Laxative saline

A laxative is most often prescribed for the short-term relief or prevention of constipation. Certain stimulant, emollient, and saline laxatives are used to evacuate the colon for rectal and bowel examinations. Fecal softeners or mineral oil are used prophylactically in patients who should not strain during defecation, such as after anorectal surgery or a myocardial infarction. Psyllium may be used in patients with irritable bowel syndrome and diverticular disease. Fblycarbophil may be prescribed for constipation or diarrhea associated with irritable bowel syndrome and diverticulosis. Mineral oil is... 

Saline laxatives attract or pull water into the intestine, thereby increasing pressure in the intestine, followed by an increase in peristalsis. Magnesium hydroxide (Milk of Magnesia) is a saline laxative. 

Saline laxatives containing magnesium, potassium, or phosphates should be used cautiously in persons with reduced kidney function. Monitor appropriate serum electrolyte concentrations in patients with unstable renal function evidenced by changing serum creatinine or creatinine clearance. 

For most nonhospitalized persons with acute constipation, the infrequent use (less than every few weeks) of most laxative products is acceptable however, before more potent laxative or cathartics are used, relatively simple measures may be tried. For example, acute constipation may be relieved by the use of a tap-water enema or a glycerin suppository if neither is effective, the use of oral sorbitol, low doses of bisacodyl or senna, or saline laxatives (e.g., milk of magnesia) may provide relief. 

Rectal/Bowel examinations Certain stimulant, lubricant, and saline laxatives are used to evacuate the colon for rectal and bowel examinations. 

Saline laxatives like MgS04, Mg(OH)2, Mg2 Citrate and Na+ Phosphates act via their osmotic pressure to retain water in the colon. Other osmotic laxatives are carbohydrates such as lactulose, glycerin, sorbitol, and mannitol. They are not absorbed and are resistant to digestion in the small intestine. Most agents are orally administered. It should be noted however that glycerin, sodium phosphates and sorbitol are formulated for rectal use. From lactulose lactic and acetic acids are formed by intestinal bacteria and apart from its osmotic effects it thus acidifies the content of the colon. The reduction of the pH stimulates motility and secretion. 

If drugs are used, the first choice should be a bulk laxative, e.g. isphagula or sterculia gum. Nonabsorbent carbohydrates with osmotic activity also work well but often cause flatulence. Salinic laxatives like polyethylene glycol and magnesium oxide are very effective but often cause stomach upsets like flatulence and abdominal pain. Tegaserod, a 5-HT4 partial agonist, appears to improve the frequency of bowel movements in those with chronic constipation (see Evans et ah, 2007). 

Laxatives are used to increase stool frequency and reduce stool viscosity. Even with long-term use, bulk laxatives and pure osmolar laxatives do not predispose patients to formation of a cathartic-type colon and should be the initial agents used for chronic constipation after a structural obstructing lesion has been excluded. Laxatives are also used before radiological, endoscopic, and abdominal surgical procedures such preparations quickly empty the colon of fecal material. Nonabsorbable hyperosmolar solutions or saline laxatives are used for this purpose. Classification and comparison of representative laxatives are provided in Table 40.1. 

Bulk-forming agents Saline laxatives (low dose) Saline laxatives (high dose)... 

A new formulation of a saline laxative, Visicol, that is useful to prepare patients for procedures, was approved for use in 2001. Each 2-g tablet contains 1.102 g sodium phosphate monobasic monohydrate and 0.398 g sodium phosphate dibasic anhydrous, for a total of 1.5 g sodium phosphate. Visicol tablets, taken in two doses of 30 g approximately 12 hours apart, induce diarrhea that rapidly and effectively cleanses the entire colon. Each administration has a purgative effect for approximately 1 to 3 hours. 

Laxatives Bulk formers Polycarbophil, psyllium, and methylcellulose preparations. Citrucel, Fibercon, Konsyl, Metamucil, Perdiem, The safest laxatives for chronic use include the bulk formers and stool softeners. Saline laxatives and stimulants may be used acutely but not chronically (see text). Bulk formers hold water and expand in stool, promoting peristalsis. 

Brand name Evac-Q-Mag Class Saline laxatives Manufacturer Generic... 

Saline laxatives (magnesium citrate, magnesium sulfate, sodium sulfate, and disodium phosphate) or saccharide laxatives (sorbitol, mannitol, lactulose) are also used in poisoned patients. Common adverse effects are abdominal cramps, excessive diarrhea, and abdominal distension. Dehydration and electroljde imbalance in children, and hjrpermagnesemia and magnesium toxicity (with magnesium-based cathartics) have also been reported. 

The Austrian Adverse Drug Reactions Advisory Committee received three reports of severe electroljde disturbances associated with an oral bowel-cleansing solution containing sodium phosphate solution (Fleet Phospho-Soda Buffered Saline Laxative Mixture), used as a bowel preparation for colonoscopy (5). Prescribers are advised to be aware of complications of the use of phosphate enemas, particularly in infants, elderly or debilitated patients, patients with congestive heart failure, and patients with impaired renal function. 

Excessive administration of phosphate, particularly intravenously, rectally, or in patients with renal failure, can cause hyperphosphatemia that may lead to hypocalcemia or other severe electrolyte imbalances. Adverse effects occur less frequently following oral consumption, although phosphates act as mild saline laxatives when administered orally or rectally. Consequently, gastrointestinal disturbances including diarrhea, nausea, and vomiting may occur following the use of dibasic sodium phosphate as an excipient in oral formulations. However, the level of dibasic sodium phosphate used as an excipient in a pharmaceutical formulation is not usually associated with adverse effects. 

Monobasic sodium phosphate is used in a wide variety of pharmaceutical formulations as a buffering agent and as a sequestering agent. Therapeutically, monobasic sodium phosphate is used as a mild saline laxative and in the treatment of hypophosphatemia. " ... 

Saline laxatives are more effective when administered with water. The onset of action of organic salts is relatively fast (2 to 6 hours), and that of colloids is relatively slow (1 to 3 days). These agents, which are very effective and safe, should not be used when the intestinal lumen has been narrowed. The prolonged use of saline cathartics may create problems for certain individuals. For example, magnesium salts have been known to cause hypermagnesemia, coma, and death in patients with renal insufficiency. Sodium salts may also be responsible for causing congestive heart failure. 

Human Toxicity Excessive doses may cause mercury poisoning. Antidote Dimercapro] (BAL). Caution If taxation from oral mercurous chloride should not occur, saline laxative must be administered to prevent possibility of mercury poisoning, cf Clinical Toxicology of Commercial Products, R. E. Gosselin et al, Eds. (Williams Wilkins, Baltimore, 4th ed., 1976) Section II, p 95. 

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