Drug Profile

Lactulose is a synthetic combination of the sugars galactose and fructose. It is not well absorbed from the intestines, and the body responds by secreting water into the intestines. Drugs that reduce constipation this way are called hyperosmotic laxatives. The sugars are also fermented by bacteria in the colon, producing hydrogen gas. (Patients taking the laxatives psyllium or methycellulose  appear to be less likely to pass gas than those taking lactulose.[1]) Both actions expand the colon, which responds by contracting and expelling its contents. Much of the water in the colonic contents is reabsorbed in the colon; the decreased transit time means there is less time for water reabsorption and stools are therefore softer.[2],[3]

In advanced liver disease, ammonia builds up in the body and can enter the brain, causing confusion and even coma, a condition called hepatic encephalopathy. Lactulose slightly acidifies the colon and converts ammonia into ammonium, which is then passed out in the stool.[4] Lactulose is thus an accepted treatment for hepatic encephalopathy.[5]

Hyperosmotic laxatives, such as lactulose, usually take a few days to work. Doses may need adjusting for individual response.[6] Some people dislike the sweet taste.[5],[7] Lactulose is usually taken orally, but it may be administered via enema or nasogastric tube in encephalopathic patients.[5] Laxatives should only be taken for a limited time. If lactulose is used for more than six months or by elderly or debilitated people, electrolytes should be monitored.[8]

When do you really need to take a laxative? You should not take a laxative to “clean out your system” or to make your body act more “normally.” It is untrue that everyone must have a bowel movement daily. Perfectly healthy people may have from three bowel movements per week to three bowel movements per day.

If the frequency of your bowel movements has decreased, if you are having bowel movements less than three times a week, or if you are having difficulty in passing stools, you are constipated, but this does not mean that you need a laxative. It is better to treat simple, occasional constipation without drugs, by eating a high-fiber diet that includes whole-grain breads and cereals, raw vegetables, raw and dried fruits, and beans, and by drinking plenty of nonalcoholic liquids (six to eight glasses per day). This type of diet will both prevent and treat constipation, and it is less costly than taking drugs. Regular exercise—at least 30 minutes per day of swimming, cycling, jogging, or brisk walking—will also help your body maintain regularity.

If you are constipated while traveling or at some other time when it is hard for you to eat properly, it may be appropriate to take a laxative for a short time. The only types of laxatives you should use for self-medication are bulk-forming laxatives such as psyllium or methycellulose or a hyperosmotic laxative such as lactulose. Bulk-forming laxatives usually take effect in 12 hours to three days, compared with docusate (COLACE, SURFAK), which takes effect one or two days after the first dose but may require three to five days of treatment. Even bulk-forming laxatives should only be used occasionally, if possible.

If you are on a special diet such as a low-salt or low-sugar diet, ask your doctor or pharmacist to help you choose a laxative without ingredients you are trying to avoid. Some laxatives contain sugar (up to half of the product), salt (up to 250 milligrams per dose), or the artificial sweetener NutraSweet.

People with diabetes should use lactulose cautiously. Rarely, lactulose causes gas within the bowel wall, a condition called pneumatosis intestinalis that sometimes requires surgery.[9] Infants administered lactulose are especially prone to low blood sodium and dehydration.[4] People who undergo electrocautery procedures during proctoscopy or colonoscopy risk hazard if an electrical spark triggers an explosion with hydrogen gas. Bowel cleansing for these procedures should use a nonfermentable solution.[8]

If diarrhea occurs in the course of treatment for constipation, lactulose should be stopped. Prolonged diarrhea can cause excess sodium in the blood as well as loss of potassium.[5],[10]