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PHARMACOLOGY FRCA > drugs acting on GIT + antiemetics + diuretics > Flashcards

drugs acting on GIT + antiemetics + diuretics Flashcards

1
Q

what drugs do you know that act on the GIT?

A

those that regulate acid
* ant acids
* H2 receptor antagonists
* PPI
* prostaglandins

those that regulate gastric emptying
* prokinetics
* slow gastric emptying - opioids

those that influence N&V
* emetic agents
* antiemetic agents

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2
Q

what are the roles of antacids? give examples

A

antacids work via neutralisation of stomach acid.
most commonly either Mg or alimium salts
e.g. Mg Carbonate or aliminium hydroxide.
also calcium carbonate.

these react with HCL to produce salts and CO2 and water.
relieve gastritis, protect ulceration

there is also sodium citrate often used in obsterics for emergency section.

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3
Q

common side effects of ant acids

A

magnesium = diarrrhoea
aliminum = constipation

can alter absorption of other compounds e.g. aspirin
belching due to CO2 production

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4
Q

which drugs act as mucosal protectors?

A

sucralfate
produces a physical barrier protecting mucosal layer.

no systemic effect, no change to pH or motility
however can reduce absorption of other drugs. e.g. warfarin.

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5
Q

what drugs act as prostaglandin analogues? side effects?

A

misoprostil = can be used to prevent ulcers by improving blood flow to mucosa and promoting mucus secretion

side effects include - increases uterine tone, diarrhoea, menorrhage

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6
Q

give examples of H2 antagonists and their mechanism

A

ranitidine, cimetidine , famotidine
competitive antagonism H2 receptors on parietal cells and preventing stimulation to acid release
hence reduces HCL production

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7
Q

what are the side effects of H2 antagonist?

A

cimetidine - CYP450 inhibitor, can cause bradycardia and hypotension, antiandrogenic (low sperm, gynacomastia)

ranitidine - link to gastric cancers so not used as much. can cause arrhtyhmias IV

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8
Q

give examples of PPIs and how they work?

A

omeprazole (20mg/40mg or IV 40mg), lanzoprazole (15mg/30mg), pantoprazole

work via irreversible inhibtion of H/K ATPase synthesis. leads to destruction of these proteins

increases pH
reduces gastric secreteions

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9
Q

describe the pharmacokinetics of PPIs..

A

omeprazole is a prodrug, activated within parietal cells.
hepatically metabolised and renal/bile excretion

lansoprazole, faster onset, better for severe cases

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10
Q

how does metaclopramide work?

A

normally a dopamine receptor antagonist for N&V
also
binds 5HT3 in gut on vagal afferent ending
increases stimulation of vagus nerve
release of Ach - increased motility, relaxed pylorus

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11
Q

which drugs affect gastric motility ?

A

prokinetics - erythromycin (motilin receptor), neostigmine (increased Ach), metoclopramide (5HT3 antagonist)

inhibition - opioids of u receptor in myenteric plexus. antimuscarinics (hyoscine, atropine)

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12
Q

how can antiemetics be classified?

A

by receptor mechanism
4 main NT involved in N&V= Acetylcholine, dopamine, histamine, serotonin
also substance P (neurokinin)

hence
5HT3 antagonist = ondansetron
H1 = cyclizine, promethazine
muscarinic receptor antagonist = hyoscine
dopamine antagonist = metaclopramide, domperidone , prochlorperizine

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13
Q

what are the uses of D2 recpetor antagonist?

A

mainly used as antipsychotics
but also in N&V

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14
Q

side effects of D2 antagonists antiemetics..

A

related to reduced dopamine
extrapyramidal effects = parkinsonism, occulogyric crisis, tardative dyskinesia, neuroleptic malignant syndrome
high prolactin - galactorrhoea, gynaecomastia

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15
Q

which D2 antagonist does not cause parkinsonism symptoms?

A

domperidone antiemetic that doesnt cross BBB so more favourable side effects.

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16
Q

what anti-emetics can be used in parkinsons

A

avoid D2 receptor antagonism
although can use domperidone - doesnt cross BBB

cyclizine or ondansetron can be used

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17
Q

describe a hollistic anti-emetic strategy…

A

prevention - identify those at risk, use TIVA, avoid N20 , avoid dehydration , opioid sparring

anti-emetics - ondansetron and dexamethasone pre op
technique - reduced gastric inflation , regional anaesthesia
post op - cyclizine, ondansetron as rescue , good pain management

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18
Q

which drugs act on the chemoreceptor trigger zone and nucleus tractus solitarus?

A

CTZ = D2, 5HT3
NTS = H1 and AchR

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19
Q

which antiemetics are used in kids

A

ondansetron, dexamethasone
avoid cyclizine esp under 6

20
Q

what are the features of neuroleptic malignant syndrome and how is it managed?

A

incidious onset from too little dopamine
rigidity, hyperthermia, confusion
sweating, tachycardia

stop treatment
bromocriptine / dantrolene / procyclidine
cooling

21
Q

how is occulogyric crisis treated?

A

procyclidine

22
Q

can you classify the diuretic agents..

A

can be classed by location they act

PCT - carbonic anhydrase inhibitors e.g. acetazolamide

LoH -
* osmotic diuretic (mannitol),
* loop diuretics (furosemide, bumetanide) - inhibit Na/K/Cl pump

DCT
* thiazides (indapamide, bendroflumethazide) - inhibit Na/Cl cotransporter
* ENaC - block Na rebsorption - amiloride - later in DCT

collecting duct
* aldosterone inhibitors - spironolactone , epleronone. inhibit synthesis of ENaC, Na/K ATPase, H/K. hence Na reabsorption

23
Q

what is mannitol?

A

polysaccrahide alcohol derivative that is not digested and thus acts osmotically within vasculature.

classed as an osmotic diuretic
180 daltons so freely filtered at kidneys, not reabsorbed, so draws water into tubules by osmosis.

in circulation also acts via osmosis e.g. across BBB to reduce oedema.
can also be used in bowel prep acting locally to draw water into the bowel when given enterally

due to its osmotic effects it also increases circulatory volume and so contraindicated in HF
cant be used if BBB is damaged or repeatedly as eventually crosses BBB whcih would result in worsening of oedema

dose 1g/kg

24
Q

how does acetazolamide work?

A

inhibits carbonic anhydrase in PCT
carbonic anhydrase is responsible for conversion of H20 and CO2 to H2CO3.
this normally produces H+ and HCO3 which are implicated in Na and Cl reabsorption

hence reduces NaCl reabsorption = diuresis
but also treats metabolic alkalosis by excreting HCO3

25
what are the uses of acetazolamide?
diuretic treatment of metabolic alkalosis or respiratory altitude e.g. altitude sickness glaucoma anti-epileptic
26
how do loop diuretics work?
inhibit Na/2Cl/K ATPase on TAL less of these reabsorbed less negative osmotic gradient created by loop of henle - less water can be reabsorbed. more ions excreted in filtrate
27
what are the indications for furosemide?
pulmonary oedema congestive cardiac failure promote diuresis in CKD/AKI other forms of fluid over load e.g. cirhosis and acites. treatment of hypercalcaemia
28
side effects of furosemide?
volume related - orthostatic hypotension, reduced GFR (may worsen AKI), reduced preload and CO. electrolyte - low K, low Ca, high Na CVS - also has mild vasodilatory effect - reduced SVR other = ototoxic
29
what are the pharmokinetics of furosemide like?
IV or oral -good BO minimally metabolised, mostly excreted renally un changed
30
how do diuretics effect levels of Na and K
lowers inhibits Na/Cl symptorter in early DCT so less Na reabsorbed more Na delivered to later tubules therefore drives Na/K ATPase hence more K excreted too
31
indications for thiazides?
diuretic - HF HTN hypercalcauria - reduces Ca excretion in urine
32
pharmacodynamics of thiazides
CVS - hypotension (less effective than loop), vasodilation renal - reduced GFR electrolyte - lowers Na, K, increases Ca , can precipitate gout and hyperglycaemia impotence, rash
33
how do thiazides and loop diuretics effect acid base balance?
loop - acidaemia thiazides - alkalosis
34
what is a thiazide like diuretic?
e.g. indapamide acts like thiazide but slightly different structure - no benzothiazide ring
35
how does spironolactone work? including pharamacodynamics
competitive aldosterone receptor inhibitor - intracellular receptor, alters gene expression reduced ENaC, Na/K ATPase, Na/H , K channels results in excretion of Na + hence water + hypotension reabsorption of K acidosis other - gynaecomastia
36
when is spironolactone used?
K+ sparing diuretic e.g. when K low and diuresis is required - liver disease conns syndrome
37
advantage of epleronone over spironolactone
fewer anti-androgen effects no gynaecomastia
38
what is amiloride?
ENaC channel inhibitor on distal DCT Na excreted because reabsorption inhibited less K excreted so increases K
39
what are the unwanted effects of acetazolamide?
can cause a metabolic acidosis
40
what are the other effects of mannitol (other than osmotic diuresis)
free radical scavenger - may protect brain against reperfusion release of renal prostaglandins - protects kidneys, improves blood flow
41
tell me about ondansetron..
commonly used anti emetic for preventive and treatment of N&V perioperatively and in medicine 5HT3 antagonist comes as clear colourless solution - 2mg/ml given as 4mg /8mg IV or orally and also IM TDS or dose of 0.1mg/kg in paediatrics pharmacodynamics - blocks 5HT3 peripherally and at vomitting centre - GI - constipation - long QT , bradycardia - neuro = flushing, headaches kinetics - oral, IM, IV - 60% BO . takes about 30mins to work. - large VD - hepatic metabolism, inactive metabolites - renally excreted - half life 3 hours
42
tell me about cyclizine
piparazine derivative commonly used antiemetic perioperatively and in community and other fields of medicine works via H1 antagonism comes as clear colourless solution of 50mg / ml. diluted up to 10ml of saline given as 50mg TDS (25mg in elderly) or 1mg/kg in children also as oral tablets - 50mg dynamics H1 receptor antagonisms mostly in vestibular apparatus and NTS so good for motion sickness also has some anti-muscarinic actions CVS - tachycardia, arrhythmias CNS - drowsiness, feeling of high when given too quickly GI - dry mouth kinetics - IV/ PO - good BO 80% - large Vd - liver and renal
43
how does aprepritant work?
neurokinin 1 receptor antagonist blocks substance P effects has a role in N&V relatively new class of antiemetic traditionally given in chemo
44
how does hyoscine work? side effects
hyoscine is a muscarinic antagonist (M3) 2 forms - hyoscine hydrobromide and hyoscocine butylbromide hyoscine hydrobromide = works in CNS (NTS and vestibular centre) as antiemetic. also has sedative effects and can cause hallucinations/ confusion. hyoscocine butylbromide = works periphrally at gut to prevent spasms = buscopan
45
tell me about dexamethasone
synthetic glucocorticoid used for N&V prevention, supression of inflammatory disease, CNS pathology (tumours), croup, covid pneumonitis and septic shock comes as clear colourless solution 3.3mg/ml. usually 6.6mg given IV (0.1mg/kg in children) can also be given orally pharmacodynamics - effects of steroids - GI - anti-emetic - metabolic - increases glucose (glycogenolysis, gluconeogenesis), lipolysis - CVS - fluid retention and Na retention, HTN - CNS - changes to mood and sleep, reduced oedema - long term - osteoporosis, muscle breakdown. - can cause peroneal burning if given IV caution in diabetics kinetics IV / oral - good BO large Vd hepatic and kidneys
46
what is metoclopramide?
antiemetic agent D2 antagonist (also with 5HT3 inhibition and Ach stimulation) also works as a prokinetic can be given orally or IV or IM given 10mg TDS pharmacodynamics GI - antiemetic, increased motility, increased LOS, reduced pylorus tone CNS - extrapyramidal endocrine - hyperprolactin
47
tell me about prochlorperazine
antiemetic and antipsychotic agent works via D2 antagonism can be given IM or IM side effect - extrapyramidal, hyperprolactin also long QT

PHARMACOLOGY FRCA (16 decks)

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