Constipation Flashcards

Question

What are bulk forming laxative and provide some examples?

Answer 1

Works by increasing the mass of your stools which in turn stimulates your bowel. 1. Ispaghula husk e.g. Fybogel 3.5g/sachet - 1 sachet BD (12yrs and over) - Sachets which your pour into a full glass of water and take straight away - Preferably after meals (NOT just before bed) - Take 30min - 1hr before or after other medications -Remains effective despite long term use 2. Methylcellulose e.g. Celevac - 500mg tablets - 3-6 tablets BD with at least 300ml of liquid - Break tablets in the mouth before swallowing Do NOT take just before bed (as these laxatives increase the volume of stool, and you have less/absent peristalsis at night time, taking these will cause the opposite effect) Ensure good fluid intake is maintained (to draw water into the stools) Takes 2-3 days for effect

Answer 2

1. Macrogol E.g. Movicol, Cosmocol, Laxido - 1-3 sachets daily, in divided doses - Sachets to dissolve in 125ml of water - Can be high in sodium - Contraindicated in Hypertension, heart disease, Renal - Do not take other oral medicines 1 hour before or after dose - Takes 1-3 days for effect 2. Lactulose - 15-45ml daily - Can cause bloating and colic - Caution if intolerant to lactulose - NO ISSUE for diabetic patients - Up to 2 days for effect 3. Magnesium hydroxide E.g. Milk of Magnesia liquid - Mainly seen as liquid: 30-45ml PRN - Dose to be given at bedtime - Can be abused as it purgative (strong effect) - Commonly seen OTC (max 3 days) - Around 3-6 hours to take effect 4. Docusate - Up to 500mg daily in divided doses - 12-72 hours for effect of tablets - 15mins for effect from suppositories - Softening agent and a stimulant

Answer 3

- These are often used for their quick action and strong laxative effect * Arachis oil enema contains PEANUT oil - beware for patients who are allergic *

Answer 4

Stimulant laxatives are usually for short term use as they are said to cause a lazy bowel. They work directly on the smooth muscle on the bowel, essentially promoting peristalsis. 1. Senna E.g. Senokot: - Tablets and syrup - 7.5-15mg daily - Onset of action 8-12 hours - Syrup os unpleasant 2. Dantron E.g. Co-danthramer or Co-danthrusate: - Co-danthramer includes PEG - Co-danthrusate includes docusate - Colours urine red - Avoid prolonged contact with skin - ONLY in terminally ill patients (potential carcinogen- causes cancer) - Oral solution - Onset of action 6-12 hours 3. Sodium pico sulphate i.e. Dulcolax - 5-10mg once daily - Tablets and syrup - Onset of action 10-14hours 4. Bisacodyl i.e. Duclolax - Acts on the small intestine - 5-10mg once daily; Increased if necessary up to 20mg once daily - Tablets act in 10-12 hours - Suppositories act in 20-60 minutes - Suppositories can cause local inflammation

Answer 5

- A selective serotonin 5HT4-receptor agonist with pro kinetic properties - Should only be prescribed by clinicians experienced in treating chronic constipation after careful review - 2mg tablets once daily, review treatment if no response after 4 weeks. (Reduced dose in elderly) - Side effects: Headache and GI disturbances - Increased doses will NOT improve response - 1-2 weeks for effect Mechanism of action: - 5HT4 receptors are present in GI tract, especially myenteric plexus - 5HT4 activation leads to increased release of ACh - Hence we get an increase in rest and digest/parasympathetic drive - This increases peristalsis and propulsion

Answer 6

The mechanism of action depends on type. - Typically, polysaccharides increase osmolality in gut when broken down, causing water retention - Retention of water in the GIT, so expanding and softening the stool - Bulkier stools distend the colon - Promotion of peristalsis via stimulating colonic mucosal receptors/stretch receptors - This leads to acetylcholine release (increased parasympathetic drive) - ACh activates muscarinic acetylcholine receptors (mostly M2 and M3 subtypes) - Increased peristalsis - Also creates mucus layer in intestinal lining which facilitates defecation

Answer 7

- Poorly absorbed so act as osmotic agents and increase water retention in the gut lumen - As hyperosmolar agents, they are absorbed into stool by osmosis, making it softer - Softer stools are easier to pass - Many osmotic laxatives also contain Mg2+ (Magnesium) - Mg2+ triggers release of cholecystokinin (CCK) - CCK increases intestinal secretions and colonic motility - Decreases transit time through gut

Answer 8

- Stimulate local reflexes of myenteric nerve plexus of the gut - Irritate nerve endings in wall of intestine - Motor effect on gut wall-increases propulsion - Increase secretion of water into the bowel - Increases gut motility and decreased transit time

Answer 9

- Sometimes known as emollient laxatives - Some work as surface wetting agents/surfactants (e.g. Docusate) - The mechanism of action is that they reduce the surface tension on the stool which allows water and fats to penetrate stool - This softens the stool, making it easier to pass - Docusate also has some stimulant activity - Arachis oil and Paraffin are examples of stool softeners which work by creating a barrier between stool and intestinal wall - This eases the passage of stool through intestine - Paraffin no longer popular due to concerns over carcinogenicity

Answer 10

Children - Although there are laxatives licensed for children OTC, they require initial referral to a GP to have a physical examination. Red flags: - Pain on defecation - causing suppression of reflex - Patients over 40 years with sudden change in bowel habits (no obvious cause) - Greater than 14 days' duration (no obvious cause) - Associated fatigue - Presence failure of laxatives - Suspected laxative abuse

Answer 11

- Senna is a specific Anthraquinone laxative - Senna combines with sugars to form glycosides - Glycosides are molecules where the sugar is attached to a functional group via a glycosidic bond - In the gut the glycoside bond is hydrolysed by colonic bacteria to release irritant anthracene glycoside derivatives, specifically sennosides A and B - Sennosides A and B are absorbed and have direct action on the myenteric nerve plexus, increasing smooth muscle activity - Also postulated to increase PGE2 secretion (which increases gut motility) - Also reduce colonic water absorption which leads to a softer stool which is easier to pass.

Answer 12

- PAMORAs are competitive antagonist at intestinal mu-opiod receptors - They prevent opioid activation of intestinal mu-opiod receptors - They target underlying opioid induced side effects i.e. reduced GI motility - Hence resulting in normal propulsion and peristalsis