Irritable bowel syndrome treatment aims to alleviate predominant symptoms, such as diarrhea, constipation, or abdominal cramping (Lee 2012).
Bulking agents (ie, dietary fiber) are frequently used to treat both subtypes of IBS. Insoluble fiber facilitates defecation by reducing transit time, or the time it takes for the remains of ingested food to be excreted. While defecation generally alleviates IBS symptoms, a comprehensive review found conflicting effects of bulking agents on IBS severity (Trinkley 2011; Ruepert 2011). A potential side effect of fiber supplements is bloating (Mayer 2008), which can exacerbate certain IBS types who have difficulty evacuating their bowels.
Laxatives and stool softeners are commonly used to treat IBS-C (Trinkley 2011; Mayer 2008). These treatments typically provide rapid relief, but are not recommended for long-term use as they can cause electrolyte imbalances by enhancing the excretion of fluids (Roerig 2010). The most common laxatives work by osmosis, that is, they draw fluid into the intestine producing softer stools that are easier to pass. Polyethylene glycol (MiraLAX®) is one of the most studied laxatives; it has been shown to be superior to lactulose (another osmotic laxative) (Attar 1999). Lubiprostone (Amitiza®) is a prostaglandin E1 analog that draws fluid into the intestine by directly acting on the ClC2 chloride receptor. Lubiprostone is indicated for IBS-C in the United States (Trinkley 2011; Barish 2010). Lubiprostone acts quickly to facilitate defecation, relieve discomfort, and resolve abdominal pain (Lacy 2008; Ambizas 2007).
Antispasmodics relax the smooth muscle of the lower GI tract and may be helpful in IBS, especially for abdominal pain; although more data from high quality randomized controlled trials are needed to thoroughly assess their effectiveness (Ruepert 2011; Trinkley 2011; Mayer 2008). In studies conducted in Europe, alverine (Spasmonyl®), which blocks signaling through a specific serotonin receptor called 5-HT1a, was effective at relieving abdominal pain and discomfort in IBS patients when combined with the oral anti-foaming agent simethicone (Gas-X®) (Wittmann 2010). However, alverine was shown to be ineffective when used alone (Mitchell 2002). Antagonists of either muscarinic acetylcholine or 5-HT1a receptors exert direct antispasmodic effects, whereas simethicone reduces gas/flatulence and is not an antispasmodic (Wittmann 2010). Propantheline (Probanthine™) is an anticholinergic antispasmodic medication used to treat IBS (PubMed Health 2011).
Antidepressants are another class of therapeutic agents that can be used in IBS treatment (Trinkley 2011). They do not address the underlying condition, but instead reduce feelings of discomfort. These drugs have demonstrated a modest degree of success (Ruepert 2011). The selective serotonin reuptake inhibitor (SSRI) paroxetine (Paxil®) has shown some benefits (Masand 2009), although results with another SSRI, citalopram (Celexa®), suggest that efficacy might be limited to IBS sufferers who are also clinically depressed (Ladabaum 2010). The dual serotonin norepinephrine reuptake inhibitor (SNRI) duloxetine (Cymbalta®), on the other hand, is efficacious in non-depressed IBS patients, but is typically limited to IBS-D since constipation is a potential side effect (Brennan 2009). Tricyclic antidepressant drugs like amitriptyline inhibit peristalsis and can markedly worsen constipation-predominant IBS.
Alosetron (Lotronex®), which blocks an intestinal serotonin receptor called the 5-HT3 receptor, is used to treat IBS-D (Cremonini 2012; Spiller 2007). One randomized clinical trial in women with severe IBS-D showed significant beneficial effects of alosetron vs. placebo, whereby every measured aspect of quality of life improved (eg, emotional, mental health, sleep, energy, etc.) and workplace productivity increased (Cremonini 2012). However, alosetron may cause significant side effects including severe constipation and loss of blood flow to the colon (PubMed Health 2010; Gallo-Torres 2006). Alosetron is indicated for use in women with severe IBS-Diarrhea who have not responded to other therapies (Mayer 2008) and not IBS of the constipation type.
Other treatment considerations
Small intestinal bacterial overgrowth
Evidence suggests that small intestinal bacterial overgrowth (SIBO) may contribute to IBS symptoms in some patients (Yamini 2010; Lee 2006). The gold standard for diagnosing SIBO is microbial investigation of fluids collected from the small intestine. Other non-invasive testing such as hydrogen and methane breath tests are more commonly used. Antibiotics are a mainstay in SIBO therapy however, probiotics (see below) are becoming an increasingly appreciated option (Quigley 2006; Bures 2010).
Premenopausal women often experience IBS symptom exacerbation around menstruation, which may be related to fluctuations in sex hormone levels (Jane 2011; Heitkemper 2009). Using blood testing to assess hormone levels and, if necessary, working with an experienced, integrative physician to appropriately balance hormone levels may represent a potential solution, though studies have yet to test this hypothesis.