Constipation is a condition in which the bowel is evacuated at a longer interval or with difficulty. Drugs for constipation can resolve this issue. Causes of constipation are:

1. Change of environment

2. Emotional tension

3. Disregard of the call to pass motion.

4. Disease or abnormality of gastrointestinal tract

5. Adverse effects of drugs

6. Drying of stools (fecal impaction)

7. Obstruction of intestine and

8. Severe illness with too small food intake

Classification of Drugs for Constipation

Mild Purgatives (Laxatives)

1. Bulk producing drugs for constipation:

  • Isapgol: 4 to 5 gm once or twice a day.
  • Agar-agar: 1 to 6 gm in divided doses.
  • Bran: 12—24 gm daily in divided doses
  • Methyl cellulose: 1 gm, 1—4 times daily
  • Sodium carboxy methyl cellulose: 1.5 gm, 1—4 times daily

2. Stool softeners: Dioctyl sodium sulfosuccinate: 50—500 mg daily

3. Lubricant laxative: Liquid paraffin: 15 ml per day

4. Mild saline purgatives drug for constipation:

Magnesium hydroxide (as 8% W/W suspension—milk of magnesia): 30 ml

Sodium potassium tart rate (Rochelle salt):

8—15 gm

Strong Purgatives (Cathartics)

1. Osmotic purgatives:

Magnesium sulfate (magsulf): 5—15 gm daily

Lactulose: 30—50 ml (3.5 gm per 5 ml) 3 times a day


a. As rectal suppositories: 3 gm

b. As glycerine-edible oil enema: 30—50 ml of each

Polyethylene glycol: 250 ml every 15—20 minutes up to 4 liters over a period of 4 hours.

2. Irritant purgatives;

  • Phenolphthalein: 60—120 mg daily.
  • Sennaglycosides: 0.6 gm (1—2 tabs daily).
  • Bisacodyl: 5—15 mg daily.
  • Cascara sagarada: 1—2 tab at bedtime.
  • Castor oil: 15—25 ml daily.

General Mechanisms of Actions in drugs for constipation

Purgatives generally may act in one of the following ways:

1. By either inhibiting segmenting non- propulsive contractions or stimulating propulsive contractions

2. By retention of intraluminal fluid due to hydrophilic or osmotic mechanisms

3. By decreasing net absorption of fluid due to effects on small and large bowel fluid and electrolyte transport.

Mild Purgatives (Laxatives)

Uses of Laxatives include:

  • To treat constipation.
  • To avoid undue straining at defecation in cases having hernia, haemorrhoid or cardiovascular disease.
  • Before or after surgery of anorectal disease.
  • In bedridden patients.

1. Bulk Producing drugs for constipation

These Drugs for constipation absorb water and increase bulk in the intestine. So they make the stool soft and help in the evacuation. The onset of their action is slow, about 12—24 hours. They are the safest purgatives. In our country, isapgol is most commonly used. Adverse effects are rare. Occasionally, flatulence may occur. This can be relieved by increasing the fluid intake. On chronic use, isapgol decreases plasma cholesterol by interfering with the absorption of bile acids. So to obtain maximum benefit and to avoid the possibility of intestinal obstruction (rarely reported), plenty of fluids should be taken along with these drugs.

Bulk forming laxatives decrease the absortion of other drugs such as salicylates, warfarin, and tetracycline by binding with them. So while prescribing these drugs the dentists should ask the patient to take them 2 hours after the administration of bulk purgatives.

2. Stool Softeners drugs for constipation

Dioctyl sodium sulfosuccinate: It is an effective stool softener. It is a detergent. It is an anionic surfactant. By reducing the surface tension of fluids in the bowl, it softens the stool and permits easier defecation. It also acts as a wetting agent for the bowl because it facilitates the penetration of water into feces by emulsifying the colonic contents. It increases the absorption of mineral oils, so it should not be taken simultaneously with mineral oils.

3. Lubricant Laxative drugs for constipation

Liquid paraffin: It is an inert mineral oil. It lubricates the intestines. It makes the passage of stools smooth and comfortable by forming a film or coating around the stools. It softens the stool by retarding the absorption of water from the stool. It is often recommended in cases in which straining to evacuate may be harmful, e.g. piles, heart attack, pregnant women, after surgery on the rectum or abdomen.

Indiscriminate and prolonged use of liquid paraffin is not desirable because it dissolves the fat-soluble vitamins, e.g. A, D and K and impairs their absorption. So it may cause deficiency of fat soluble vitamins. It prevents complete evacuation of bowels because its presence in rectum inhibits the stimulatory reflexes to the intestine. On aspiration (in dysphagia patients or rarely in normal elderly and weak person on oral ingestion), liquid paraffin has also been reported to cause lipoid pneumonia. Its use is not preferred after surgery for piles because it delays healing. Lastly, leakage of oil per rectum is annoying and embarrassing and may also be a cause of pruritus ani. It should not be taken along with dioctyl sodium sulfosuccinate as the latter promotes its absorption from the intestine.

4. Mild Saline Purgatives drugs for constipation

Magnesium hydroxide: It is a mild laxative so it can be used even by pregnant women and children. On oral ingestion, it builds up an osmotic pressure in the intestinal lumen and draws water into it from the mucosal blood vessels to form the bulk. Thus it makes the stools soft and stimulates peristalsis. Besides purgative action, it counteracts acidity in the stomach. Its action starts after 2 to 6 hours. It may produce flatulence in some people. Plenty of fluid must be taken along with this purgative. Milk of magnesia should be avoided in patients with chronic kidney disease because of difficulty of its excretion.

Sodium potassium tartrate: It is the basic ingredient of commonly used ENO’s fruit salt and Seidlitz powder. The latter consists of two packets; the blue packet contains 2.5 gm of sodium bicarbonate and 7.5 gm of sodium potassium tartrate, the white packet contains 2.2 gm of tartaric acid. The contents of white packet are dissolved in a glass of water and then the contents of blue packet are added to the solution.

The interaction between sodium bicarbonate and tartaric acid yields carbon dioxide and so the drink effervesces. It is pleasant to take and is drunk while it is effervescing. The gas present in the solution distends the stomach and reflexly stimulates movements of the intestines. It also absorbs water from the intestines which assists in forming the bulk and softening of the stools. Its action starts after 3—6 hours. It should not be taken by those who are on a sodium restricted diet, e.g. patients of heart failure, hypertension, etc.

Strong Purgatives drugs for constipation (Cathartics)

Strong purgatives are used as drugs for constipation for causing complete evacuation of the bowel. They should only be used under medical supervision. These purgatives should not be used for treatment of constipation because fully evacuated bowels become inactive (atonic) and after constipation usually follows for which a milder purgative is again needed. However, their indications are:

• As post-purge to flush out worms after the use of an anthelmintic drug.

• To induce labour if the delivery does not occur at the expeded time.

• For complete colonic cleansing prior to gastrointestinal procedures.

• To prepare the bowel before surgery or abdominal X-ray.

• For postoperative or post-myocardial infarction and bedridden patients.

There are two types of strong purgatives drugs for constipation:

• Osmotic purgatives

• Irritant purgatives

Osmotic Purgotives

On oral administration certain salts are not much absorbed from gastrointestinal tract. They are retained there and exert an osmotic effect. So they hold considerable amounts of water and increase the intestinal bulk. In turn, they cause increase in the intestinal motor activity and evacuation by mechanical stimulus.

i. Magnesium sulfate (magsulf): It causes total evacuation of bowel in 1 to 3 hours. So it is usually taken in the morning. It may cause dehydration because of excessive loss of fluids. It may cause serious depression of central nervous system, even if a minute amount of magnesium is absorbed into the bloodstream from the intestines.

ii. Lactulose: This is a synthetic non-absorbable disaccharide. It is metabolized into lactic acid and other organic acids by bacteria in the distal ileum and colon. So lactulose and its metabolites produce evacuation of the bowel by osmotic effect. Further, lactic acid can bind ammonia. Due to this it is used in the treatment of hepatic coma to produce 2—3 soft stools per day.

Lactilol: It is a synthetic disaccharide. It is more palatable than lactulose and has similar actions.

Important features of osmotic purgatives used as drugs for constipation

• Act in the small and large intestines.

• Produce watery evacuation within 3—6 hours.

• Given earl)’ in the morning before breakfast.

• Do not cause irritation.

• To avoid dehydration plenty of water is to be taken.

iii. Glycerine: It softens and lubricates the dried up feces by its osmotic action. It also stimulates rectal contractions. It is employed in the form of suppositories as well as a glycerine-edible oil enema.

iv. Polyethylene glycol:It is a non-absorbable electrolyte sugar that retains water due to its l’iigh osmotic nature. It is used orally in form of a balanced isotonic solution prepared by adding sodium chloride, sodium sulfate, sodium bicarbonate and potassium chloride so that no electrolyte shift occurs across the intestinal wall. So it does not cause dehydration. It is used to clean the bowel before surgery, colonoscopy and radiological procedures.

Irritant Purgatives used as drugs for constipation

Phenolphthalein, senna, glycosides, bisacodyl, cascara sagarada and castor oil are irritant purgatives. They act by causing irritation of the intestines. They usually produce purgation in 3 to 6 hours. Phenolphthalein has a long duration of action as it is absorbed and reexcreted in the intestines (effective for 2 to 3 days).

They may cause gripping or cramping pains in the abdomen. Sometimes there may be erosion of inflamed mucosa leading to passage of mucous in stools. They may cause excessive loss of fluids and electrolytes. Phenolphthalein may induce allergic reactions in 0.01% cases in the form of rashes and pigmentation of the skin. Important precautions in the use of irritant purgatives are that they should not be used:

  • For treatment of chronic constipation
  • In pregnant women
  • In cases with previous history of abdominal pain
  • In feeding mothers because these are secreted in milk
  • If allergic reactions occur by phenolphthalein

Therapeutic uses of purgatives

  • In constipation due to diminished intestinal tone.
  • In drug induced constipation.
  • In food or drug poisoning.
  • In patients with severe neuromuscular disease.
  • In patients with hepatic encephalopathy.
  • To reduce the absorption of ammonia and toxins from colon.
  • In patients with painful anal conditions (fissure, thrombosed piles) and in cardiac disease (acute myocardial infarction), in order to avoid straining during defecation.
  • In patients with an i-leostomy or colostomy to modify the effluent.
  • In children with encopresis and congenital/acquired mega colon,
  • To eliminate the parasites following anthelniintic therapy.
  • To clean the bowel before surgery, colonoscopy and radiological procedures.

[Source: Principles of Pharmacology for Dental Students]