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D4: Regulation of pH in stomach : :warning: (Specific reactions…
D4: Regulation of pH in stomach : :warning:
Specific reactions
Ranitidine (Zantac)
How does it inhibit production of HCl?
Drug binds to H2 receptor protein in membrane of parietal cells
Once it is binded, histamine cant bind to the H2 receptor protein
Because histamine cannot bind to receptor on parietal cell, it stops chain of events that produce H+.
Thus, no H+ is pumped to stomach lumen, thus no HCl is produced.
H2-receptor antagonist because it stops the naturally occuring molecule (histamine) to bind to the H2 receptor protein.
Ranitidine
Omeprazole (Prilosec) and Osemaprazole (Nexium)
How does it suppress acid secretion in stomach?
The drug is basic and mostly un-ionised in blood plasma and non polar so it is lipid soluable.
Once inside the parietal cell the basic molecule will be protonated (forms bond with H+) because the inside of cell is more acidic.
Protonation starts a series of reactions--> alter drug so it can irreversibly bind to PP.
PP cannot pump H+ into stomach lumen, suppressing acid production.
Works until cell can produce new PP.
Osemaprazole (consist mostly of one enantiomer)
Omeprazole (racemic mixture)
How is HCl produced in stomach?
Water and carbon dioxide is reacted in parietal cell (in gastric gland) --> carbonic acid
Carbonic acid is weak acid and dissociates to H+ and C03-
H+ is pumped into by PP stomach lumen where it reacts with Cl-
Non-specific: do not bind to protein receptors
Common antacids used:
Bases
carbonates and hydrogencarbonates (bicarbonates)
magnesium hydroxide
aluminium hydroxide
calcium carbonate
sodium hydrogencarbonate (also called sodium bicarbonate).
A(OH)(s) + HCl(aq) > A(Cl)(aq) + H2O(l)
A(CO3)(s) + HCl(aq) > A(Cl)(aq) + H2O(l) + CO2(g)
metal hydroxides
Usually combined:
Magnesium and Aluminium
-Magnesium can cause laxative effects
-Aluminum can induce constipation
Note:Magnesium react faster than Aluminium
Antacids- neutralize excess acids in stomach
Alginates & Anti foaming agents:
Aliginates float on the stomach contents
neutralizing layer prevent reflux of stomach acids
Anti-foaming agents : prevents formation of gases & reduce flatulence
simethicone
dimethicone
Antacids often combined with Alginates & anti-foaming agnets
Excess acid can causes: :fire:
Indigestion: irritation of the stomach lining
Heartburn (acid reflux): acid from the stomach rising up into the esophagus causing a burning sensation
Peptic ulcer:erosion of part of the gut lining
Buffer
active metabolites
Why are drugs created not in active form?
To allow drug to pass through cell membrane more easily. Example: Codeine. Active form is morphine but ingested in the form of Codeine so the drug can pass through brain blood barrier easier.
To void side effects
Example is aspirin. Its active form is salicylic acid but is ingested in the form of acetylsalicylic acid to avoid discomfort in the stomach
To allow the drug to be more water soluble-
Example: Fosphenytoin (epilepsy drug) which is more water soluble than its active ingredient phenytoin.
To target specific areas in body
. Example omeprazole is only in its active form in acidic solutions. Thus, it can target the parietal cells in the lining of gastric glands.
