Amitiza, a new type of laxative launched in Japan

A new type of laxative, lubiprostone (Amitiza®), appeared this November in the Japanese market. It is the first medicine that meets the indication of chronic constipation, characterized by less development of tolerance. Amitiza® can be safely used for a long period. It may also be administered to patients with reduced renal function who cannot use magnesium oxide, which might raise serum magnesium ion levels enough to cause fatal arrhythmia. Speaking of laxatives, many people would have an image of “inexpensive prices.” But a capsule of Amitiza® costs 156.5 yen, much more expensive than existing laxatives. Moreover, it needs to be taken twice a day.

As you can see, the structural formula shows that it is a kind of prostaglandins. Prostaglandin preparations remind us that they are usually expensive. This is true.

Lubiprostone is not metabolized in the small intestine and combines with a type 2 chloride channel (ClC-2) on the apical aspect of gastrointestinal epithelial cells, opening the channel. Chloride ions are pumped out of the cell, which produces a chloride-rich fluid secretion. The secretion softens the stool, increases motility and promotes spontaneous bowel movements. This mechanism is similar to that of a traditional laxative magnesium oxide, which increases the osmotic pressure in the intestine and softens the stool.

The Health, Labor and Welfare Ministry approved manufacturing and distribution of Amitiza® indicated for chronic constipation (excluding constipation caused by structural disease) this July. It is the first laxative that received approval to treat “chronic” constipation, developed by SUCAMPO Pharmaceuticals in Maryland, the U.S. and domestically distributed by ABBOTT JAPAN Co., Ltd. It was released November 22 following the National Health Insurance price listing.

Distribution of the medicine was approved for patients with chronic idiopathic constipation in the U.S. in 2006 and in Switzerland in 2009. Besides, it received approval to treat chronic irritable bowel syndrome in the U.S. in 2008. The medicine is now under application for an indication extended to opioid-induced constipation.