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Laxatives- overview

A review of laxatives commonly used to treat constipation.

Osmotic laxatives-Soluble non absorbable compounds →enter stool →exert osmotic pressure ↑ fluid content of stools→ softening & ↑ ed bulk –> stimulation of peristalsis They increase the amount of water in the large bowel ( can draw fluid into the large bowel or retain the fluid that they are administered with ) Macrogols and lactulose also act as stool softeners First line osmotic laxatives are macrogols – consider using lactulose if macrogols not effective

 

Macrogols -inert polymers of ethylene glycol has electrolytes- so no net gain-loss of water Na or K+ sequester water in the intestinal lumen ↑ ed volume of faecal mass→ taggers peristalsis not absorbed→ excreted unaltered on faeces no change needed in CKD efficacy in treatment of constipation is well established can be used for chronic constipation, disimpaction ( refer to BNF )

Usually safe and well tolerated , GI SEs most common- abdo pain ,diarrhea , vomiting , nausea , dyspepsia , distension , flatulence , anorectal discomfort ( due to expansion of contents of the GI tr & an ↑↑ in motility due to p
 Mild diarrhea – use lower dose Pregnancy-lack of safety data Can be used in breast feeding


 intestinal perforation or obstruction ileus severe inflammatory bowel disorders as Crohn’s disease & ulcerative colitis & toxic megacolon.

 

Lactulose -Semi-synthetic disaccharide – not absorbed from the GI tr Colonic bacteria in colon breaks down lactulose to →low molecular organic acids→leads to ↓↓pH in colonic lumen →Osmotic effect ↑↑ Vol of colonic contents Stimulates peristalsis →Physiological rhythm of colon is reinstated


Encourage adequate fluid intake ( 6-8 cups water ) Flatulence →disappears after couple of days Diarrhoea leading to →electrolyte imbalance , Abd pain Use with care if h/o Lactose intolerance Contraindicated -int obstruction / Perforation

 

Saline purgatives -useful when rapid bowel action required- (bowel prep) free ions draw water into lumen of colon Act within 1-3 hrs Maintain adequate fluid intake Magnesium citrate and Sodium phosphate are common used.

 

Magnesium salts -Have antacid properties Can interact with several medications Use with caution in CKD pts Magnesium hydroxide mixture.

 

Phosphate rectal -Can work in 2-5 mins can lead to electrolyte imbalance Incd phosphate levels – do not use in sig renal impairment saline laxative→fluid accumulation in lower bowel→distension-→peristalsis Fleet Ready to use enema Phosphate enema

 

Sodium citrate rectal -Use in constipation of rectum and sigmoid colon Micolette Micro enema Micralax Micro enema Relaxit Micro enema

 

Stimulant laxatives -Diverse class of agents derived from anthraquinones ( e.g, senna , cascara , castor oil , dantron ) and diphenylmethane ( bisacodyl , sodium picosulfate ) Increase intestinal motility and secretion They can often cause abdominal cramp Act rapidly , well tolerated but caution is advised for indefinite use.

 

Bisacodyl -Dual action →stimulates sensory n endings in L intestine and rectum-→parasympathetic reflexes ↑↑ peristalsis stimulation of defecation , ↓ transit time , stool softening Rectal stimulation → ↑Motility , rectal fullness 5 to 20 mg at night (works in 6-12 hrs when taken orally) Rectal 10 mg →works in 15-60 mins
 Contraindicated ( all stimulant laxatives ) in patients with ileus , intestinal obstruction , acute abdominal conditions as acute appendicitis , cute inflammatory bowel disease , severe dehydration or known hypersensitivity to bisacodyl.

 

Senna -Stimulates motility of L int →accelerated colonic transit Antiabsorptive effect and secretagogue →Enhanced conc of fluids and electrolytes into lumen of colon Shown in controlled trials to soften stools & to ↑↑ the frquency and wet and dry weights of stool Takes 8-12 hrs to act Excreted mainly in faeces Safe to use in pregnancy.

 

Glycerin suppository-Rectal stimulant- mild stimulating action of glycerol Stimulates an osmotic effect in the rectum ( hence cal also be classified as an osmotic laxative ) Works within 15-30 min.

 

Dantron -constipation in terminally ill acts on nerve endings of myenterinc plexus -stimulates muscles of large intestine Known to cause liver and intestinal tumours in rats May cause temporary harmless pink red colouring of urine and perianal skin Acts in 6-12 hrs 1-2 capsule at bed time Normal is 25 mg Dantron , Strong Co Danthramer 37.5 mg Dantron.

 

Sodium picosulfate -contact stimulant laxative , following metabolism in the colon it stimulates the mucosa -> increases the motility of the large intestine and the rectum Large intestine stimulation causes colonic peristalsis with promotion of accumulation of water and electrolytes in the colonic lumen leading to stimulation of defecation , reduction in transit time and softening of stool Rectal stimulation causes ↑ motility & a feeling of rectal fullness – this may also help to restore the call to stool Often combined with magnesium citrate causing a double action 
( stimulant and osmotic ) for e.g CitraFleet ( Bowel prep ) Sold as Dulcolax Adult Pico Liquid in the UK.

 

Bulk forming laxatives -Indigestible , hydrophilic colloids →absorb water ↑↑ fecal mass →distend the colon → stimulates peristalsis maintain adequate fluid intake Bloating & flatulence SEs can take 2-3 days to work can be used 1st line- in the morning.

 

Bulk forming laxatives not recommended in Opioid induced constipation (Opioids prevent the colon responding with propulsive action) May cause painful colic and rarely bowel obstruction

 

Methylcellulose Colloid which absorbs water & swells useful in colostomy , ileostomy & simple diarrhoe diverticular dis and U Colitis

 

Sterculia useful in constipation during pregnancy , ileostomies & colostomies management not absorbed in GI tract works within 12hrs

 

Ispaghula Husk Main constituent is from Plantago ovata Forssk – can absorb water up to 40 times its own weight Ispaghula husk is made of 85 % water soluble fiberts & is partly fermentable and works by hydration of bowel When taken with an adequate amount of liquid it can produce an increased volume of intestinal contents as a result of the high bulking properties which can cause stretch stimulus and trigger defecation Can be useful for patients who would benefit with a high fiber regimen for e.g
○ relief of constipation including constipation in pregnancy & maintenance of regularity
○ patients with haemorrhoids , anal fissures Available agents include – Fybogel ,Isogel ,Ispagel Orange ,Regulan Effect takes 48-72 hrs

 

Stool softeners -Docusate sodium anionic wetting agent ↓↓ surface tension→ water & salt penetrate hard dry faeces prevent Rx ch constipation soften hard , dry stools (in presence of haemorrhoids , anal fissures) orally acts within 1-2 days Rectal-Norgalax Micro-enema works in 5-20 minutes
 Another example of a stool softener is Psyllium

 

Lubricants -Lubricate the intestine and reduce water absorption from intestine Mineral oil , magnesium hydroxide / mineral oil & mineral oil rectal are example of lubricant laxatives

 

Lubiprostone Chloride channel activator-increases intestinal fluid secretion → ↑↑ motility idiopathic constipation or IBS in adults Indicated when -Rx with two different laxatives at highest recommended dose for 6 mts has failed to provide adequate relief and for whom invasive Rx for constipation is being considered It has marketing authorization for ‘ treatment of chronic idiopathic constipation and associated symptoms in adults when response to diet and non-pharmacological measures ( for e.g educational measures , physical activity ) are inappropriate

 

Linaclotide Peptide agonist of guanylate cyclase 2c (an enzyme found in luminal aspect of int epithelium) Elicits pharmacological effect locally in GI tract with minimal systemic absorption GI tract is accelerated and release of intestinal fluid is increased Extracellular cGMP ↑↑ cause a ↓↓ in visceral pain Treatment of moderate to severe irritable bowel syndrome with constipation ( IBS-C ) in adults , literature also mentions use in chronic idiopathic constipation

 

Peripheral opioid receptor antagonist Blocks peripheral effects of opioids while sparing central analgesic effect (because does not cross the blood brain barrier) used in opioid related constipation as an adjunct in palliative care patients Methylnaltrexone subcutaneous inj-acts within 30-60 mins

 

Opioid antagonist with Oxycodone Targinact ( MR Oxycodone with Naloxone ) Severe pain which can only be managed with opioid analgesics Palliative care ( Specialist use ) Intractable constipation despite optimal laxatives Second line for patients with severe idiopathic restless leg syndrome after failure of dopaminergic therapy.

 

Prucalopride selective high affinity 5-HT4 receptor agonist-targets impaired motility-stimulate colonic mass movement Only in women for chronic constipation for whom
○ Rx with atleast two laxatives from different classes at the highest recommended doses for atleast 6 months has failed to provide adequate relief and 
○invasive treatment is being considered To be prescribed by a clinician with experience of treating chronic constipation

REFERENCES

  1. Constipation in adults http://cks.nice.org.uk/constipation#!scenario Medicine.org.uk
  2. British National Formulary
  3. Scottish Palliative Care Guidelines http://www.palliativecareguidelines.scot.nhs.uk/guidelines
/symptom-control/Constipation.aspx
  4. Portalatin, Meredith, and Nathaniel Winstead. “Medical management of constipation.” Clinics in colon and rectal surgery vol. 25,1 (2012): 12-9. doi:10.1055/s-0032-1301754
  5. Drugbank via https://go.drugbank.com/drugs/DB11097
  6. Thomas, Rachel Hutchins, and Kyle Allmond. “Linaclotide (Linzess) for Irritable Bowel syndrome With Constipation and For Chronic Idiopathic Constipation.” P & T : a peer-reviewed journal for formulary management vol. 38,3 (2013): 154-60. ( Abstract )
  7. Lyseng-Williamson, Katherine A. “Macrogol (polyethylene glycol) 4000 without electrolytes in the symptomatic treatment of chronic constipation: a profile of its use.” Drugs & therapy perspectives : for rational drug selection and use vol. 34,7 (2018): 300-310. doi:10.1007/s40267-018-0532-0
  8. Medicine compendium via https://www.medicines.org.uk/emc/product/7709/smpc#INDICATIONS
  9. NICE on Lubiprostone https://www.nice.org.uk/guidance/ta318/documents/constipation-chronic-idiopathic-lubiprostone-final-appraisal-determination-document2

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