Gastrointestinal Medications




FIBER: Fiber supplementation can improve symptoms in patients with constipation. Cereal fibers have cell walls that rest digestion and retain water within their cellular structures. Fiber found in citrus fruits and legumes stimulates the growth of colonic flora, thereby increasing fecal mass. Recommended amount of fiber is 20-35 g/day.

PROS: Low cost, easy to use, safe.
CONS: Bloating, distension, flatulence.

BULK-FORMING LAXATIVES: Psyllium Seed (METAMUCIL), Methylcellulose (CITRUCEL), Calcium Polycarbophil (FIBERCON) and Wheat Dextrin (BENEFIBER). These exert their laxative effect by absorbing water and increasing fecal mass. They are effective at increasing the frequency and softening the consistency of stool.

PROS: Increases frequency, softens consistency.
CONS: Abdominal cramps, intestinal obstruction.

SURFACTANTS: Docusate Sodium (COLACE). Intended to lower the surface tension of stool, thereby allowing water to more easily enter the stool.

PROS: Few side effects.
CONS: Less effective than other laxatives.

OSMOTIC AGENTS: Polyethylene Glycol, poorly absorbed or nonabsorbable sugars, and saline laxatives cause intestinal water secretion and increase stool frequency. Polyethylene Glycol (PEG) can come as an electrolyte solution (GOLYTELY) or powdered preparation (MIRALAX). Synthetic disaccharides such as Lactulose (ENULOSE) are not metabolized by intestinal enzymes and cause water and electrolytes to remain within the lumen due to the osmotic effect of the undigested sugar. Saline laxatives are poorly absorbed and act as hyperosmolar solutions.

Polyethylene Glycol, Electrolyte Solution (GOLYTELY)
PROS: Cause minimal volume shift or electrolyte abnormalities.
CONS: Large volume is difficult for some patients.
DOSE: 240 mL (8 oz) every 10 minutes until 4 L are consumed (bowel prep).

Polyethylene Glycol, Powdered Preparation (MIRALAX)
PROS: Cause minimal volume shift or electrolyte abnormalities.
CONS: Large volume is difficult for some patients.
DOSE: 17 g of powder dissolved in 8 oz of water once daily (constipation).
DOSE: 1.5 g/kg/day for 4 days (bowel prep).

Lactulose (ENULOSE)
PROS: Improves stool frequency and consistency.
CONS: Requires 24-48 hours to achieve effect. Abdominal bloating, flatulence.
DOSE: 10 to 20 g daily (15 to 30 mL or 1 to 2 packets daily) (constipation).
NOTE: Sorbitol is equally effective and less expensive.

Saline Laxatives (Milk of Magnesia, Magnesium Citrate)
PROS: Low cost, easy to use.
CONS: Hypermagnesemia (in patients with renal failure)
DOSE: Up to 60 mL (400 mg/5 mL) a day (constipation).
NOTE: Use with extreme caution in patients with neuromuscular diseases.

STIMULANT LAXATIVES: Bisacodyl (DULCOLAX), Senna (SENOKOT), and Sodium Picosulfate (DULCOLAX DROPS). Exert their effect via alteration of electrolyte transport by the intestinal mucosa. They also increase intestinal motor activity.

PROS: Effective at increasing the number of bowel movements.
CONS: Continuous use can lead to hypokalemia, protein-losing enteropathy, salt overload.

SEVERE CONSTIPATION: Can try Bisacodyl (DULCOLAX) or Glycerin suppositories. Disimpaction should then be attempted if that does not work. If still unsuccessful you can get a water-soluble contrast enema (Gastrografin) to both make sure there is no proximal obstruction and to help things move along.

PHARMACOLOGIC THERAPY: Linaclotide (LINZESS), Plecanatide (TRULANCE), Lubiprostone (AMITIZA), Misoprostol, Colchicine, and Prucalopride (RESOTRAN).

Linaclotide is a minimally absorbed peptide agonist of the guanylate cyclase-C receptor that stimulates intestinal fluid secretion and transit. Plecanatide works in the same fashion.

Lubiprostone is a locally acting chloride channel activator that enhances chloride-rich intestinal fluid secretion. Most common side effect is nausea.

Misoprostol is a prostaglandin analog which has been used to treat some patients with severe constipation. Should not be used in women who could become pregnant.

Colchicine may be effective. Should not be used in patients with renal insufficiency. Can induce a myopathy.

Prucalopride is not available in the US but it is used in Canada. It is a 5HT4 prokinetic agent.