Constipation is extremely common, especially in the elderly. That's because they're more likely to have a disease or take
a drug that affects their GI tract, and because bowel muscle strength decreases with age.
The best approach to constipation is to address the cause, by treating the disease or discontinuing an offending drug. Dietary
steps to prevent constipation include increasing fiber and fluid intake. When laxatives are necessary, there are a number
of options to choose from:
Bulk forming products. A common first choice, bulk forming laxatives like psyllium (Metamucil) and methylcellulose (Citrucel) work by increasing
fecal bulk and fluid content. They're generally safe because they're not absorbed systemically, but may take up to 72 hours
to work and cause bloating and increased gas.
Stool softeners. The most common stool softener, docusate (Colace, Diocto, others), works by increasing water and fat content in stool. It's
generally safe but may take 24 – 48 hours to work and have only minor laxative effects. It can cause nausea and may have a
bitter taste. Stimulants/irritants. Drugs such as bisacodyl (Dulcolax, Modane, others) and senna (Ex-Lax, Senokot, others) increase smooth muscle contractions
in the intestines to induce defecation, and may also increase water content in the colon. They act within minutes but may
cause excessive diarrhea, cramping, and dehydration.
Osmotics. Osmotic laxatives, including lactulose (Cholac, Enulose, others) and magnesium hydroxide (Milk of Magnesia), greatly increase
water content in the colon, thereby "flushing" the colon's contents and inducing defecation. They act within hours but may
cause electrolyte disturbances, especially in the elderly and in patients with renal dysfunction.
Source: Bleser, S., Brunton, S., et al. (2005). Management of chronic constipation. J Fam Pract, 54(8), 691.
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