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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
Q

what are the uses of acetazolamide?

A

diuretic
treatment of metabolic alkalosis
or respiratory altitude e.g. altitude sickness
glaucoma
anti-epileptic

26
Q

how do loop diuretics work?

A

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
Q

what are the indications for furosemide?

A

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
Q

side effects of furosemide?

A

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
Q

what are the pharmokinetics of furosemide like?

A

IV or oral
-good BO
minimally metabolised, mostly excreted renally un changed

30
Q

how do diuretics effect levels of Na and K

A

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
Q

indications for thiazides?

A

diuretic - HF
HTN
hypercalcauria - reduces Ca excretion in urine

32
Q

pharmacodynamics of thiazides

A

CVS - hypotension (less effective than loop), vasodilation
renal - reduced GFR
electrolyte - lowers Na, K, increases Ca ,

can precipitate gout and hyperglycaemia
impotence, rash

33
Q

how do thiazides and loop diuretics effect acid base balance?

A

loop - acidaemia
thiazides - alkalosis

34
Q

what is a thiazide like diuretic?

A

e.g. indapamide
acts like thiazide
but slightly different structure - no benzothiazide ring

35
Q

how does spironolactone work? including pharamacodynamics

A

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
Q

when is spironolactone used?

A

K+ sparing diuretic e.g. when K low and diuresis is required - liver disease

conns syndrome

37
Q

advantage of epleronone over spironolactone

A

fewer anti-androgen effects
no gynaecomastia

38
Q

what is amiloride?

A

ENaC channel inhibitor
on distal DCT

Na excreted because reabsorption inhibited
less K excreted so increases K

39
Q

what are the unwanted effects of acetazolamide?

A

can cause a metabolic acidosis

40
Q

what are the other effects of mannitol (other than osmotic diuresis)

A

free radical scavenger - may protect brain against reperfusion

release of renal prostaglandins - protects kidneys, improves blood flow

41
Q

tell me about ondansetron..

A

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
Q

tell me about cyclizine

A

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
Q

how does aprepritant work?

A

neurokinin 1 receptor antagonist
blocks substance P effects
has a role in N&V

relatively new class of antiemetic
traditionally given in chemo

44
Q

how does hyoscine work? side effects

A

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
Q

tell me about dexamethasone

A

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
Q

what is metoclopramide?

A

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
Q

tell me about prochlorperazine

A

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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