Constipation happens when hard, dry stool moves slowly through the large intestine, making it difficult to have a bowel movement.
Many cases of constipation are due to a lack of fibre in a person’s diet. A high-fibre diet is the best solution for prophylaxis and treatment of constipation.
There is in general an overuse of laxatives because people often consider it abnormal not to have a daily bowel movement. They consequently then take laxatives more often than what is necessary.
Although it is generally safe to use laxatives, excessive use may lead to side effects, e.g. hyperkalaemia and other complications, such as damage to the colon. This may impair the normal functioning of the colon and consequently the need for more laxatives to manage the condition. Furthermore, repeated use of stimulant laxatives could lead to loss of water and electrolytes.
There are various types of laxatives available on the market. Combination preparations of these options have not shown more benefits than the use of single component medicines.
Types of laxatives
Bulk-forming laxatives
These laxatives act by softening and increasing the faecal mass and this improves peristalsis due to the increased bulk.
Examples:
- Ispaghula (also known as psyllium) – It is made from the dried ripe seeds of the Plantago Additionally, it may reduce cholesterol and be useful in IBS (irritable bowel syndrome).
- Sterculia –It is the gum from the Sterculia plant which absorbs moisture and increases the faecal volume. It is indicated for use in constipation, IBS and diverticular disease.
- Methylcellulose – It increases faecal volume by absorbing moisture, resulting in bulk mass which encourages peristalsis.
Irritant laxatives
To avoid chronic colonic changes, physiological and psychological dependence, use these laxatives only for short-term indications.
Examples:
- Bisacodyl – Available as oral medication as well as suppositories. It acts in the lumen of the colon and not systemically, because less than 5 % of bisacodyl is absorbed systemically.
- Oral medicationTherapeutic effect achieved within 6 to 8 hours.
- Suppositories With rectal administration the bowel is usually evacuated in 15 to 60 minutes.
- Senna – It acts by stimulating the accumulation of water and electrolytes in the lumen of the bowel and thereby enhancing peristalsis. Senna usually produces an effect in 6 to 8 hours.
- Sodium picosulphate – Bacteria in the colon metabolise it to the active metabolite of bisacodyl.
Osmotically acting laxatives
These laxatives are used for acute and rapid evacuation of the bowel, and they significantly improve bowel cleansing. They draw fluid into the bowel by osmosis. It may be given orally or rectally.
Prolonged use is not recommended, except for lactulose.
For patients undergoing a colonoscopy, it is recommended to take half the dose the evening before the procedure and the other half the next morning, 4 to 6 hours before the procedure.
Examples:
Lactulose – Used for acute and chronic constipation.
Magnesium salts – Used when rapid bowel evacuation is required. Use occasionally.
Sodium salts – Not recommended in patients where sodium or water retention may be a problem. Encourage adequate fluid intake.
Sorbitol – It acts due to the osmotic effect. The glycaemic control in diabetes patients may be altered with regular use. It can be given orally, or as an enema.
Rectal preparations
Rectal preparations should not be given orally.
Enemas are sometimes given to soften an impacted stool. Enemas and suppositories should be used short term only. Rectal preparations include bisacodyl, sodium phosphate, glycerine and sorbitol.
Reference
- South African Medicines Formulary. 13th 2020. Pages 58-62.
