Laxatives

Laxatives are a category of medications frequently used to address constipation and various other gastrointestinal medical conditions. Laxatives can provide relief for patients with irritable bowel syndrome with constipation, chronic idiopathic constipation, and opioid-induced constipation. Besides addressing constipation, laxatives are occasionally used to empty the bowels before procedures such as colonoscopies. 

There are 4 main types of laxatives:

Bulk-forming laxatives

• Bulk-forming laxatives work by increasing the "bulk" or weight of poo, which in turn stimulates your bowel.

• They take 2 or 3 days to work.

They include:

Fybogel (ispaghula husk)

methylcellulose

Osmotic laxatives 

• Osmotic laxatives draw water from the rest of the body into your bowel to soften poo and make it easier to pass.

• They take 2 or 3 days to work.

They include:

lactulose (also called by the brand names Duphalac and Lactugal)

macrogol (also called by the brand names Movicol, Laxido, CosmoCol, Molaxole and Molative)

polyethylene glycol

Stimulant laxatives

• These stimulate the muscles that line your gut, helping them to move poo along to your back passage.

• They take 6 to 12 hours to work.

They include:

bisacodyl (also called by the brand name Dulcolax)

senna (also called by the brand name Senokot)

sodium picosulfate

stool softener laxatives

• This type of laxative works by letting water into poo to soften it and make it easier to pass.

They include:

arachis oil

docusate

Their primary mechanism involves enhancing digestion and promoting bowel movements, thereby facilitating the process of bodily excretion. Laxatives can provide relief for patients with irritable bowel syndrome with constipation, chronic idiopathic constipation, and opioid-induced constipation.

The pharmacokinetics of laxatives can vary depending on their type and formulation.

1- Absorption: 

Bulk-forming laxatives: They are not absorbed systemically and act primarily within the gastrointestinal tract.

Osmotic laxatives: They are poorly absorbed in the intestine and remain within the gastrointestinal tract, where they exert their effects by drawing water into the bowel.

Stimulant laxatives: Absorption can vary depending on the specific agent, but generally, they are minimally absorbed and exert their effects primarily within the gastrointestinal tract.

Stool softeners: They are minimally absorbed and primarily act locally within the gastrointestinal tract.

2- Distribution: 

Since most laxatives are not extensively absorbed into the bloodstream, distribution beyond the gastrointestinal tract is limited.

3- Metabolism:

Many laxatives undergo minimal metabolism, particularly those that are not absorbed systemically. They are often excreted unchanged or as metabolites in feces.

Some laxatives, particularly those that are absorbed systemically, may undergo hepatic metabolism before being excreted.

4. Excretion:

Bulk-forming laxatives: Excreted primarily in feces.

Osmotic laxatives: Excreted primarily in urine and feces.

Stimulant laxatives: Excreted primarily in feces.

Stool softeners: Excreted primarily in feces.

• Laxatives are a category of medications frequently used to address constipation and various other gastrointestinal medical conditions. 

• Laxatives can provide relief for patients with irritable bowel syndrome (IBS) with constipation, chronic idiopathic constipation (CIC), and opioid-induced constipation. 

• Constipation is a common diagnosis that requires proper evaluation and appropriate treatment. Notably, laxative therapy is not the sole treatment for constipation. Initial management should involve lifestyle changes, including consuming increased fluids and fiber-rich foods, such as asparagus, broccoli, Brussels sprouts, cabbage, and spinach, into their diet. 

Like most medicines, laxatives can cause side effects. They're usually mild and should pass once you stop taking the laxative.

The side effects you may get will depend on the type of laxative you're taking, but common side effects of most laxatives include:

• bloating.

• farting.

• tummy cramps.

• feeling sick.

• dehydration, which can make you feel lightheaded, have headaches and have pee that's a darker color than normal.

Using laxatives too often or for too long can also cause diarrhea, the bowel becoming blocked by large, dry poo (intestinal obstruction), and unbalanced salts and minerals in your body.

• Intestinal obstruction or perforation.

• Paralytic ileus.

• Colonic atony or faecal impaction (bulk-forming laxatives).

• Crohn's disease or ulcerative colitis.

• Toxic megacolon.

• Severe dehydration (bisacodyl).

• Galactosaemia (lactulose).

• History of hypersensitivity to peanuts (arachis oil enema).

Dose

Bulk-forming laxatives:

Psyllium: One tablespoon orally 1 to 3 times daily.

Methylcellulose: One tablespoon powder or 2000 mg fiber caplets thrice daily.

Osmotic agents:

Lactulose: For constipation, 10 to 20 g (15 to 30 mL) orally daily; the dose may be increased to 40 g (60 mL) daily. For hepatic encephalopathy, 20 to 30 g (30 to 45 mL) orally every hour to induce rapid bowel movement.

Sorbitol: 30 to 150 mL orally daily. It can also be administered as a 120 mL (30%) solution rectal enema. 

Glycerin (glycerol): One suppository (2 or 3 g) per rectum for 15 minutes daily.

Stimulant laxatives:

Bisacodyl: 5 to 15 mg as enteric oral tablets daily. Bisacodyl can also be administered as a 10 mg suppository per rectum one time per day for 15 to 60 minutes. Several studies and review articles have raised concerns about the effectiveness of docusate in preventing constipation; clinical judgment should be based on response to therapy.[14]

Senna: Available as an 8.6 mg tablet. Administer 1 to 2 tablets orally, 1 or 2 times per day.

Lubricants: 

Mineral oil: Given in single or divided doses orally to 45 mL in 24 hours. It can also be administered rectally as a single dose (118 mL).

administration

Laxatives are usually taken orally or as suppositories. Oral formulations include tablets, capsules, powders, chewable tablets, and liquids. Data presented in this section are from product labeling information.

• Laxatives can potentially interfere with the adsorption/function of other drugs by several different mechanisms, such as:

  • -decrease of the intestinal or colonic transit time

  • -modifications of the gastric pH

  • -inhibition of cytochrome P450 enzyme activity

• As stated above, however, it is quite disappointing that relatively little attention has been paid by researchers to the issue of drug interactions with laxatives. In fact, not withstanding the lack of high quality studies investigating these aspects, there is scattered evidence that laxatives, including the OTC ones, may be involved in drug–drug interactions (DDI) 

• Some of these evidences will be briefly discussed here. For instance, a study conducted in healthy volunteers demonstrated that the concomitant administration of macrogol 4000 and of a single dose of digoxin reduced the intestinal adsorption of digoxin, even though there were no consequences on heart rate and atrioventricular conduction 

• Another study, conducted in patients with heart failure, showed that the combined use of sennosides and digoxin was associated with a modest increased risk of digoxin toxicity, requiring hospital admission, in these patients

• One of the most widely used OTC laxative, also thanks to its relatively low costs and good efficacy, is represented by magnesium oxide; however, it must be kept in mind that there is some evidence that the administration of this drug increases the gastric pH, leading to decreased concentrations of antipsychotic drugs, when co-administered 

• Although there is some concern on the simultaneous use of laxatives and coumarin anticoagulants, the scientific evidence supporting this claim is scarce; however, a moderate but significant risk of increased anticoagulation has been demonstrated only for the concomitant administration of lactulose 

• Bulk-forming laxatives: fiber, psyllium, or polycarbophil.

• Emollient stool softeners: docusate.

• Osmotic laxatives: lactulose, macrogol.

• Stimulant laxatives: sennosides (Senexon, Senokot, Black Draught), bisacodyl (Feen-A Mint, Correctol, Dulcolax, Carters Little Pills).