Constipation may be defined as the passage of excessively dry stool, infrequent stool, or stool of insufficient size.24,25 It involves the subjective sensations of incomplete emptying of the rectum, bloating, flatulence, lower abdominal discomfort, anorexia, malaise, headache, weakness, and giddiness. Constipation may be of brief duration (e.g., when one's living habits and diet change abruptly) or it may be a lifelong problem (e.g., as seen in congenital aganglionosis of the colon).
Major causes of constipation include functional abnormalities, colonic disease, rectal problems, neurological diseases and metabolic conditions.24,25 In addition, the administration of many drugs (anticholinergic drugs found in many of the over-the counter medications, antiparkinsonian drugs with anticholinergic properties, antihistamines, neuroleptics, antidepressants, anticonvulsants, analgesics, ganglionic blocking agents, antacids, and opioids) may lead to constipation.24,25
Osmotic agents such as docusate or polyethylene glycol 3350 soften stool by increasing the amount of water the stool absorbs and make it easier to pass.2,3,24,25 It is of note that opioid analgesics, by binding μ-receptors in GI tract, increase the tone of the anterior portion of the stomach, decrease gastric motility, and cause constipation. The risk may be minimized by increasing fluid and dietary fiber intake. Constipation is dose related and patients do not develop tolerance.