chemistry of drugs acting in the stomach Flashcards
why shouldn’t you use sodium hydroxide as a treatment to neutralise stomach acid
it is extremely caustic - severe damage to the oral cavity, oesophagus, stomach and small intestine
how does using milder alkaline materials eg sodium bicarbonate work to neutralise stomach acid
used as a buffer to maintain plasma pH
risk of alkalosis
production of CO2 can lead to bloating of stomach
how does using milder alkaline materials (that don’t release gases) work to neutralise stomach acid
they combine with alginates - polymers which expand on wetting in the presence of multivalent cations
form rafts in stomach that reduce acid reflux
what are alginates
polymers of sugars, the calcium in the formulation binds with the alginates and they start to aggregate
what do parietal cell proteins do
they exchange K+ for H+ by hydrolysing ATP and pump acid into the stomach
what activates proton pumps
acetylcholine, histamine and gastrin at their respective receptors
disadvantages of drugs which block the muscarinic acetyl cholinergic receptors
drugs administered systemically will go everywhere, won’t just act at muscarinic receptors in the parietal cells
where are muscarinic receptors found
throughout the parasympathetic nervous system and involved in cardiac and respiratory control
how does histamine increase acid secretion
by stimulating the parietal proton pumps into action
why do regular antihistamines not work to reduce acid production
there is more than one type of histamine receptor in the stomach
what are agonists
small and flexible with similar functionality to the natural ligand
issues with metiamide (1st H2 agonist)
thiourea group had issues, produced poor physiochemical characteristics and was associated with toxicity
issues with 2nd H2 agonist
thiourea group changed to a guanidine group and pka so high that the drug was never ionised and so poorly absorbed
issues with third H2 agonist (cimetidine)
worked fine but had to be took 3 times a day, not good with patient compliance
