Enema

An enema, also known historically as a clyster, is the administration of liquid into the large intestine through the anus. The term refers both to the procedure and to the fluid or device used to deliver it. Enemas have long been employed in medical practice for bowel cleansing, relieving constipation, administering medication and supporting certain therapeutic procedures. Their use ranges from routine clinical applications to specialised treatments for chronic bowel disorders.

Medical Purposes and General Use

In modern medicine, enemas are primarily used to relieve constipation, treat faecal impaction and prepare the bowel before diagnostic procedures, notably colonoscopy and lower gastrointestinal imaging such as the barium enema. They may also be used to manage traveller’s diarrhoea, provide a route for hydration when intravenous therapy is unsuitable, or administer medicines locally within the large intestine.
The mechanism of action varies according to the type of solution used but generally involves expanding the colon, stimulating peristalsis or softening stool. For effectiveness, the infused liquid is usually retained for five to fifteen minutes, depending on the patient’s tolerance and the solution’s characteristics.

Bowel Cleansing and Acute Treatment

Enemas used as bowel stimulants function similarly to oral laxatives but can be more rapid and effective when oral agents fail or are contraindicated. A low enema clears stool from the rectum, whereas deeper, high or large-volume enemas are intended to reach greater segments of the colon.
Bowel cleansing is enhanced by the mechanical distension caused by liquid volume and, in some preparations, by chemical irritation of the mucosa, which triggers stronger peristaltic contractions. Large-volume enemas are also used at home for occasional constipation, though recurrent or severe cases require medical supervision.

Water-Based and Irritant Solutions

Various solutions are used to achieve specific physiological effects:

• Plain water: Expands the colon mechanically but can cause electrolyte imbalance if retained too long.
• Normal saline: Less irritating than water and maintains electrolyte balance; suitable for longer retention to soften hardened stool.
• Castile soap: Sometimes added to create a soapsuds enema; the mild irritation increases urgency, though liquid soaps and detergents are unsuitable due to excessive mucosal irritation.
• Glycerol: Acts as a mucosal irritant and osmotic laxative, commonly used in dilute form (e.g., 5%) in small-volume enemas or suppositories.

Specialised Solutions

Some traditional and clinical mixtures include:

• Milk and molasses: Heated to just above body temperature, these solutions are not absorbed in the lower bowel, drawing water into the colon and prompting evacuation. They are used effectively in emergency settings with low complication rates.
• Mineral oil: Lubricates and softens stool but may cause irritation or leakage.
• Sodium phosphate (e.g., Fleet enema): Draws water osmotically into the colon. It acts rapidly but can cause cramping and is unsuitable for individuals with certain medical conditions due to electrolyte shifts.

Microenemas

Small-volume enemas, often delivered in pre-packaged units, contain agents designed for rapid action:

• Bisacodyl: A stimulant laxative.
• Dantron (where permitted): A stimulant and softener but restricted due to carcinogenic risk.
• Glycerol: A hyperosmotic agent.
• Sodium lauryl sulphoacetate: A wetting agent used in combination products.
• Sorbitol: An osmotic laxative included in some microenema preparations.

Products containing combinations of these ingredients simplify administration and are suitable where large-volume enemas are contraindicated. Examples include formulations containing sodium citrate, glycerol and sodium lauryl sulphoacetate, or mixtures of docusate sodium and sorbitol, used for faecal impaction and pre-procedural cleansing.

Chronic Treatments and Transanal Irrigation

For individuals with long-term bowel dysfunction, such as obstructed defecation, faecal incontinence or neurogenic bowel disorders, transanal irrigation (TAI) provides a structured approach to bowel management. TAI involves introducing water into the rectum and colon to trigger controlled evacuation. When performed regularly, it can help establish predictable bowel routines and improve continence.
Effectiveness varies markedly among patients, with some reporting substantial improvement while others experience limited benefit. An international consensus published in 2013 provides clinicians with guidance on indications, procedures and best practice for TAI. The term retrograde irrigation distinguishes this method from antegrade procedures such as the Malone antegrade continence enema, where fluid enters the colon through a surgically created channel from the abdominal wall.

Bowel Management and Therapeutic Context

Patients who have a bowel disability—a condition characterised by impaired control over defecation—may rely on structured bowel management programmes. Enemas, including small-volume stimulants or larger cleansing infusions, form part of these regimens, especially when conservative measures prove inadequate. The goal is to support regularity, reduce incontinence episodes, and maintain overall bowel health.