Antidiarrheals are medications used to treat persistent diarrhea. Diarrhea is defined as having loose, watery stools more than three times in a single day. It is a symptom of many conditions and infections and sometimes a side effect of certain medications.

In most cases, diarrhea requires no special treatment and will subside on its own after a day or two. Patients merely need to be sure to drink plenty of fluids to avoid dehydration.

However, sometimes diarrhea is persistent, leading patients to seek out medications. Diarrhea that results from viral infection and other sources, such as surgery or chemotherapy treatment for cancer, may be treated with antidiarrheals. Antidiarrheal medications work in one of two ways – they either thicken the stool or slow spasms that occur in the intestines.

The two chief antidiarrheals – bismuth subsalicylate and loperamide – are available without a prescription (although capsules of loperamide are available by prescription only). Bismuth subsalicylate works by balancing the movement of fluid through the bowels. It also kills germs and binds bacterial toxins, making them less harmful. Loperamide works by slowing both the movement of the intestines and the movement of fluid through the bowels.

In other cases, prescription drugs may be used. Drugs such as diphenoxylate increase intestinal transit time. Antispasmodics can relieve diarrhea by decreasing peristalsis, the series of coordinated, rhythmic muscle contractions that move food through the digestive tract. Other drugs that may be prescribed for persistent diarrhea include opioids and codeine.

In addition, medications and supplements usually considered laxatives may sometimes be used. Psyllium and methylcellulose, typically used as bulking agents for chronic constipation, may relieve some cases of chronic diarrhea.

It is important to note that medications such as loperamide or diphenoxylate may be used only for the symptomatic treatment of patients with acute diarrhea in whom fever is absent or low grade and stools do not contain blood.

Antidiarrheals are not recommended for diarrhea caused by infection with bacteria or a parasite. In such cases, medicine is likely to trap the organism in the intestines and actually prolong the diarrhea. Physicians may prescribe certain antibiotics instead of antidiarrheals for such types of diarrhea.

Types of diarrhea treated with antibiotics include traveler's diarrhea, which occurs from ingesting contaminated food or drink, usually while traveling, and those types caused by certain bacteria (e.g., shigellosis, cholera). Antibiotics are also used to treat significant diarrhea in children and elderly people, and in people with illnesses such as cancer, suppressed immune systems or heart disease.

Antibiotics should not be prescribed for certain conditions, such as diarrhea-associated E. coli 0157:H7 as they may predispose the patient to a condition called hemolytic uremic syndrome (HUS), which is associated with kidney failure.

Antidiarrheals are available in liquid, tablet or capsule forms. Persistent diarrhea that lasts longer than a couple of days after treatment or that is accompanied by fever, or blood or mucus in the stools is often the sign of an underlying illness. Patients who experience such chronic diarrhea should seek medical attention.

In addition, patients who have diarrhea are at high risk of dehydration, which can have severe health consequences. For this reason, it is important to drink plenty of fluids while taking antidiarrheals. Infants and children with diarrhea may avoid dehydration by drinking commercially available oral electrolyte solutions. Patients who experience any of the following symptoms of dehydration should notify their physician:

• Decreased urination
• Dizziness and lightheadedness
• Dryness of mouth
• Increased thirst
• Newly wrinkled skin