Bulk Producers

These agents are either naturally derived (psyllium), semisynthetic (polycarbophil), or synthetic (methylcellulose). They act by swelling in intestinal fluid, forming a gel that aids in fecal elimination and promoting peristalsis. They may cause flatulence (which is less common with methylcellulose) and abdominal cramping. Bulk-forming laxatives must be taken with sufficient water (8 oz or 240 mL/dose) to avoid becoming lodged in the esophagus and producing obstruction or worsening constipation. Hyper-

sensitivity reactions may occur and rarely may be manifested as an anaphylactic reaction.

Hyperosmotics

These products cause water to enter the lumen of the colon. Lactulose, sorbitol, and glycerin are osmolar sugars. Polyethylene glycol 3350 with electrolytes is most useful for acute complete bowel evacuation prior to GI examination. Polyethylene glycol 3350 without electrolytes is useful in patients who are experiencing acute constipation or who have had inadequate response to other agents.8 Lactulose causes acidification of the contents of the colon, increases water content of the gut, and softens the stool. Glycerin causes local irritation and possesses hyperosmotic action. Osmotic agents may cause flatulence, abdominal cramping, and bloating.

Sorbitol and glycerin may be administered rectally for treatment of constipation. Rectal discomfort and irritation may occur when administered rectally. Glucose levels should be monitored in diabetic patients who ingest oral sorbitol.

Lubricants

Lubricant laxatives work by coating the stool, which allows it to be expelled more easily. The oily film covering the stool also keeps the stool from losing its water to intestinal reabsorption processes. Mineral oil (liquid petrolatum) is a nonprescription heavy oil that should be used with caution, if at all, because it can be aspirated into the lungs and cause lipoid pneumonia when ingested orally. This is of particular concern in the young or the elderly. It may also interfere with the absorption of fat-soluble vitamins.

Table 21-2 Dosage Recommendations for Selected Laxatives and Cathartics

Agent

Adults and Children Ages 12 and Over

Children Ages 6-11 Years

Agents That Cause Softening of Feces in 1-3 Days

Bulk forming agents

Methylcellulose 0.45-3 g po per dose up to

6g/day

Polycarbophil 1 -4 g po daily

Psyllium

Emollients

Docusate sodium

Docusate calcium

Docusate potassium

Lactulose Sorbitol Mineral oil

2.5-30 g po daily

100-300 mg po daily

240 mg po daily

100-300 mg po daily

30-150 mL (as 70% solution) po daily

15-45 mL po daily

On advice of practitioner

On advice of practitioner

50-100 mg po daily

On advice of practitioner

100 mg po daily

2 mL/kg (as 70% solution) po daily

5-15 mL po daily

Agents That Result in Soft or Semifluid Stool in 6-12 Hours

Bisacodyl (oral)

5-15 mg po daily 30 mg po daily for complete bowel evacuation

mg/kg) po daily

Senna

12-50 mg po once or twice daily

6-25 mg po once or twice daily

Agents That Cause Watery Evacuation in 1-6 Hours

Magnesium citrate1'

Magnesium hydroxide'

Magnesium sulfate'

Bisacodyl (suppository)

Polyethylene glycol 3350

120-300 mLpo daily

30-60 mL po daily ( 15-30 mL of concentrate po daily)

10-30 g po daily 10 mg recta I ly

100-150 mLpo daily

5-10 g po daily

5 mg rectal ly (1/2 suppository)

17 g in 8 oz (240 mL) water Safety and po once daily; do not use efficacy not longer than 2 weeks established po, orally.

"Magnesium can accumulate in renal dysfunction.

Adapted from Spruill WJ, Wade WE. Diarrhea, constipation and irritable bowel syndrome. In: DiPiro JT, Talbert RL, Yee GC, et al. (eds.), Pharmacotherapy: A Pathophysiologic Approach. 7th ed. New York; McGraw-Hill; 2008:617-632, with permission.

Stimulant Laxatives

Diphenylmethane derivatives (e.g., bisacodyl) and anthraquinones (e.g., senna) have a selective action on the nerve plexus of intestinal smooth muscle leading to enhanced motility. Enteric-coated bisacodyl tablets should be swallowed whole to avoid gastric irritation and vomiting. Ingestion should be avoided within 1 to 2 hours of antacids, H2-receptor antagonists, proton pump inhibitors, and milk. The onset of effect is rapid but the effects can be harsh (cramping), depending on the dose taken. Castor oil is another member of this class that is used less frequently. Castor oil is classified as Pregnancy Category X. It is associated with uterine contractions and rupture. The use of castor oil in breast-feeding is considered as "possibly unsafe."

Emollients

Also known as surfactants and stool softeners, emollients (e.g., salts of docusate) act by increasing the surface-wetting action on the stool leading to a softening effect. They reduce friction and make the stool easier to pass. These agents are not recommended for treating constipation of long duration.

Saline Agents

Salts of sodium, magnesium, and phosphate pull water into the lumen of the intestines resulting in increased enteral pressure. Magnesium and phosphate may accumulate in patients with renal dysfunction. Principal concerns with sodium phosphate derivative use include dehydration, hypernatremia, hyperphosphotemia, acidosis, hypocalcemia, and worsening renal function. Patients with congestive heart failure and renal dysfunction should be advised to avoid these agents. In 2009, nonprescription oral sodium phosphate solutions were voluntarily recalled by the manufacturer because of the risk of acute phosphate nephropathy. Prescription products contain a black-box warning about use in high-risk patients.

Tegaserod Maleate

Tegaserod maleate (Zelnorm) is a partial serotonin (5-HT4) receptor agonist that causes an increase in peristaltic activity and intestinal secretion, and moderation of visceral sensitivity. It increases the frequency of bowel movements and reduces abdominal discomfort, bloating, and straining. The availability of tegaserod maleate is limited to emergency situations in women who are under the age of 55 years and who have a diagnosis of chronic idiopathic constipation who meet specific guidelines. Tegaserod availability was limited because postmarketing safety evaluation found that patients receiving it were at higher risk of suffering cardiac events such as stroke, heart attack, and unstable angina when compared with patients receiving placebo.

Lubiprostone

Lubiprostone (Amitiza), abicyclic acid oral agent, is approved for treatment of chronic idiopathic constipation in adults. It has not been studied in children. Lubiprostone acts locally on intestinal chloride channels and increases intestinal fluid secretion, resulting in increased intestinal motility and thereby increasing the passage of stool.9

Lubiprostone is contraindicated in patients with a history of mechanical GI obstruction and should not be used in patients suspected of having GI obstruction. Safety has not been established in pregnant women; animal studies indicated the potential to cause fetal loss. Women who could become pregnant should have a negative pregnancy test result prior to beginning therapy with lubiprostone.

GI adverse events reported with lubiprostone include nausea, diarrhea, abdominal distention, abdominal pain, flatulence, vomiting, loose stools, and dyspepsia. Nausea is a prominent adverse effect and may be minimized when lubiprostone is taken with food.

The recommended dose of lubiprostone is 24 mcg orally twice daily with food and water. Studies evaluated lubiprostone use for no longer than 4 weeks. Patients should be assessed periodically for the need to continue therapy.

Methylnaltrexone Bromide

Methylnaltrexone bromide (Relistor) is indicated for opioid-induced constipation in patients with advanced illness, receiving palliative care, and who have experienced insufficient response to laxative therapy. It is a selective antagonist of opioid binding at the ^-receptor. It has limited ability to cross to the blood-brain barrier and causes laxation in patients with opioid-induced constipation without reducing the analgesic effects of opioids or inducing opioid withdrawal. Methynaltrexone bromide is administered subcutaneously no more than once daily or every other day at individualized dosages based on patient weight. In patients with renal impairment (creatinine clearance less than 30 mL/min) the dose should be reduced by 50%. The most common side effects are abdominal pain, flatulence, nausea, dizziness, and diarrhea. It is contraindicated in known or suspected GI obstruction.

Treatment Recommendations

Slow-transit constipation can be treated with chronic administration of hyperosmotic laxatives. Senna, bisacodyl, and other stimulants should be used only when the others fail to deliver the desired effect.

Laxatives may provide appropriate relief when constipation occurs during the postpartum period, when not breastfeeding, and in immobile patients. Patients who are not constipated but who need to avoid straining (e.g., patients with hemorrhoids, hernia, or myocardial infarction) may benefit from stool softeners or mild laxatives such as polyethylene glycol 3350.

Laxatives should not be given to children younger than 6 years of age unless prescribed by a physician. Because children may not be able to describe their symptoms well, they should be evaluated by a physician before being given a laxative. Treating secondary causes may resolve the constipation without the use of laxatives. As in adults, children benefit from a healthy balanced diet, adequate fluid, and regular exercise.

Because many elderly persons experience constipation, laxative use is sometimes viewed as a normal part of daily life. However, oral ingestion of mineral oil can be a special hazard in bedridden elderly persons because it can lead to pneumonia through inhalation of oil droplets into the lungs. Lactulose maybe a better choice in this situation. Regular use of any laxative that affects fluid and electrolytes may result in significant unwanted adverse effects.

Patient Encounter 1

DB is a 72-year-old woman who complains of small, hard stools for the last 3 weeks. She noted that lately she has to strain to have bowel movements. She states that this difficulty with having bowel movements has occurred off and on for several months. She denies abdominal pain. She has a history of hypertension, osteoarthritis, and Type

2 diabetes mellitus.

What general approach to this patient should be employed? What are the possible contributing causes of her constipation?

What nonpharmacologic and pharmacologic therapies would be appropriate for her condition?

Bulk producers are commonly used during pregnancy. Stool softeners (Pregnancy Category C) are probably safe to use at any time during a pregnancy because they are poorly absorbed. Lactulose and magnesium products are classified as Pregnancy Category B. Specifically, no human studies are available concerning use of lactulose in pregnant women. Magnesium-based antacids are not classified according to pregnancy categories and are associated with low-risk and minimal absorption in pregnant women. Long-term use of magnesium citrate should be avoided (Pregnancy Category B).

To avoid constipation, pregnant women should be advised to eat regular meals that are balanced among fruits, vegetables, and whole grains; maintain adequate water intake; and get appropriate exercise.

Patients with the following conditions should use laxatives only under the supervision of a health care provider: (a) colostomy, (b) diabetes mellitus (some laxatives contain large amounts of sugars such as dextrose, galactose, and/or sucrose), (c) heart disease (some products contain sodium), (d) kidney disease, and (e) swallowing difficulty (bulk-formers may produce esophageal obstruction).

Diabetes Sustenance

Diabetes Sustenance

Get All The Support And Guidance You Need To Be A Success At Dealing With Diabetes The Healthy Way. This Book Is One Of The Most Valuable Resources In The World When It Comes To Learning How Nutritional Supplements Can Control Sugar Levels.

Get My Free Ebook


Post a comment