Oral enema
Reading File
Finding Sources
Searching the Web
oral enema bowel preparation types mechanism pharmacology
Finding Sources
Reading File
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Here is a comprehensive overview of oral enema - i.e., oral laxative/bowel preparation agents used to cleanse the bowel.
Oral Enema (Oral Bowel Preparation / Oral Laxatives)
The term "oral enema" refers to solutions or tablets taken by mouth to evacuate the bowel - functionally equivalent to a rectal enema but administered orally. This is distinct from a rectal enema (fluid instilled via the anus). Common clinical uses include:
- Bowel prep before colonoscopy or colorectal surgery
- Relief of severe constipation or fecal impaction
- Disimpaction in children
Classification by Mechanism
1. Osmotic / Saline Laxatives
Draw water into the intestinal lumen osmotically, distending the bowel and stimulating defecation.
| Drug | Trade Name | Route | Onset |
|---|---|---|---|
| Polyethylene glycol (PEG) | GoLYTELY, MiraLAX | Oral | 1-4 hours |
| Magnesium citrate | Citroma | Oral | 1-3 hours |
| Magnesium hydroxide | Milk of Magnesia | Oral | 1-3 hours |
| Lactulose | Constulose, Enulose | Oral | 24-48 hours |
| Sodium phosphate | OsmoPrep, Fleet Oral | Oral/Enema | 1-6 hours |
| Sodium picosulfate + Mg citrate | Prepopik | Oral | 1-3 hours |
PEG (Polyethylene Glycol): The gold standard for colonoscopy prep. It is an inert, nonabsorbable osmotically active polymer mixed with electrolytes (sodium sulfate, NaCl, NaHCO3, KCl) to create an isotonic solution. No significant electrolyte or fluid shifts occur, making it safe for virtually all patients. For full bowel cleansing, 1-2 L is taken the evening before and again 4-6 hours before the procedure. - Katzung's Basic and Clinical Pharmacology, 16th Ed.
Lactulose is a semisynthetic disaccharide that resists GI enzymatic hydrolysis. It reaches the colon intact, where bacteria degrade it into lactic, formic, and acetic acids - raising osmotic pressure, causing fluid accumulation and soft stools. It is also used in hepatic encephalopathy to reduce ammonia absorption. - Lippincott Illustrated Reviews: Pharmacology
Sodium phosphate (OsmoPrep - oral tablets): Used for colonoscopy prep (4 tablets with 8 oz clear fluid every 15 min). Contraindicated in renal failure, CHF, megacolon, bowel obstruction. Risks include hyperphosphatemia, hypocalcemia, hypernatremia, and nephrocalcinosis. - Harriet Lane Handbook, 23rd ed.
2. Stimulant / Irritant Laxatives
Directly stimulate the enteric nervous system and increase colonic fluid secretion.
| Drug | Trade Name | Onset (oral) |
|---|---|---|
| Bisacodyl | Dulcolax, Correctol | 6-12 hours oral; 15-60 min rectal |
| Senna | Ex-Lax, Senokot | 6-12 hours |
| Castor oil | Generic | 2-6 hours |
- Senna: Anthraquinone glycosides (sennosides) act in the colon, stimulating peristalsis and secretion. Useful in opioid-induced constipation (combined with docusate).
- Bisacodyl: Acts directly on nerve fibers in the colonic mucosa. Available as oral tablets (enteric-coated) or suppository. Onset orally: 6-12 hours.
- Castor oil: Hydrolyzed to ricinoleic acid in the small intestine - very irritating, prompts rapid peristalsis. Not commonly recommended due to poor palatability. Contraindicated in pregnancy (can stimulate uterine contractions). - Lippincott Illustrated Reviews: Pharmacology
3. Bulk-Forming Laxatives
Hydrophilic colloids that absorb water and expand in the colon, stimulating peristalsis mechanically.
| Drug | Trade Name |
|---|---|
| Psyllium | Metamucil |
| Methylcellulose | Citrucel |
| Bran | Dietary |
Caution: can cause intestinal obstruction in immobile patients; psyllium can reduce absorption of other oral drugs (separate by 2+ hours). - Lippincott Illustrated Reviews: Pharmacology
4. Stool Softeners (Emollient / Surfactant Laxatives)
Surface-active agents that emulsify with stool, softening it.
- Docusate sodium / calcium (Colace): Slow acting (days); used for prophylaxis, not acute treatment. Do NOT combine with mineral oil (risk of mineral oil absorption).
5. Lubricant Laxatives
- Mineral oil (oral or enema): Coats and lubricates stool for easier passage. Must be taken upright to avoid aspiration and lipoid pneumonia.
- Glycerin suppositories: Local rectal lubricant and stimulant.
6. Prosecretory Agents (newer agents)
- Lubiprostone (Amitiza): Activates chloride channels (ClC-2) in intestinal epithelium - increases luminal fluid secretion. Used for chronic idiopathic constipation and IBS-C. Low risk of electrolyte disturbance or dependency.
- Linaclotide / Plecanatide: Guanylate cyclase-C agonists - increase cAMP-driven secretion and reduce visceral pain.
Bowel Prep Protocol (Home Cleanout - Pediatric)
From Harriet Lane Handbook (23rd ed.):
- Take a stimulant laxative (bisacodyl or senna) with 8 oz liquid
- Drink PEG (polyethylene glycol) solution - full amount in 2 hours
- 1-2 hours later, expect passage of formed/thick brown stool, then progressively liquid/clear stool
- If no stool after 4 hours, drink 1 capful PEG in 8 oz hourly until clear
Key Safety Points
| Agent | Avoid In |
|---|---|
| Sodium phosphate (oral) | Renal failure, CHF, elderly, dehydrated patients |
| Magnesium salts | Renal insufficiency (risk of hypermagnesemia) |
| Castor oil | Pregnancy |
| Mineral oil | Aspiration risk, not in infants <1 year |
| Stimulant laxatives | Infants <1 year, suspected obstruction |
| Phosphate enemas | Infants <1 year |
Chronic laxative misuse (particularly stimulants) can lead to "cathartic colon" - colonic atony, melanosis coli (anthraquinone derivatives), and electrolyte imbalances. - Sleisenger & Fordtran's GI and Liver Disease
This is a shared conversation. Sign in to Orris to start your own chat.