GI: Drugs used in Diarrhoea and Constipation Flashcards
What are the causes of diarrhoea?
Infection chronic disease toxins drugs psychological
What are the consequences of diarrhoea?
Dehydration, metabolic acidosis and hypokalaemia
What is the first priotrity in diarrhoea treatment?
Maintainance of fluid and electrolyte balance
What can cause impared sodium chloride reabsorption?
Congential
inflammation
infections
excess bile acid in colon
What other causes of diarrhoe are there
Lactase deficientcy resulting in poor absoption
hypermotility
excessive secretion
Describe excessive secretion diarrhoea?
Cholera is an example
Cholera toxin enters enterocyte and inhibits GTPase activity of the Gs alpha subunit
Increased activity of adenylate cyclase
increased cAMP which stimulates CFTR
hypersecretion of Cl with Na and water following= DIARRHOEA
What receptro is exploited in rehyrdation therapy?
SGLT1
What is contained in typical rehydration salts?
Glucose
Sodium chloride
sodium bicarbonate
potassium chlorise
What is the mechanism of action of rehydration therapy?
Absorption of sodium and glucose by SGLT1 causes accompanying absoption of water
Describe exactly how rehydration therapy works?
two sodium bind to SGLT1
affinity for glucose increases and glucose binds
sodium and glucose translocated from extracellular to intracellular
two sodium dissocite
decrease glucose affintiy
glucose dissociates
cycle repeats
Name anti motility agents used in diarrhoea?
Codeine
diphenoxylate
Loperamide
What is the action of opiates on the GI tract?
inhibition of enteric neurones (hyperpolarization via activation of -opioid receptors)
decreased peristalis, increased segmentation (i.e. constipating)
increased fluid absorption
constriction of pyloric, ileocolic and anal sphincters
What do purgatives do?
increase peristalsis and/or soften faeces causing, or assisting, evacuation
When are purgatives used?
when ‘straining’ is potentially damaging to health (e.g. patients with angina), or when defaecation is painful (e.g. haemorrhoids) predisposing to constipation
to clear bowel before surgery/endoscopy
to treat drug induced constipation or constipation in bed ridden /elderlt patients
Name a bulk laxative
Methycellulose- orally - retain H2O- increase volume
