as well as HIV and tuberculosis.