LAXA TIVES
A laxative is a synthetic or natural drug (or other substance) used to stimulate the peristaltic action of the large intestines in eliminating fecal waste from the body. The term “laxative” usually refers to mild-acting sub- stances, whereas “cathartic” agents are substances of increasingly drastic action. Laxatives are readily available as over-the-counter drug products and as dietary supplements often used to treat constipation. Constipation refers to the infrequent, difficult, or consistently incomplete passage of small hard feces, usually fewer than three times a week. Constipation may be caused by numerous factors, including lack of adequate fiber or fluid in the diet, prolonged physical inactivity, types of medications (e.g., opioid analgesics, barbiturates, antidepressants, antipsychotics, antihistamines, iron, diuretics, anticonvulsants, angiotensin-converting enzyme inhibitors, calcium channel blockers, and calcium- or aluminum-based antacids), metabolic or endocrine disorders (e.g., diabetes mellitus, hypothyroidism, kidney failure), neurological disorders (e.g., multiple sclerosis, lupus, stroke, Parkinson’s disease, brain tumor), large intestinal disorders (e.g., hernias, tumors, diverticulitis, irritable bowel syndrome), chronically avoiding the urge to empty bowels, or abuse of laxatives. Symptoms include anorexia, dull headache, low back pain, abdominal distension, and lower abdominal distress.
Ancient Egyptian laxative formulations were known to include differ- ent types of salt recipes in liquid, suppository, or ointment form. These included a laxative suppository consisting of honey, vegetable seeds, and ocean salt as well as one of incense, vegetable seeds, fat, oil, and ocean salt. Ancient Arab medicinal laxatives included both senna leaves and pods (fruits). Modern over-the-counter constipation treatments include different types of laxatives. Bulk-forming laxatives allow for the absorption of water from the intestinal lumen, creating a larger stool mass that facilitates evacuation. Once expanded, the stool mass triggers the natural large intestine contraction cycle that leads to expulsion of the feces. They are always administered along with fluids (e.g., water, fruit juice, etc.) and include active fibrous hydrophilic ingredients such as bran, oat, wheat, psyllium seed husks (from Plantagoovata and Plantago major), agar- agar, calcium polycarbophil, flax seed, apple pectin, or various cellulose substances (e.g., methylcellulose).
Hyperosmotic laxatives exert a local irritant effect and an osmotic ef- fect such that water is drawn into the rectum, which results in abdominal distension and stimulates peristaltic bowel movement. They include active ingredients such as glycerin, lactulose, sorbitol solutions, or polyethylene glycol. Saline laxatives are relatively nonabsorbable cations and anions that draw water into the large intestine, thereby causing an in- crease in intracolonic pressure and subsequently an increase in intestinal peristaltic motility. These laxatives include active ingredients such as magnesium hydroxide (milk of magnesia), magnesium citrate and magnesium sulfate (Epsom salts), or sodium phosphate.
Emollient laxatives (stool softeners) allow for water to interact more effectively with stool solids, resulting in a softening of stool consistency. Thus, perirectal strain is avoided during evacuation. They add oily material (e.g., mineral oil), increase water retention in the intestine, or aid the mixing of water and oil components (e.g., with assistance from docusates [surfactants]) in the fecal material. Lubricant laxatives act similarly to emollient laxatives in that lubricants (e.g., mineral oil) soften fecal contents by coating the stool and preventing colonic absorption of fecal fluids, in- cluding water. Lubricants ease the passage of wastes and counteract excessive drying of the intestinal contents.
Stimulant laxatives directly stimulate colonic smooth muscle to pro- mote intestinal peristalsis and the secretion of water into the bowel lu- men. These laxatives include ingredients such as castor oil, casanthranol, bisacodyl, or phenolphthalein (also an acid-base indicator). Herbal stimulant laxatives include senna (both leaves and fruits of Cassia senna), cas- cara (Casara sagrada), buckthorn (also known as frangula), rhubarb root, and dried aloe juice. All of these naturally occurring herbal stimulant lax- atives (along with danthron, another previously marketed stimulant laxative) contain one basic category of chemical compounds, known as anthraquinones. These include both the simple anthrones and the bianthrones (composed of two anthrones linked together). The bianthrones, especially sennosides (as found in rhubarb and senna), are quite active as laxatives. Frequent or regular (chronic) use of stimulant laxatives should be avoided, as serious disruption of natural digestive processes may occur (e.g., malabsorption of nutrients and vitamins, electrolyte and fluid deficiencies, and lack of natural colonic muscle contraction [called “cathartic colon”]).
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