The battle for what is projected to be a $2.3 billion market by 2025 is heating up between two pharmaceutical companies – Valeant, maker of Xifaxan (rifaximin), and Allegan, which produces Viberzi (eluxadoline).
Prominent Deutsche Bank analysts are predicting that Xifaxan will ultimately come out on top, based on a survey of 25 primary care physicians who regularly write prescriptions for patients suffering from diarrhea caused by irritable bowel syndrome (IBS-D), the primary indication for both medications.
Xifaxan and Allergan both won FDA approval for the treatment of IBS-D in May 2015, although the latter was unable to bring Viberzi to market until the following December because the product had to undergo review by the Drug Enforcement Agency. Ultimately, Viberzi was classified as a Schedule IV drug (substances with a low potential for abuse and risk of dependence).
Prior to the release of Xifaxan and Allergan, the only medication approved for treating IBS-D was Lotronex (alosetron), which was indicated only for women patients. Lotronex was taken off the market in 2000 because of rare, but potentially fatal side effects. The medication was reinstated two years later with restriction by the FDA, despite opposition from patient advocacy groups.
Although Xifaxan and Viberzi are used to treat the same condition, their respective mechanisms of action are quite different. Xifaxan is essentially an antibiotic, targeting gut flora – specifically, the harmful bacteria that is believed to cause IBS. This relieves abdominal pain and affects the consistency of the patient's stools. Common side effects include nausea and an increase in liver enzymes, which if not treated, can lead to hepatitis and cirrhosis. A course of treatment with Xifaxan lasts two weeks, relieving patient symptoms for up to six months.
Viberzi is an opioid receptor inhibitor. This medication works by preventing the opioid receptors in the intestines from functioning, thus relieving the pain associated with IBS-D and slowing down intestinal movement. Common side effects include nausea and vomiting, respiratory issues, dizziness, flatulence and fatigue.
In patients who have had their gall bladder removed, however, the consequences can be far more serious. The FDA has reported more than 120 cases who have wound up with severe pancreatic inflammation as a result of taking Viberzi, nearly half of whom had undergone a cholecystectomy (gall bladder removal). So far, two patient deaths have been attributed to Viberzi.
One thing the two medications have in common is an exorbitant price tag. In the U.S., a monthly supply of Xifaxan costs over $1800 per month. The average cost to U.S. patients for Viberzi averages nearly $1300 for 60 tablets.
Because Allergan allegedly failed to warn cholecystectomy patients and their doctors about the potentially fatal side effects of Viberzi, law firms across the country have begun investigations in anticipation of litigation against the manufacturer.