Irritable bowel syndrome (IBS) is a disease you may already have heard of, but with April designated as IBS awareness month, it is worth revisiting this under-diagnosed and under-treated disease. Although the symptoms of various IBS presentations are fairly burdensome, a diagnosis of elimination is still required, with physicians ruling out other possibilities before making an official diagnosis of IBS. To add to this confusion, there are three major forms of IBS; constipation-predominant (IBS-C), diarrhea-predominant (IBS-D), and a mixed presentation (IBS-M), and these contrary symptoms can make it difficult to arrive at a determination of IBS, especially for physicians who are less familiar with the variable symptomology of this condition.

As a consequence of low awareness, high unmet need, and difficulty making a final diagnosis, all forms of IBS are currently under-diagnosed and under-treated by a fairly large margin, with less than a quarter of the total U.S. prevalent population diagnosed; of these, only 55% were drug-treated in 2017. DRG’s epidemiology insights report that only about 20% of the total IBS population is the constipation-predominant subtype, and if we assume that the drug-treatment and diagnosis rates are the same across all populations, then only about 700,000 of the total 5.2 million IBS-C patients received drug treatment in the United States in 2017. These epidemiological numbers alone highlight the significant need for increased awareness and the opportunity to increase market share by improving the diagnosis and drug-treatment rates, but for pharmaceutical manufacturers to capitalize on this opportunity, it will also be important to understand how physicians prioritize various factors when selecting among treatments.

In addition to low awareness, another factor limiting the growth of this market is the lack of effective prescription therapies. Currently, only three drugs have achieved a label indication for IBS-C in the United States; lubiprostone was approved in 2006 for chronic idiopathic constipation (CIC), a separate but related condition that presents with constipation but without the abdominal pain present in IBS-C, and achieved the IBS-C label in 2008. Similarly, plecanatide was originally approved for CIC in 2016, with the label extension for IBS-C granted early in 2018. In contrast, linaclotide was approved for IBS-C in 2012 and achieved the CIC label as an extension in 2017. These therapies were all approved based on their combined responder rate, where patients were evaluated for an increase in complete spontaneous bowel movements (CSBMs) and a decrease in abdominal pain or discomfort; no therapy to date has surpassed a combined responder rate of 35%, leaving a lot of room for improvement. Although additional therapies are used to treat IBS-C, none have a label indication for this disease, and they are either readily available OTC therapies or prescribed off-label and approved for CIC or opioid-induced constipation (OIC), a condition with similar symptoms but with a clear iatrogenic cause.

Linaclotide’s successful achievement of IBS-C as the initial label appears to have paid off quite well in the market, with surveyed U.S. physicians reporting a higher level of satisfaction for linaclotide than any of its IBS-C approved competitors, according to DRG’s recently published IBS-C Unmet Need report. Interestingly, only about 30% of linaclotide prescriptions are coded for IBS-C in Syneos Health’s claims database, with the remainder of prescriptions written for unspecified constipation, but the portion of this drug’s sales attributable to IBS-C grew by 100% between 2015 and 2016. Lubiprostone’s IBS-C attributable sales performed slightly worse, growing by about 66% from 2015 to 2016, but this growth remains impressive when compared to more mature disease markets. With its later launch, sales trends are not yet available for plecanatide, but in combination, these drugs reached almost $400 million in IBS-C sales in 2016.


Considering the low diagnosis and drug-treatment rates, IBS-C therapies could continue to experience growth even without pursuing competitive strategies, by working to improve awareness of this disease. If the assumption holds that the diagnosis and drug-treatment rates for the combined IBS population can be applied to the IBS-C subtype, only 10% of these patients are currently receiving prescription therapy for this condition. Increasing the diagnosis rate is likely to have the biggest payoff, with about three-quarters of the total IBS prevalent population remaining undiagnosed in 2018, and if growth trends continue for currently available IBS-C drugs, this market could easily surpass $1 billion by 2020.

In addition to the large growth potential, the level of unmet need in IBS-C makes this market particularly attractive to developers. Only one drug, tenapanor, is currently in late-stage clinical trials for this disease, and available drugs often fail to return patients entirely to normal bowel function. Consequently, any drug able to deliver even marginal improvements over existing therapies has the potential to steal market share away from its competitors, and a new therapy with superior results could also generate publicity to help raise physician and patient awareness, expanding the market even further. With only three drugs launched in the United States, and with even these limited options helping drive large year-over-year sales growth, the IBS-C market is ripe for development and could deliver a robust payoff to any manufacturer able to secure approval.

DRG recently explored the unmet need in IBS-C through a survey of 90 U.S. and European gastroenterologists. For more details on this research, please contact


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