22. Lower GI Pharmacology Flashcards
What are the 4 disorders of the lower GI tract?
Diarrhea
Constipation
Irritation
Inflammation
What do we use to treat diarrhea?
One drug
Loperamide- has limited ability to cross BBB (minimal distribution to CNS)
Opioid agonists
Act on μ-receptors
Peristalsis
Side effects: constipation, arrhythmia (in high toxic doses)
Slides 5-8
What is constipation?
Subjective definition
Normal number of bowel movements will vary greatly between patients
Associated symptoms: straining, bloating
Severe constipation can result in serious complications, including perforations
Occurs for primary/idiopathic reasons and secondary reasons due to drugs that reduce peristalsis/GI secretions and disease
Drug induced causes: opioids, anticholinergics, diet, disease, old age
Slides 10-12
What are the 7 laxative sections used for constipation?
- Bulk
- Osmotic
- Stimulant
- Softeners
- Opioid antagonists
- Lubricants
- Other
What are the bulk laxatives?
One drug
Fibre (psyllium)
Fibre is part of food that is not broken down by digestive enzymes (remains intact in colon)
2 types: fermentable (bacteria act on it, increase mass of stool) and non fermentable (draws water into stool, increase mass of stool)
Increase bulk, increase peristalsis
Side effects: bloating and gas (high bacteria content), cramping can occur without hydration
Slides 14-17
What are osmotic laxatives?
2 examples
Sugars- polyethylene glycol (PEG)
Salts- magnesium hydroxide
Osmotic action (sugars or salts) in gut pulls H2O into colon (more potent than bulk)
Less likely to have issues with impaction
Side effects: diarrhea, bloating gas in sugar, electrolyte issues in salt
Slides 18-20
What are stimulant laxatives?
One drug
Sennosides
Directly stimulate the colon, increasing peristalsis
May induce a temporary inflammatory response, which promotes secretion of fluid (irritant laxatives)
Side effects:
Diarrhea
Cramping
Slides 22-23
What are softener laxatives?
One drug
Docusate
Act as detergents, breaking down surface tension between lipids/water in stool
Enhances penetration of water into stool
The emollient action causes stoops to lose their form, this reduces the ability of the feces to stimulate the colon (all mush no push)
Side effects: mild GI side effects (cramping, nausea)
Slides 25-27
What are the opioid antagonist laxatives?
One drug
Methylnaltrexone
Mu antagonist
Polar, so doesn’t cross into CNS
Blocks peripheral opioid receptors (no analgesic response to opioids
Side effects: diarrhea, nausea, cramps
Slides 29-30
What are the lubricant laxatives?
One drug
Mineral oil (heavy)
Lubricates the colon, facilitates passage of stool
Oral or rectal
Light mineral oil used for skin conditions
Side effects: concern of aspiration when given orally (lipid pneumonia)
Slides 32-33
How are serotonin (5HT-4) agonists used as laxatives?
One drug
Prucalopride
Stims 5HT-4 receptors results in release of ACh, which stims GI peristalsis
Highly selective
Side effects: safer than non selective drugs, lack cardiovascular side effects
Slides 35-36
How are cGMP agonists used as laxatives?
One drug
Linaclotide
Increases intestinal secretions
Reduces transmission of pain signals
Side effects: diarrhea
Slides 37-38
What other 2 drugs stimulate peristalsis?
Motilin agonists- erythromycin
Cholinergics
