Other uses—Because it inhibits pancreatic secretion, octreotide may be of value in patients with pancreatic fistula. The role of octreotide in the treatment of pituitary tumors (eg, acromegaly) is discussed in Chapter 37. Octreotide is sometimes used in gastrointestinal bleeding (see below).
Impaired pancreatic secretion may cause steatorrhea, which can lead to fat-soluble vitamin deficiency. Alterations in gastrointestinal motility cause nausea, abdominal pain, flatulence, and diarrhea. Because of inhibition of gallbladder contractility and alterations in fat absorption, long-term use of octreotide can cause formation of sludge or gallstones in over 50% of patients, which rarely results in the development of acute cholecystitis. Because octreotide alters the balance among insulin, glucagon, and growth hormone, hyperglycemia or, less frequently, hypoglycemia (usually mild) can occur. Prolonged treatment with octreotide may result in hypothyroidism. Octreotide also can cause bradycardia.
IBS is an idiopathic chronic, relapsing disorder characterized by abdominal discomfort (pain, bloating, distention, or cramps) in association with alterations in bowel habits (diarrhea, constipation, or both). With episodes of abdominal pain or discomfort, patients note a change in the frequency or consistency of their bowel movements.
Pharmacologic therapies for IBS are directed at relieving abdominal pain and discomfort and improving bowel function. For patients with predominant diarrhea, antidiarrheal agents, especially loperamide, are helpful in reducing stool frequency and fecal urgency. For patients with predominant constipation, fiber supplements may lead to softening of stools and reduced straining; however, increased gas production may exacerbate bloating and abdominal discomfort. Consequently, osmotic laxatives, especially milk of magnesia, are commonly used to soften stools and promote increased stool frequency.
For chronic abdominal pain, low doses of tricyclic antidepressants (eg, amitriptyline or desipramine, 10–50 mg/d) appear to be helpful (see Chapter 30). At these doses, these agents have no effect on mood but may alter central processing of visceral afferent information. The anticholinergic properties of these agents also may have effects on gastrointestinal motility and secretion, reducing stool frequency and liquidity. Finally, tricyclic antidepressants may alter receptors for enteric neurotransmitters such as serotonin, affecting visceral afferent sensation.
Several other agents are available that are specifically intended for the treatment of IBS.
Some agents are promoted as providing relief of abdominal pain or discomfort through antispasmodic actions. However, small or large bowel spasm has not been found to be an important cause of symptoms in patients with IBS. Antispasmodics work primarily through anticholinergic activities. Commonly used medications in this class include dicyclomine and hyoscyamine (see Chapter 8). These drugs inhibit muscarinic cholinergic receptors in the enteric plexus and on smooth muscle. The efficacy of antispasmodics for relief of abdominal symptoms has never been convincingly demonstrated. At low doses, they have minimal autonomic effects.
However, at higher doses they exhibit significant additional anticholinergic effects, including dry mouth, visual disturbances, urinary retention, and constipation. For these reasons, antispasmodics are infrequently used.