Describe the mechanism of action of bulk-forming laxatives (fiber), e.g., psyllium husks (Flohsamenschalen)
Bulk-forming laxatives are indigestible, not systemically absorbed.
Soluble fibers increase water absorption in the intestinal lumen → stretching of the bowel wall → stimulation of peristalsis
Describe the mechanism of action of osmotic laxatives, e.g., disaccharides such as lactulose.
Increase of osmotic pressure draws water into the intestinal lumen → stimulation of intestinal motility (peristalsis)
List adverse effects of osmotic laxatives.
Magnesium salts: electrolyte abnormalities
Describe the mechanism of action of stimulant laxatives (secretory laxatives), such as Senna.
Stimulation of epithelial cell secretion of electrolytes into the colonic lumen →
↑ Secretion of fluid into the colon (with bisacodyl, this secretory activity is nitric oxide-mediated)
Myenteric neuronal depolarization → colon contractions (peristalsis)
Stimulant laxative; primary active cathartic principles are the stereoisomeric glucosides, sennosides A and B.
Commonly thought that the stimulant laxatives induce defecation by stimulating propulsive peristaltic activity of the intestine through local irritation of the mucosa or through a more selective action on the intramural nerve plexus of intestinal smooth muscle, thus increasing motility.
More recent evidence shows that stimulant laxatives alter fluid and electrolyte absorption, producing net intestinal fluid accumulation and laxation.
Increases concentrations of cyclic 3′,5′-adenosine monophosphate (cAMP) in colonic mucosal cells and may alter the permeability of these cells and mediate active ion secretion, producing net fluid accumulation and laxative action.
Mainly promotes evacuation of the colon.
Describe adverse effects of Senna.
Diarrhea, which may result in severe water and potassium loss
Melanosis coli (senna)
List contraindications for Senna.
Acute abdominal pain, nausea, vomiting, or other symptoms of appendicitis or undiagnosed abdominal pain.