What Is a Saline Laxative?

Laxatives (catharitics) are drugs that increase intestinal moisture, promote peristalsis, soften stools or lubricate the bowel to promote defecation. Clinically, it is mainly used for functional constipation. Divided into volume, irritant and lubricity, permeability, swelling laxatives and so on.

Laxatives (catharitics) are drugs that increase intestinal moisture, promote peristalsis, soften stools or lubricate the bowel to promote defecation. Clinically, it is mainly used for functional constipation. Divided into volume, irritant and lubricity, permeability, swelling laxatives and so on.
Chinese name
Foreign name
laxatives, catharitics
Increase intestinal moisture and promote peristalsis
Functional constipation

Laxative classification

Bulk laxative

Non-absorbed salt
Magnesium sulfate (MgSO4 · 7H2O) and sodium sulfate (Na2SO4 · 10H2O) are also called salt laxatives. Difficult to absorb in the intestine, a large amount of oral formation of high osmotic pressure to prevent the absorption of water in the intestine, expand the intestine, stimulate the intestinal wall, and promote intestinal peristalsis. In addition, magnesium salts can cause duodenal secretion of cholecystokinin, a hormone that stimulates intestinal fluid secretion and peristalsis. Generally applied on an empty stomach, and drink plenty of water, diarrhea occurs in 2 to 8 hours, and liquid stool is discharged. The cathartic effect is severe, so it is mainly used to exclude patients who need to clean the intestines quickly, such as intestinal toxicants and some worms after taking the worms.
Oral high-concentration magnesium sulfate or direct injection into the duodenum with a catheter caused relaxation of the common bile duct sphincter, contraction of the gallbladder, and a cholestatic effect. Can be used for obstructive jaundice and chronic cystitis.
Magnesium sulfate and sodium sulphate have a sharper diarrhea effect, which can cause reflex pelvic hyperemia and dehydration. Menstrual period, pregnant women and the elderly with caution.
Food cellulose and other substances
1. Lactulose (osmotic laxative) is a disaccharide of galactose and fructose. It is not digested and absorbed in the small intestine, so it can relieve diarrhea. The unabsorbed part enters the colon and is metabolized to lactic acid by bacteria, which further increases the intestinal osmotic pressure and produces a laxative effect.
Lactulose can also lower the pH of the colon contents and reduce the formation of intestinal ammonia; H + can form ammonium ions (NH4 +) with the generated ammonia without being absorbed, thereby reducing blood ammonia. Can be used for chronic portal hypertension and hepatic encephalopathy. It should be noted that the loss of water and electrolytes due to diarrhea can make liver encephalopathy worse.
2. Food cellulose includes natural and semi-synthetic polysaccharides and cellulose derivatives such as methyl cellulose and carboxymethyl cellulose in vegetables and fruits, which are not absorbed by the intestinal tract, increase the intestinal volume and keep the feces soft and soft Good laxative effect. Prevents functional constipation.


Formerly known as "irritating laxatives". A class of drugs that can affect bowel activity and absorb water and electrolytes in the intestinal mucosa and cause catharsis. Including anthraquinones and diphenylmethanes, botanical laxatives such as rhubarb, senna, and aloe vera contain anthraquinone glycosides. It mainly acts on the large intestine and has no effect on the absorption function of the small intestine, so it can be used for acute and chronic constipation. * Phenolic peptide is also a contact laxative. [1]
1. Phenolphthalein (phenolphthalein) forms a soluble sodium salt in the intestine with alkaline intestinal fluid after oral administration, which can promote colonic motility. 6-8 hours after taking the medicine, the soft stool is discharged, and the action is mild.
Suitable for chronic constipation. About 15% of oral phenolphthalein is absorbed. It is excreted from the urine and is red if the urine is alkaline. Part of it is excreted by bile, and there is hepato-intestinal circulation to prolong its action time, so the effect of one dose can be maintained for 3 to 4 days. In case of allergic reactions, enteritis, dermatitis and bleeding tendencies occur. Bisacodyl (bisacodyl) is used to clean the intestines before and after acute and chronic constipation, X-rays, endoscopy, or surgery.
2. Anthroquinones (rhodium, senna, and aloe) and other plants contain anthraquinone glycosides. After oral administration, they are broken down into anthraquinone by bacteria in the large intestine, which can increase the colonic peristalsis. Defecation is performed 6 to 8 hours after medication, and is often used for acute and chronic constipation.

Laxative laxative

Laxative laxatives work by locally smoothing and softening the stool. Suitable for elderly and patients with hemorrhoids and anal surgery.
1. Liquid paraffin is a mineral oil that is not digested and absorbed by the intestinal tract, and has the function of smoothing the intestinal wall and softening feces, which makes the feces easy to be discharged.
2. Glycerin enema is injected into the anus with a 50% concentration of liquid. Due to the high osmotic pressure, the bowel wall is stimulated to cause a bowel reaction, and it has a local lubrication effect, which causes bowel movement within a few minutes. Suitable for children and the elderly.

Hypertonic laxative

Such as magnesium sulfate, magnesium oxide, lactulose, sorbitol, etc., because the contained inorganic (organic) ions are not absorbed and form a hypertonic state in the intestine, water enters the intestinal cavity from the body to help defecation.
Adverse reactions: can cause electrolyte disorders, such as hypermagnesium, hyperpotassium, hypernatremia, and hypocalcemia. Excessive doses of lactulose can cause diarrhea.

Laxatives polyethylene glycols (bulging laxatives)

Polyethylene glycol drugs fix water molecules through the hydrogen bonding of polyethylene glycol 4000. After absorbing water in the intestine, it expands to form colloids, which makes the contents of the intestine softer and larger in volume, and promotes the final completion of defecation. Polyethylene glycol products Polyethylene glycol electrolyte powder is the only product with two indications in domestic polyethylene glycol products. It has a small dose of laxative and a large dose of bowel cleansing. Polyethylene glycol electrolyte powder is purely physical: it does not absorb, does not metabolize, is safe, and has no irritation.

Laxative gastrointestinal motility drug

Such drugs are represented by cisapride, which stimulates intestinal peristalsis by promoting acetylcholine secretion. Erythromycin and its series of drugs can also promote bowel movements.
Adverse reactions: cisapride has adverse effects on the heart, and erythromycin can cause stomach upset. [2]

Laxatives precautions

1. Many patients take various laxatives on their own for a long time and continuously. In fact, once a laxative completely empties the colon, it takes 3-4 days to refill it, so continuous medication is not appropriate.
2. Generally, laxatives take effect 6 to 8 hours after oral administration. Therefore, reasonable time for taking medicine should be before bedtime. In this way, defecation the next morning or after breakfast is more in line with physiological laws.
3. The treatment of constipation, especially habitual constipation, should start with regulating diet and developing regular bowel habits. Eating more vegetables and fruits can often get good results.
4. Different types of laxatives should be selected according to different situations. If the poison is excluded, salt laxatives such as magnesium sulfate and sodium sulfate should be selected. For general constipation, contact laxatives are more commonly used. For the elderly, aneurysms, and anal surgery, lubricating laxatives are better.
5. Patients with abdominal pain should not use laxatives without a clear diagnosis. Aged, fragile, pregnant or menstrual women should not use strong laxatives.
6. The author believes that all the laxatives except cellulose cannot be used for a long time. Can only be used to relieve the urgency. The fundamental solution is to change from life and eating habits.


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