1. systemic (bioavailable): bicarb. 2. nonsystemic (poorly absorbed): Ca, Mg, Al

Feb22 M3-Antacids and prokinetic drugs Flashcards by Django E.

ulcers cause+consequence and therapeutic goal

cause: bacterial infections
consequence: higher acidity in stomach
goal: stop excessive acid in stomach

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direct way of reducing stomach acid

PPI blocks H (out) K (in) ATPase on luminal surface of parietal cell

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4 receptors on parietal cell basal side regulating HCl secretion + effect

M3 (muscarinic R): activates Ca dep pathway to release more HCl
gastrin R (Ca dep pathway too)
histamine R (activates cAMP dep pathway to release more HCl)
PG R (blocks Ca dep pathway)

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drugs acting indirectly on parietal cell to reduce acid secretion and one acting to increase it

musc antag
CCK2 (gastrin) R antag
histamine R antag
NSAIDs increase it

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direct way of neutralizing stomach acid

bases (chemistry). many drugs like that

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final problem of stomach acidity (why block it)

acid activates pepsin. overtime destroys wall of stomach = ulcers

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drug blocking stomach wall

sucralfate (helps mucous layer)

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how to tackle main cause of peptic ulcer

Abx (bacterial infection): bismuch, metro, tetracycline

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(imp?) 5 drugs used for ULCER therapy

antacids to neutralize
cimetidine (H2i)
propantheline (M1 M3 blocker)
adenylate cyclase blockers (cAMP = histamine pathway)
PPI

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problems with cimetidine + alternative

ranitidine (better H2i). less anti-androgenic effects, longer action, no drug interaction (no p450 interaction)

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omeprazole (PPI) advantages (2)

activated when needed only (more acid in stomach = activated more)
forms disulfide bridge with the pump and changes its chemistry = acts longer

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omeprazole side effects

gastric mucosa hyperplasia (to compensate): may lead to gastric CA (hyperplasia stim by gastrin release in response to high pH)

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2 kinds of antacids

systemic (bioavailable): bicarb.

2. nonsystemic (poorly absorbed): Ca, Mg, Al

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systemic antacids side effect

alkaline blood

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what makes antacids diff from one another

onset time, duration of action, constipation or laxative effect

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4 kinds of antacids + how to choose

-Na and K
-Ca
-Mg
-Al
choose depending on medical condition

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long and short acting antacids

long = Ca and Mg
short = Na, K

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sucralfate (mucosa protecting drug) mech of action

complexes with proteins on ulcer side to provide coating for mucosa (+ binds to pepsin)

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gastroparesis def + condition where cna happen

damage to gastric nerves or SM (ex, diabetes) = more acidity in stomach bc delayed gastric emptying

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workforce to drive GI tract is why

Ach innervation to SM (Ach on musc Rs)

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prokinetic drugs acting in synaptic cleft

M3 agonists (bethanechol)
AChEi (neostigmine)

prokinetic drugs acting downstream on the presynpatic neuron

D2R inhibitors (dopamine) (metoclopramide) so the negative effect of this pathway on Ach release is blocked

prokinetic drugs acting upstream on neuron presynaptic

erythromycin (motilin R bindors): positive regul of firing

- serotonin R agonists (cisapride) positive effect on firing

bethanecol (musc agonist) side effect and prob

non specific .. heart relaxation (M2)

cholinergic drugs (bethanecol and neostigmine: M agonists and AChEi) side effects

stim GI secretions (acid included) (not just mvmt), reflex and asthma are problematic and exacerbated by them and heart prob too.

classical D2Ri drug and one more used now

metoclopramide. (acts on CNS so not too good) domperidone better

D2Ri drugs other effect (benefits that it's non specific)

blocks emesis, more GI coordination, etc.

D2Ri side effects

increase prolactin and breast tenderness (gynecomastia, galactorhea, etc.)

serotonin agonist used upstream on neuron (prokinetic)

metoclopromide (also D2 antagonist) and it has a mixed 5HT4 agonist, 5HT3 antag effect

why cisapride not used as serotonin $ agoist

activates arrhythmia channel in the heart. can cause death + galactorrhea + extrapyr effects in the brain

5HT4 R signal transduction

GPCR activates cAMP, higher Ca in the cell

5HT4 R agonist side effects and why

-more stim of bladder (R is on SM too) and adrenals

good thing in cisapride and metoclopromide

block 5HT3 (and also D2 for metoclopromide) in CTZ = block emesis

serotonin agonists effects on GI tract

- more gastric contractions - more gastroduod coordination - lower sphincter in stomach contracts more

motilin R agonists (erythromycin) effect on GI tract

more LES contraction, GI contraction

paresis meaning

lack of GI movement

most important factor in how food moves down GI tract

how liquid the food is

constipation 3 causes

- functional disorders (damage to enteric nerves or muscles) - drug treatments (opiates) - low residue diet (residue = attracts water)

5 types of laxatives (SSELB)

- secretory or stimulant - saline - emollient - lubricant - bulk forming

principle of laxatives

goal is to activate Cl channels in GI tract (their pumping of Cl in lumen is what keeps water in lumen)

secretory laxatives (castor oil) mech (2)

1. activate the PG receptor EP3 (Cl channels more active) | 2. inhib water reabso in lower intestine

secretory laxative used in IBS and opioid induced constipation

lubiprostone

saline laxatives mech + examples

draw water in intestine by osmosis (Mg hydroxide, sodium phosphate, sodium sulfate)

emollient laxatives mech

attract water to stool (anionic surfactants. lower surface tension of stool) EX: DOCUSATE

lubricant laxatives mech + ex

retard water abso, smooth transit, less transit TIME (faster velocity) ex: mineral oil

bulk forming agents laxatives mech + example

form large hydrophilic masses (less viscosity of content + more bulk and water content) Ex: Bran (fibres) OR psyllium husk

4 problems of laxatives

- damage to myenteric plexus + habituation (bc ENS used to working less) - colonic atony - too much Ca loss

order of things to do when need laxatives

- increase diet fibers and water - bulk agents - osmotic laxatives - stimulants (secretory): more pharma ones are last resort

antidiarrheal drugs mech of action

act on intestinal neurons: more abso, less fluid secretion, more segmental contractions, less propulsive contractions + act on CNS

ex of antidiarrheals

opioids, morphine, codeine

morphine and codeine good and bad

good: segmental contractions more and propulsive less bad: act on CNS... (crosses BBB) SO ARE NOT USED for diarrhea in enteric infections

drugs used as antidiarrheal and why

loperamide and diphenoxylate (no CNS effects)