The main principle behind the treatment of constipation is to treat the underlying problem. For instance, correcting hypothyroidism or hypercalcaemia is preferable to using laxatives to stimulate the bowel. However, as most cases of serious constipation have multifactorial causes, treatment usually requires one or more laxatives which should be chosen based on the individual patient's needs.
A number of classes of laxatives and stool softeners exist ( Table 3 ). Understanding their mechanisms of action makes it easier to determine their roles in treating the constipated patient. In cases of severe constipation, it is generally best to start by softening and removing the hard stool below, then to treat from above.
Fibre absorbs water, increases stool bulk, and in doing so stimulates the bowel to decrease stool transit time. It is readily available in fruits and raw vegetables, whole grain breads and cereals or as an additive at health food stores. For those people who cannot add enough natural fibre to their diets, several formulations of bulk-forming psyllium products are available, in cookie, pill, or granule form, or as a powder added to juice or water. However, all these preparations are associated, at least initially, with increased flatus. A semi-synthetic fibre, methylcellulose, tends to decrease this side effect.
Stool softeners, such as docusate sodium (or calcium) and mineral oil, are emollient laxatives which act by decreasing surface tension to allow water to enter the bowel more readily making stool softer, which makes it easier and less painful to pass. Softeners are ineffective for chronic constipation but have a place for patients with anal fissures or hemorrhoids. Mineral oil is not recommended because of its potential to deplete fat soluble vitamins and increase the risk of lipoid aspiration pneumonia in patients who have swallowing difficulties. Overnight mineral oil retention enemas are often useful for softening and lubricating hard or impacted stool prior to starting aggressive oral measures.
Stimulant laxatives increase bowel motility by stimulating the colon. This class of laxatives includes anthraquinones (senna, cascara) and bisacodyl, which may be administered either orally or rectally. It is essential that all patients assigned to a regular dose of opioids be offered a stimulant laxative.
Osmotic laxatives draw water into the bowel because they are hypertonic, essentially flushing the colon. Examples of osmotic laxatives include milk of magnesia (which also softens stools), sodium phosphates and magnesium citrate.8 Although very effective, they should be used with caution in older adults and in patients with renal impairment because of the risk of dehydration and electrolyte disturbances.
Nondigestible sugars (lactulose and sorbitol) are also osmotic laxatives. However, the former (lactulose) may be broken down by colonic flora and produce an uncomfortable amount of gas. For this reason, it is not considered a first-line treatment.
Sodium phosphates and soap suds in tap water, administered rectally, are quite effective in clearing the distal bowel. They should be considered in serious cases before using aggressive oral measures.
Polyethylene glycol acts in a similar way to the previous class of laxatives. As an iso-osmotic laxative, however, it causes no fluid or electrolyte shifts, which makes it safer for use among older adults. Its main disadvantage is the volume of fluid (4 L) that needs to be ingested; many people, particularly older adults, are unable to tolerate this.
There are many alternative, nonmedical therapies for constipation. They include but are not limited to herbal supplements, homeopathy, massage therapy, reflexology and yoga. Although potentially helpful, it is important to identify any such treatments and ensure that they do not interact with any medical therapy being offered.
Constipation is a common condition, especially among older adults and the cause is often multifactorial. Treatment of older adults is often complicated by comorbidities including polypharmacy and cognitive impairment. Like many illnesses, constipation is often easier to prevent than it is to treat. If left undiagnosed and untreated, constipation may lead to very serious complications and death.
It is essential to use a rational, detailed approach to the evaluation of the patient with constipation. If possible, the underlying causes should be corrected, and laxatives should be tailored to the patients' needs.
Geriatrics and Aging. 2007;10(10):654-660. © 2007 1453987 Ontario, Ltd.