Table 1.
Pharmacologic Therapies for IBS Primarily Target Single Symptoms
| Drug Category | Examples | Therapeutic Rationale | Primary Target Symptoms | Tolerability Concerns |
|---|---|---|---|---|
| Traditional Therapies | ||||
| Bulking agents[2] | Wheat bran, corn fiber, calcium polycarbophil, psyllium | Accelerate intestinal transit, add fluid to stool mass, and create gel-like matrix in stool | Constipation, diarrhea | May increase intestinal gas, bloating, and abdominal discomfort |
| Osmotic laxatives[137] | Magnesium hydroxide, sodium phosphate, lactulose, sorbitol solution | Poorly absorbed ions or sugars that cause an influx of fluid and electrolytes into the intestine | Constipation | Diarrhea, dehydration, electrolyte disorders |
| Stimulant laxatives[137] | Senna, bisacodyl, castor oil, aloe | Reduce water and electrolyte absorption by stimulating colonic neurons and irritating the colonic mucosa | Constipation | Dehydration, electrolyte disturbances, significant cramping, and diarrhea. Should be avoided |
| Antidiarrheal agents[2] | Loperamide | Delay intestinal transit and may enhance resting internal anal sphincter tone | Diarrhea | May cause constipation: should not be used in patients with IBS-C; use with caution in patients with alternating IBS symptoms |
| Antispasmodic agents[2] | Hyoscyamine, dicyclomine | Anticholinergic effects and decreased spontaneous activity of intestinal smooth muscle | Diarrhea, abdominal pain | Anticholinergic adverse effects at high doses (including urinary retention and constipation). Use with caution in patients with IBS-C |
| Decreased fluid and electrolyte secretion | ||||
| Antidepressants[2,138] | Desipramine, amitriptyline, trimipramine, doxepin, paroxetine, fluoxetine | Decreased gut sensitivity, decreasing experience of abdominal pain | Pain | Constipation, dry mouth, and dizziness are common adverse effects of TCAs |
| Antianxiety and antidepressant effects | Diarrhea, nausea, nervousness, and fatigue are common adverse effects of SSRIs | |||
| Multiple-Symptom Relief | ||||
| 5-HT3 receptor antagonists (methylimidazole analogs)[102] | Alosetron | Reduce visceral sensitivity and colonic transit | Abdominal pain, diarrhea, urgency | Alosetron: Black box warning regarding serious consequences of constipation; ischemic colitis (reported during clinical trials and in postmarketing surveillance) |
| 5-HT4 receptor agonists[111] (aminoguanidine indoles) | Tegaserod | Reduce visceral sensitivity and increase GI transit and intestinal secretion | Abdominal pain/discomfort, bloating, constipation | Diarrhea, ischemic colitis (reported in postmarketing surveillance) |
IBS = irritable bowel syndrome; IBS-C = IBS with constipation; TCA = tricyclic antidepressant; SSRI = selective serotonin reuptake inhibitor.