Pharmacology of Fluid Motility Flashcards
causes of travellers diarrhoea
Enterotoxin producing E coli
also salmonela, shigella and campylobacteria
the most common strain of bacteria causing gasstroenteritis in the UK is
Campylobacter jejuni
non infectious causes of diarrhoea
IBS. IBD, bile salts excess and lactase deficiency
physiological factos eg anxiety
hyperthryoidism
drug induced - Mg salts, beta blockers, cytotoxic drugs
goals in management of diarrhoea
maintain fluid and electrolyte balance
antimicrobial agents in sever infective causes
antimotility and spasmolytic agents - symptomatic
rehydration in diarrhoea when fluid loss is severe
IV rehydration
rehydration in diarrhoea normally
ORT - Restore & maintain hydration till diarrhoea ceases (spontaneously)
which transporter does rehydration therapy exploit
SGLT1 - absorption of Na and glucose by SGLT1 cause accompanying absorption of water
what type of relief do anti motility agents give
symptomatic
what are anti motility agents contraindicated in
acute infective diarrhoea, IBS, IBD, diverticulosis
examples of anti motility agents
opiates
- loperamide
- Diphenoxylate
- codeine
what negative effect do opioid drugs have
constipating
effects of opioid drugs
activate μ-receptors on myenteric neurones and cause hyperpolarization by increasing their potassium conductance.This inhibits acetylcholine release from the myenteric plexus and reduces bowel motility.
dec peristalsis, inc segmentation
inc fluid absorption
inc tone of large intestine
benefits of loperamide
weak antimuscarinic effect
longer acting
best for local effect on gut as has little effect on the brain
therefore unlikely to cause dependence
diphenoxylate
low CNS penetration
can contain atropine - discourage drug abuse due to side effects e.g. nausea, vomiting, blurred vision, headache, weakness
and atropine is used in cardio for
bradycardia
antidiarrhoeal agent examples
Racecadotril
what is Racecadotril a pro drug of
thiorphan
what is a pro drug
A prodrug is a medication or compound that, after administration, is metabolized into a pharmacologically active drug.
how does one use Racecadotril
in children over 3 months of age as an adjunct to rehydration
what are loperamide or diphenoxylate contraindicated in
children
what does Racecadotril inhibit
enkephalinase inhibitor - inhibits the breakdown of endogenous opioids & reduces intestinal secretions.
what can the Hirschprung disease cause
impairment of motility/defaecation reflex e.g. constipation
compare laxative and purgative action
laxative produce a midler action resulting in passage of soft but formed stools
purgative produce a stronger action resulting in more fluid evacuation
can the same drug act as laxatives and purgatives at different doses
yes - laxative at low, and purgative at high
contraindications of laxatives and purgatives
physical obstruction in the bowel
reasons of laxative dependency
- easily resorted to as OTC
- abused in eating disorders
abuse of laxatives may result in what
hypokalaemia
what does hypokalaemia do to you
make you tired or act as a stimulus for cardiac arrhythmias
bulk laxative example
methycellulose
bulk laxatives
inc volume of intestinal contents causing peristalsis
are indigestible polysaccharides
osmotic laxatives mechanisms and examples
inc bulk in bowel by retaining water by an osmotic effect
Mg sulphate or hydroxide
sodium citrate
lactulose
Mg sulphate or hydroxide administration route
and lactulose
oral
sodium citrate administration route
rectal
stimulant purgatives examples
bisacodyl- orally or suppository
senna
sodium picosulfate
name an anthraquinone laxative
senna
faecal softeners examples
softeners - docusate sodium - oral
lubricants - archis - oil as enema
oral liquid paraffin
which class of laxatives are abdominal cramps less common with
stimulant purgatives
what is diarrhoea defined as
loss of fluid and solutes from the GI tract in excess of 500ml per day
how does rotavrus cause diarrhoea
inhibition of Na/K/ATPase & structural damage to mucosal cells leading to reduced absorption
stimulant laxative mechanism
inc motility by actin g on mucosa/nerve plexuses, which may be damaged due to prolonged drug use
faecal softeners
promote defecation by softening or lubricating the stool