Constipation | Laxatives. Part 1

To understand how to treat constipation we have to know first, how constipation happens and why?

Constipation is a difficulty of defecation (stool passage through the anal orifice), happens due to one of two reasons either Hardness of stool or decreasing pushing power behind the defection and may be both. Hardness of stool may be due to increasing in the hard material content of the stool or decreasing the soft ones which both either due to the alterations of its contents or lack of moisture.

Decreasing the pushing effect behind the defection may be due to certain muscles relaxing effect of some diseases or some medicines or due losing the elasticity of the muscles in old age patients, any how a number of different types of constipation can occur and different types of medications and involvements may take place and that is what we will discuss in the next few lines.

Laxatives (Digging Deeper)

Once digestion and absorption of food are completed, waste products move through the small intestine into the large intestine, where the fecal mass is temporarily stored until defecation occurs. This passage of waste material through the GI tract depends on many factors, but the two most important factors are GI motility and absorption of fluids, primarily water.

Gastric motility is affected by the physical bulk of foods in the diet, the appropriate functioning of the autonomic nervous system, both sympathetic and parasympathetic, hormones, and other substances secreted by the body.

If enough bulk, both solid and liquid, is not present in the lumen of the intestines; receptors in the mucosal lining cannot be activated to move the ingested mass along the GI tract. The sympathetic nervous system controls slow segmental waves for mixing materials that have been ingested, and the parasympathetic nervous system controls peristaltic waves that move the ingested material through the GI tract. The parasympathetic nervous system has a more prominent role in overall GI motility than the sympathetic nervous system.

Hormones and other substances secreted by the body’s tissues and organs may increase or decrease motility along the GI tract and may increase or decrease secretions into the GI tract. The major GI hormones include gastrin, which is secreted by the stomach and stimulates gastric acid and enzyme secretions and increases GI motility; secretin, which is secreted by the small intestine and stimulates the pancreas, gall bladder and liver to increase secretions; and cholecystokinin, which is secreted by the small intestine and slows gastric emptying. The intestine also produces gastric inhibitory peptide, which inhibits gastric acid secretion and gastric motility, and motilin, which stimulates intestinal motility.

The normal balance of these substances allows movement through the GI tract at a rate that permits adequate absorption of nutrients, water, and other fluids. Contents from the stomach have a thin, liquid consistency as they enter the small intestine, where secretions from the liver and gall bladder are added to the duodenum, the first portion of the small intestine. As the mass continues through the duodenum into the jejunum and ilium, the other two portions of the small intestine, most nutrients and fluids are absorbed. The mass becomes less liquid as it reaches the large intestine (colon), where excess water is absorbed, and the semisolid feces remains in the colon until evacuation occurs. The daily volume of fluid entering the GI tract is approximately 7000 mL, which is reduced to approximately 100–200mL of feces ultimately excreted.

A bowel movement (defecation) is achieved by stimulation of stretch receptors in the large intestine and activation of muscles that push the fecal material through the anal sphincter to eliminate the body’s solid waste.

The process of digestion, absorption, and elimination of ingested nutrients is a complicated process involving many factors that must be evaluated before deciding the type of laxative appropriate for solving an individual’s problem of constipation. The categories of drug used to treat constipation include agents that provide bulk and agents that alter GI motility either directly or indirectly. 

Causes

Any abrupt change in eating habits may be a cause of constipation. Traveling though different time zones changes the time that meals are consumed as well as sleeping patterns, and changing the type of food eaten or the volume of fluids ingested also affects bowel habits. Many prescription and OTC drugs reduce GI motility, including opioid analgesics, codeine cough suppressants, antihypertensive medications, antihistamines, antidepressants, diuretics, and antacids. Many common medical conditions may cause constipation, including intestinal obstruction, hypothyroidism, diabetes, Parkinson’s disease, spinal cord injuries, and multiple sclerosis. Constipation is a common complaint among the elderly. Several factors may contribute to constipation including an age-related decrease in GI motility, decline in physical activity and a more sedentary lifestyle, and dietary choices.

Any change in normal bowel habits that causes persistent constipation or diarrhea not associated with any of the previous situations warrants a recommendation to a physician for evaluation. Sudden and persistent changes in bowel habits are frequently the first symptoms of colon cancer in many individuals.

Funny laxatives

Medications

Bulk laxatives

Drug category and usage

Laxatives are drugs that are intended for the short-term relief, 1 week, of the symptoms of constipation. A common misconception is in the definition of constipation. The FDA monograph definition includes the following: (1) infrequent bowel movements; (2) difficulty or pain in during defecation; and (3) excessive dry or insufficient quantity of stools. A common misconception is that a bowel movement is required daily. Medically, the frequency may range from three bowel movements a day to three per week. If an individual experiences a sudden change in bowel habit that lasts for 2 weeks or more, a physician should be consulted because this is often a symptom associated with a more serious condition such as obstruction or colon cancer.

Mode of action

Bulk laxatives are replacements for lack of foods containing fiber, such as fruit and vegetables, in an individual’s diet. The daily diet should contain approximately 25 to 50 g fiber. The lack of bulk results in failure of activation of receptors necessary for defecation. Dietary bran, guar gum, psyllium (plantago seed), cellulose and methylcellulose, malt soup extract, polycarbophil, and polycarbophil calcium are OTC monograph bulk laxatives.

Psyllium also appears in many food products, especially cereals. Fiber binds fats and lipids from foods, and soluble fiber such as oatmeal is more effective than insoluble fiber like psyllium in this process. This reduction of fat and lipid absorption in the GI tract may reduce cholesterol levels, and the FDA allows fiber products in foods to make claims for heart health. Bulk laxatives have a slow onset of action and may take 1 to 3 days for maximum effect. Because they are replacing fiber normally consumed in the diet, they may be used for more than the 7 days period of use recommended for most other laxatives if the cause of constipation is lack of dietary fiber. Some of the causes of lack of dietary fiber are poor food choices by individuals, inability to chew foods that have a high fiber content, inability to digest fiber and/or the creation of intestinal gas, and the cost of some high fiber foods.

Warning and precautions

Taking bulk laxatives without adequate fluid may cause them to swell and block the throat or esophagus, causing choking. These products should not be taken by individuals who have difficulty swallowing. Immediate medical attention should be sought if chest pain, vomiting, or difficulty in swallowing or breathing is experienced after taking these products; if there is no bowel movement; or if abdominal discomfort and pain persist. Inadequate fluid intake while using bulk laxatives may lead to intestinal blockage or obstruction. The bulk laxatives should not be used when abdominal pain, nausea, or vomiting is present. If any blood appears in the stool or vomit, a physician must be consulted because self-care is not appropriate. Cellulose and methylcellulose should not be taken without consulting a physician or pharmacist if an individual is taking salicylate drugs or prescription drugs because of possible drug interactions.

Recommended dosage

All powdered products should be mixed with at least 6 ounces (170 mL) of water or other fluid-like juices. If tablets or wafers containing bulk laxatives are used, they should be followed by an increased intake of fluids.