The studies, which are published in the New England Journal of Medicine, found that linoclotide relieved chronic constipation in up to 21% of patients, compared to as many as 6% who were helped on a placebo.
As many as one in five Americans suffer from chronic constipation, meaning that they have fewer than three bowel movements a week for at least three months. The condition is most common in women, the elderly, and people who suffer from irritable bowel syndrome.
There's currently one prescription drug, Amitiza, that's widely used for treating chronic constipation.
A host of other over-the-counter remedies haven't been well studied in patients for whom constipation has become a long-term problem.
Study researcher Anthony J. Lembo, MD, a gastroenterologist at Beth Israel Deaconess Medical Center in Boston, says linoclotide is unique because it stimulates cells in the lining of the bowel to produce secretions that help draw more fluid into the gut. The fluid helps to soften stool and speed its passage.
"It won't help everybody, of course. Not all patients have their symptoms relieved," Lembo tells WebMD. "There are a lot of different causes for constipation."
Investigating a New Medication for Chronic Constipation
To test the drug, researchers recruited more than 1,200 adults in the U.S. and Canada who had histories of chronic constipation along with symptoms like straining, lumpy or hard stools, and a feeling of incomplete evacuation.
There were roughly 600 patients in each study.
In both trials, people were randomly assigned to one of three groups: those on a lower daily dose of linoclotide, those on a higher dose, and those who were unknowingly taking a placebo.
They were asked to take their capsules 30 minutes before breakfast each day for 12 weeks.
Researchers considered the patients successfully treated if they'd had at least three complete bowel movements each week plus at least one more bowel movement each week than they had averaged going into the study for nine out of 12 weeks.
In the first study, 21% of the patients on the low dose of the drug and 19% of patients on the high dose of the drug achieved that goal, compared to 3% who were taking the placebo.
In the second study, 16% on the low dose and 21% on the higher dose met that target, compared to 6% who were taking the placebo.
Stated another way, about six to 10 people would need to take the drug for one person to see a benefit.
The most commonly reported side effect was diarrhea, which affected 14% to 16% of patients on the high and low doses and about 5% who were taking the placebo.
Researchers said most of the diarrhea reported in the study occurred early on and went away as people got used to the medication.
But for about 5% of people, it was a side effect that was bothersome enough to cause them to drop out of the study.
The studies were sponsored by Ironwood Pharmaceuticals and Forest Research Institute, the companies that are developing the drug.
Experts said the studies were welcome news since few therapies have been proven to be safe or effective for a condition that can make people miserable.
"If you're constipated, you become uncomfortable," says Anthony Starpoli, MD, a gastroenterologist at Lenox Hill Hospital in New York City. "You have bloating, distention, all of these sorts of things."
"I think this is great, and the safety profile is terrific from everything that they're showing," says Starpoli, who was not involved in the research. "Of course, once this is implemented in clinical practice, sometimes the picture changes."
The drug isn't yet available to patients. The drug's manufacturer has applied for FDA approval. A decision isn't expected until next year.
"Linoclotide is actually quite promising," says Lawrence Leung, MBBChir, an assistant professor in the department of family medicine at Queens University in Kingston, Ontario, Canada.
"My concern is that it could be pretty expensive," says Leung, who recently reviewed the evidence behind treatments for chronic constipation but was not involved in the current research.
Because the elderly suffer from chronic constipation in disproportionate numbers, he thinks it will fall on public programs like Medicare to pay for the drug.
"The cost will be a concern, and I'm not sure whether governments will like to bear the cost for a drug that should be used every day," he says.
Advice to Patients
Until more treatments are available, experts say lifestyle changes are the place to start.
"While this is a very promising agent, we have to remember that we should be drinking 6-8 glasses of free fluid a day," Starpoli says, meaning non-dehydrating beverages. Coffee, tea, and alcohol, which can cause the body to lose fluid, don't count.
He also encourages his patients to get more soluble fiber, the kind that gets gummy in water. Good sources of soluble fiber include oatmeal, okra, and beans.