Constipation | Laxatives. Part 2

laxatives and weight loss

Lubricant laxatives

Drug category and usage

Plain mineral oil or emulsified mineral oil emulsions are monograph laxatives for short-term relief (1 week) of constipation.

Mode of action

Lubricant laxatives mix with the contents of the intestinal tract to make elimination of the stool easier.

Warnings and precautions

Lubricant laxatives should not be used in children under 6 years of age, in pregnant women, in bedridden or aged individuals, in individuals who have difficulty in swallowing, or individuals who are experiencing episodes of vomiting or abdominal pain. If an individual has a problem with fecal incontinence, leakage of stool through the anal sphincter may occur with use of mineral oil laxatives. Mineral oil products should not be used with stool softeners.

Recommended dose

Emulsifier mineral may be administered during the day or at bedtime, but plain mineral oil should only be administered at bedtime.

Hyperosmotic and/or saline laxatives

Drug category and usage

Hyperosmotic and saline laxatives may be used occasionally for relief of constipation.

Mode of action

Hyperosmotic and saline laxatives greatly increase the osmotic pressure in the lumen of the intestinal tract and water is drawn into the intestine to equalize pressure. This causes a rapid response in stretch receptors that usually results in watery bowel movements. Glycerin is classified as a hyperosmotic laxative and is restricted to rectal use. Magnesium citrate, magnesium hydroxide, magnesium and mixed phosphate salts (sodium phosphate and sodium biphosphate), all inorganic salts, are classified as saline laxatives and are administered orally. Mixed phosphate salts may also be used rectally.

Warnings and/precautions

Hyperosmotic and saline laxatives should not be used if abdominal pain, nausea, or vomiting is present. If any blood appears in the stool, a physician must be consulted because self-care is not appropriate.

Excessive use of oral hyperosmotic laxatives may result in dehydration in individuals who do not maintain an adequate intake of daily fluids; this can lead to hospitalization and even death. The very young, the elderly, and generally frail individuals are at greatest risk for dehydration. An 8 ounce (230mL) glass of fluid should be taken with every oral dose of a hyperosmotic drug.

Magnesium citrate solution should be stored in a cold place (refrigerator) to prevent degradation of the drug and to increase its palatability. Most hyperosmotic laxatives have a disagreeable taste, which may limit their usefulness. If the daily dose of magnesium exceeds 600 mg and the individual has kidney disease, a physician should be consulted before use. If the individual has kidney disease, oral phosphate laxatives should not be

used without the supervision of a physician. If the daily dose contains more than 115 mg of sodium, a physician should be consulted if the individual is on a low sodium diet. The FDA restricts the packaging of oral phosphate solution to 3 ounces (80 g) to prevent serious adverse effects.

Oral phosphates were recommended frequently by physicians when a thorough bowel cleansing before colonoscopy or bowel surgery was required. The FDA issued a safety alert for both OTC and prescription oral phosphates use for bowel cleansing in December 2008. The FDA received reports of acute phosphate nephropathy and now requires a special warning on all oral phosphate prescription products.25 The FDA alert does not affect the status of rectal phosphate products. Glycerin is restricted to rectal use as a suppository or enema, and it may cause some rectal burning after insertion into the rectum.

Recommended dose

Oral dosing for hyperosmotic drugs appears in table 3.5. Glycerin suppositories should not be used in children under 2 years of age unless supervised by a physician. Suppositories with 1 to 1.7 g glycerin may be used in children aged between 2 and 6 years and are inserted rectally. (These suppositories are referred to as infant suppositories.) Suppositories with 2 to 3 g of glycerin are intended for use in children over 6 years of age and for adults. Glycerin enemas containing 2 to 5mL may be administered to children 2 to 5 years of age, and enemas with 5 to 15mL of glycerin may be used in children age 6 years or over and in adults. A daily dose of mixed phosphate enemas may contain approximately 7 g of dibasic sodium phosphate and 19 g of monobasic sodium biphosphate in 4 ounces (115 mL) of fluid for adults and children aged 12 years and older, and doses of 3.5 g and 9.5 g, respectively, in 2 ounces (58 mL) of fluid for children aged 2 to 11 years of age.22

Stimulant laxatives (secretory or irritant) laxatives

Drug category and usage

Stimulant laxatives are for short-term relief (1 week) of occasional constipation.

Mode of action

Stimulant laxatives promote bowel movements by acting on the mucosal wall of the intestine, hence the name irritant. They may increase secretions into the intestine that stimulate stretch receptors to cause defecation, hence the name secretory or stimulant. Bisacodyl, castor oil, and senna are classified as stimulant laxatives. Castor oil acts on both the small and large intestine, causing a more watery bowel movement, and should not be recommended because it is more likely to cause dehydration than the other stimulant laxatives.

Warnings and precautions

Stimulant laxatives should not be used when abdominal pain, nausea, or vomiting is present. If any blood appears in the stool, a physician must be consulted because self-care is not appropriate. Bisacodyl tablets are enteric coated and should not be crushed or chewed; they should not be taken with milk or within 1 hour of ingesting antacids or milk (dairy) products. Abdominal discomfort or cramps may occur, and burning may occur during defecation. The stimulant laxatives are stored at temperatures lower than 86_F (30_C).

Recommended dose

Oral doses for stimulant laxatives appear in table 3.5. Bisacodyl may be used

as a single 10 mg suppository daily in children 6 to 12 years of age and in

adults; a 5 mg suppository may be used daily in children between 2 and 5 years of age.

Stool softeners

Drug category usage

Stool softeners are intended for short-term relief (1 week) of constipation unless supervised by a physician.

Many physicians recommend long-term use of stool softeners in geriatric patients or patients who requires opiates for pain. Docusate calcium, docusate potassium, and docusate sodium are classified as stool softeners.

Mode of action

Stool softeners act as surface active agents (detergents) that can penetrate dry, hard stools in the large intestine to soften the stool for easier elimination.

Warnings and precautions

Stool softeners should not be used when abdominal pain, nausea, or vomiting is present. If any blood appears in the stool, a physician must be consulted because self-care is not appropriate. Stool softeners should not be used with mineral oil or prescription drugs without consulting a healthcare professional. Special warnings for docusate potassium include: ‘Do not use this drug if it contains more than 975 mg of potassium in the daily dose if you have kidney disease without supervision by a doctor.’ Special warnings for docusate sodium include: ‘Do not use this drug if it contains more than 345 mg of sodium in the daily dose if you are on a low salt diet without supervision by a doctor; do not use this drug if you have kidney disease without supervision of a doctor.’

Carbon dioxide

Drug category and usage

Carbon dioxide suppositories are intended for short-term relief of constipation.

Mode of action

When suppositories containing sodium biphosphate (1.2 to 1.5 g), sodium acid phosphate (0.04 to 0.05 g), and sodium bicarbonate (1 to1.5 g) or sodium bicarbonate (0.6 g) and potassium bitartrate (0.9 g) are used rectally, they produce a chemical reaction that releases carbon dioxide gas. The carbon dioxide gas expands, resulting in stimulation of stretch receptors to initiate a bowel movement.

Recommended dose

Adults and children age 12 years and over may insert one suppository rectally daily. The suppository should be moistened by dipping it in a cup of water for 10 seconds or holding it in under running water for at least 30 seconds before insertion into the rectum.

Bowel preparation kits

Drug category and usage

Bowel preparation kits contain a combination of laxatives that are intended for use when medical procedures, such as colonoscopies and GI surgical procedures, are to be performed. These procedures require the large intestine be free of any fecal material. Physicians may use either prescription or OTC products, which are taken the day before the scheduled procedure for bowel cleansing. Only short-acting laxatives are used for the purpose.22 These products are not to be used unless directed to do so by a physician.

Mode of action

OTC laxatives that have a fast onset of action may be used alone or in combinations. Saline laxatives (mixed phosphates and magnesium citrate) and stimulant laxatives (bisacodyl and sennosides) are used for this purpose.

The mode of action for each appears earlier in this chapter. Oral phosphate products may still be used by physicians for bowel cleansing, but the new required labeling increase their awareness of the serious adverse effects to the kidneys from acute phosphate nephropathy.

Recommended dose

The products are used according to a physician’s directions as a bowel cleansing preparation.

Combination laxatives

The monograph permits two laxatives to be combined in a single product,

providing that each laxative has a different mode of action.

Osmotic laxatives

Drug category and usage

Polyethylene glycol 3350 (PEG 3350) is an osmotic laxative intended for temporary relief of constipation.26

Rx–OTC switched drug Polyethylene glycol 3350.

Mode of action

An osmotic laxative draws water into the intestines to mix with its contents and cause swelling, thus initiating defecation. Unlike hyperosmotic laxatives, which have a very fast action, osmotic laxatives have a slow effect because of their lower osmolarity. While hyperosmotic laxatives are effective within hours, osmotic laxatives take 1 to 3 days to achieve their effect. This slower response also greatly reduces the possibility of dehydration and reduces the risk of causing abdominal gas and cramping.

Warnings and precautions

If an individual has kidney disease, a physician should be contacted before using the drug. Osmotic laxatives should not be used for more than 7 days.

Recommended dose

PEG 3350 is taken once daily as 17 g (one cap full) added to 4 to 8 ounces (115–230 mL) of water or juice. It should not be used by individuals under 17 years of age.