MP322 week 7 Flashcards
diarrhoea
increased liquidity of still and or increased loose/ liquidity stool frequency
classification
- acute 14 days or less
- persistent more than 14 days
- chronic more than 30 days
2 main pathophysiological categories of diarrhoea
inflammatory and non inflammatory
inflammatory diarrhoea
- presence of an inflammatory process (can be due to viral, bacteria or parasitic infection), radiation injury, or inflammatory bowel disease
- mucoid and bloody stool, temesmus, fever, cramps abdominal pain
- small, frequent bowel movements
- histology of GI tract is abnormal
non-inflammatory diarrhoea
- watery, large-volume, frequent stool (10, 20 per day)
- volume depletion is possible die to high volume and frequency of bowel movements
- no tenesmus, blood in the stool, fever, or faecal leucocytes
- histology of GI tract is preserved
non inflammatory: osmotic diarrhoea
- presence of unabsorbed or poorly absorbed slate (eg Mg2+, mannitol)
- stool volume is small (compared to secretory diarrhoea)
- stops or improves with fasting
- due to maldigestion or malabsorption
non inflammatory: secretory diarrhoea
- altered transport of ions across the mucosa
- increased secretion and decreased absorption of fluids
- doesn’t improve with fasting
aetiology: infectious
- most common cause of acute diarrhoea
- bacteria
– E.coli, campylobacter, salmonella, clostridium difficle, listeria, vibrio cholerae - viruses
– rotavirus, noravirus, adenovirus, astrovirus - parasites/ protozoa
– entamoeba hisolitca, girardia lablia, cryptosporidium
aetiology: non infectious
- most common cause is medication
- cardiovascular drugs
– digoxin, quinidine, propranolol, ACE inhibitors - GI drugs
– antacids (magnesium salts), laxatives, H2 antagonists - endocrine system drugs
– oral hypoglycaemic agents, thyroxine
-antibacterials
– amoxicillin, cephalosporins, erythromycin
physiology of diarrhoea
water follows the movement of electrolytes (Na+, K+, cl-, water) and glucose
due to different concentrations of solutes and water, the water is moved by osmosis
epithelial cells are polarised- meaning the membrane on one side of the cell has different transport systems than the other
membrane that faces GI lumen, is the apical membrane and membrane that faces interstitial side is called basolateral membrane
therefore the reabsorption of water requires prior movement of solute to create an osmotic gradient (water will always follow movement of electrolytes for this reason)
mechanisms causing diarrhoea
- increased secretion of liquid in the GI tract
- decreased absorption into the blood
absorption of water is passive and is secondary to the absorption of solutes
- increased cl- secretion
- reduced Na+ absorption
- increased paracellular permeability
- reduced Cl- absorption
- reduced H2O absorption
- reduced Na+ and glucose absorption
Cl- transport in the intestine
- secreted Cl- is provided by the Na+/K=/2Cl- co-transporter
- activity is driven by low intracellular Na+
- Cl- is secreted through Cl- channels
- Na+ and water enter lumen by paracellular transport (also transcellular for water)
- paraceullular- diffusion between epithelial cells
- this is limited by tight junctions between epithelial cells
- water can use aquaporins to pass into the cell and then pass out again to the other side
infection - vibrio cholerae
- cholera toxin from vibrio cholerae enter cells
- activates G protein, which is coupled to and activates adenylyl cyclase (enzyme which converts ATP to cyclic AMP)
- increases cellular cAMP and activation of protein kinase A (PKA)
- phosphorylation of Cl- channel
- increased efflux of Cl- (and water)
- water and sodium ions are drawn into the lumen
- diarrhoea
use of antibacterials (in diarrhoea)
- disruption of normal intestinal microflora
- proliferation of opportunistic pathogens ( eg C. diff- produced 2 toxins)
- impaired fermentation of poorly absorbed carbohydrate and/ or reduced production of short chain fatty acids
increased motility
- reduction in intestinal transit time will result in inadequate absorption
- drugs with cholinergic activity (eg pilocarpine- for dry mouth)
- drugs with anti cholinesterase activity (eg donepezil for Alzheimer’s disease)
drug treatment of diarrhoea
- anti motility drugs
- prolong the duration of intestinal transit
- uncomplicated acute diarrhoea in adults
diphenoxylate
- u (mu) opioid receptors on neuronal varicosities
- myenteric plexus
- activation pf opioid receptors decreases ACh release
- peristaltic activity is decreased
- increased segmental contraction
- diphenoxylate is usually provided as a mixture with atropine (co-phenotrope)
codeine phosphate
- symptomatic relief of chronic diarrhoea
- POM
- mechanism of action similar to that of diphenoxylate
adverse effects of opiates
- rebound constipation
- higher doses can have CNS effects
- prolonged use can lead to opioid dependence
racecadotril
- activation of delta opioid receptors decreases the cellular cAMP level
- decreased secretion of Cl-
- decreased water secretion
- enkephalins are the endogenous activator of delta opioid receptors
- racecadotril (pro-drug) metabolised to thiorphan
- thiorphan is an enkephalinase inhbitor (prevents the breakdown of enkephalins)
constipation
- heterogeneous disorder
- patietnts report one or more of these symptoms
– fewer than 3 bowel movements per week
– straining
– lumpy or hard stools
– sensation of anorectal obstruction
– sensation of incomplete defaecation
– manual manoeuvring required to defaecate
common causes of constipation
primary
- normal - transit constipation
- slow transit constipation (colonic inertia)
- pelvic floor dysfunction
- irritable bowel syndrome with constipation
secondary
- medications
- metabolic disorders
- endocrine disorders
- psychiatric (anxiety, depression)
mechanisms of drug- induced constipation
- drugs with anticholinergic activity (eg antidepressants, antihistamines, antimuscarinics, antipsychotics, antiparkinsonian agents)
- opioids
- drugs affecting electrolytes
- laxative misuse (leads to atonic colon)
treatment of constipation
laxatives
- osmotic
- stimulant
- bulk-forming
- faecal softeners
drug treatment
- predominantly used in constipation associated with IBS and chronic idiopathic constipation
linaclotide
- 14 amino acid synthetic peptide
- linaclotide activates guanylate cyclase C (GC-C)
- increases cellular cGMP and activation of protein kinase G (PKG)
- phosphorylation of Cl- channel
- increased efflux of Cl- and water
- restricted use (SMC)
lubiprostone
- member of a class of agents called prostones
- derived from functional fatty acids that occur naturally
- lubiprisone directly activates a Cl- channel (CIC-2)
- increase efflux of Cl- and water
- may restore mucosal barrier function
adverse effects of linaclotide and lubiprostone
- generally well tolerated
- diarrhoea
- nausea
- vomiting
- abdominal pain
treatment of GIT inflammation
- carboxylic acids are converted to sodium salts
- the di-sodium salt is more water soluble and therefore dissolves faster
mechanism of action of salfalazine
- its a pro drug
- breakdown to the active 5-aminosalisilic acid (5-ASA)
- site of action is the colon
- mechanism of action is not clear but possibly inhibits prostaglandin and leukotriene biosynthesis amongst others
delivery and absorption of sulfalazine in the colon
- delivery and absorption is mainly at the colon
- due to bacterial induced cleavage of sulfalazine to the active 5-ASA
- the resulting sulfapryidine has no anti-inflammation effect
- but some side effects arise from sulfapyridine hence why balsalazide and olsalazine designed
- the colonic microflora contain many species of bacteria
- low in oxygen and pH (6-7)
- gives rise to reductive environment
- bacterial ago-reductases cleave sulfalazine ago bond to give 5-ASA (more lipophilic)
administration and formulation
- structure and environment of colon dictate its use
- administration as oral coated tablet disintegrating at pH 7 in the intestine or suspension
- administration by rectum in suppositories or enema
pKa rule of 2
for base
- pH 2 above pKa =100% ionised
- pH 2 below pKa = 100% unionised
for acid
- pH 2 above pKa= 100% unionised
- pH 2 below pKa= 100% ionised
absorption of sulfalazine
- log P = 3, OH, COOH and SO2NH are not ionised
- pyridine is fully ionised at pH in stomach
- log D=0, no absorption across stomach membrane
- the drug travels to the small intestine
- sulphonamides are weakly acidic
- SO2NH dissociation and OH and pyridine no ionised
- COOH is fully ionised and so molecule not absorbed
- molecule is large and so it passes through to the colon where it gets cleaved to 5-ASA
- OH, SO2NH, pyridine not fully ionised
- COOH is fully ionised at pH=7 and it not absorbed passively
- but the molecule is then cleaved by gut flora to 5-ASA
absorption of mesalazine
- OH and NH2 not ionised
- COOH if fully ionised at pH 7 so no passive diffusion
- but it may absorb through aqueous gaps in between epithelial cells as it is a small, polar molecule
delivery of drugs to the colon
delivery is directed to the colon via MR tablets/ capsules, granules, suspensions or foam, suppository or enema
active form of sulfalazine
active form is 5-ASA or mesalazine (hydrophilic)
breakdown to the active form is done by gut flora
what are steroids
- hormone molecules which control many biological events
- sex hormones, inflammation, immunomodulation, stress
- they are all derived from lanosterol in animals
- produced in adrenal glands
- glucorticosteroids (corticosteroids) are important in controlling inflammation
- all share same 4 membered ring structure backbone
steroid backbone structure
- organic 4 ring containing compounds
- A, B, C = 6 membered ring
- D= 5 membered ring
- with hydroxyl groups known as sterols
- no aromatic
- aliphatic- is what gives 3D space
hydrocortisone (cortisol)
- hydroxyl groups - aliphatic
- carbonyl groups
- won’t go into dissociation equilibrium at physiological pH
beclometasone
- extra bond on A ring
- added chlorine (will increase lipophilicity)
- extra methyl group
budesonide
- long carbon tail - increases lipophilicity