What is the recommended treatment approach for an adult with irritable bowel syndrome with constipation (IBS-C) and no comorbidities?

Treatment for IBS-C

Start with linaclotide 290 mcg once daily as first-line pharmacological therapy for IBS-C, as it is the only treatment with strong evidence showing improvement in both abdominal pain and bowel movements. 1

Initial Management Approach

Before initiating pharmacological therapy, establish a positive diagnosis without extensive testing if the patient is under 45 years old and lacks alarm features (unintentional weight loss, blood in stool, fever, anemia, family history of colon cancer or inflammatory bowel disease). 2 Explain to the patient that IBS-C is a disorder of gut-brain interaction with a benign but relapsing/remitting course to set realistic expectations. 2

Lifestyle and Dietary Modifications (Implement Concurrently)

• Prescribe regular physical activity to all IBS-C patients, as exercise provides significant benefits for symptom management. 2

• Start soluble fiber supplementation with ispaghula/psyllium at 3-4 g/day, gradually increasing to avoid bloating. 2, 3 This is critical—avoid insoluble fiber (wheat bran) as it worsens symptoms, particularly bloating. 2

• Establish regular time for defecation and ensure adequate sleep hygiene. 2

• For patients with persistent symptoms despite standard dietary advice, implement a supervised low FODMAP diet delivered in three phases: restriction, reintroduction, and personalization. 2 This requires referral to a gastroenterology dietitian. 2

First-Line Pharmacological Treatment

Linaclotide 290 mcg once daily is the recommended first-line pharmacological agent based on high-quality evidence from two large randomized controlled trials showing modest but significant improvement in both abdominal pain and complete spontaneous bowel movements (the FDA-defined response). 1, 4 In these trials, 12-13% of patients achieved combined response (abdominal pain reduction ≥30% and ≥3 CSBMs with ≥1 increase from baseline) compared to 3-5% with placebo. 4

Common pitfall: Diarrhea leading to treatment discontinuation occurs in a small percentage of patients, so counsel patients about this risk upfront. 1 Patients who place high value on avoiding diarrhea or higher out-of-pocket expenses may prefer alternate treatments. 1

Second-Line Pharmacological Treatment

If linaclotide is ineffective, not tolerated, or cost-prohibitive, use lubiprostone as second-line therapy. 1 Two 12-week RCTs showed small improvement in global IBS symptoms with few adverse effects, though the evidence quality is moderate rather than high. 1

Treatment for Abdominal Pain (If Predominant Symptom)

• Use antispasmodics with anticholinergic properties (dicyclomine) as first-line therapy for abdominal pain, particularly when symptoms are meal-related. 2

• Peppermint oil may be used as an alternative antispasmodic, though evidence is more limited. 2, 3

• For refractory abdominal pain despite secretagogues and antispasmodics, initiate tricyclic antidepressants (TCAs) such as amitriptyline starting at 10 mg once daily, titrating slowly to a maximum of 30-50 mg once daily. 2 TCAs show modest improvement in global relief and abdominal pain, though overall evidence quality is low. 1 Critical caveat: Use TCAs with caution in patients at risk for QT interval prolongation. 1

• Do not use selective serotonin reuptake inhibitors (SSRIs) for IBS-C unless a co-occurring mood disorder is present, as pooled data from 5 RCTs showed no improvement in global relief or abdominal pain symptoms. 1

Psychological Therapies for Refractory Cases

Refer for IBS-specific cognitive behavioral therapy or gut-directed hypnotherapy when symptoms persist despite pharmacological treatment for 12 months. 2 These brain-gut behavior therapies are specifically designed for IBS and differ from psychological therapies targeting depression and anxiety alone. 2 Earlier referral is appropriate if the patient has moderate to severe symptoms, accepts that symptoms relate to gut-brain dysregulation, and has time to devote to learning new coping strategies. 2

Treatment Monitoring and Adjustment

• Review treatment efficacy after 3 months and discontinue ineffective medications. 2

• Recognize that symptoms may relapse and remit over time, requiring periodic adjustment of treatment strategy. 2

• Do not use osmotic laxatives (polyethylene glycol) or stimulant laxatives (senna) as primary therapy for IBS-C, as evidence for efficacy in IBS-C specifically is very limited despite effectiveness for chronic idiopathic constipation. 1

Multidisciplinary Referral Criteria

• Refer to a gastroenterology dietitian if the patient consumes considerable intake of foods that trigger IBS symptoms, shows dietary deficits or nutritional deficiency, shows recent unintended weight loss, or requests dietary modification advice. 2

• Refer to a gastropsychologist if IBS symptoms or their impact are moderate to severe, the patient accepts that symptoms are related to gut-brain dysregulation, and has time to devote to learning new coping strategies. 2