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BVetMed3 POS - Pharmacology > SA GI Drugs > Flashcards

SA GI Drugs Flashcards

1
Q

What is the goal of antiemetic therapy?

Why should it be used with caution

A

As a symptomatic therapy - treating the clinical signs, not the underlying problem.

COULD MASK A SERIOUS PROBLEM

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2
Q

What receptors associated with eyes is are found in the nucleus tractus solitarius?

A

NK1

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3
Q

Where are serotonin receptors found in relation to emesis?

A

Vomiting centre in the medulla,

Chemoreceptor trigger zone

Vomiting centre

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4
Q

What are the classes of antiemetic drugs?

A 
NK1 antagonists 
Metaclopramide 
Phenothiazines
Antihistamines (motion sickness)
Serotonin antagonists
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5
Q

Where are H1 and H2 histamine receptors found in relation to emesis?

A

The CRTZ

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6
Q

What is the most effective vet licensed anti-emetic for dogs and cats?

A

Maropitant (Cerenia)

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7
Q

How does maropitant work?

A

NK1 receptor antagonist
Inhibits nucleus tractus solitarius

Therefore inhibits final common pathway involved in activating the vomiting reflex in the CNS.
Effective against emesis induced by both peripheral and central stimuli

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8
Q

In what clinical context may maropitant be used?

A

Acute gastroenteritis
Cytotoxic-induced vomiting
Motion sickness (higher dose required)

Also:
Pancreatitis, liver disease etc which will RESOLVE

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9
Q

What is a limitation of maropitant?

Why?

A

Effective antiemetic BUT

NOT VERY EFFECTIVE ANTI-NAUSEA DRUG

Nausea has a different mechanism - therefore animal will stop vomiting but my still not want to eat

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10
Q

What is the ligand for the NK1 receptor?

A

Substance P

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11
Q

Why are the oral and injectable doses of maropitant different?

A

Oral dose is much higher than injectable dose due to significant first pass metabolism in LIVER

This reduces the amount of blood that reaches the blood stream.

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12
Q

When should you NOT give maropitant?

A

If GI obstruction is suspected

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13
Q

What would you do if vomiting returned after the first course of maropitant?

A

INVESTIGATE THE CAUSE

Don’t repeat unless you know what is causing the vomiting

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14
Q

Where are D2 receptors found in relation to emesis?

A

The chemoreceptor tigger zone

Peripheral receptors

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15
Q

How does metaclopramide work?

A

Antagonises d2 dopaminergic receptors
Antagonises serotonin receptors

Has a peripheral PRO-cholinergic effect

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16
Q

How can the peripheral pro cholinergic effect of metoclopramide be beneficial?

A

Increases GIT motility

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17
Q

When is metoclopramide indicated?

A

Various emesis inducing disorders which involve central or peripheral activation of vomiting

Cancer chemotherapy
Gastroesophageal Reflux
Decreased gastric emptying

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18
Q

When might you choose metaclopramide over maropitant ?

A

Where a patient has decreased gut motility

When there is decreased gastric emptying

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19
Q

What could cause decreased gastric emptying?

A 
Inflammatory GI disorders
gastric ulcers 
gastric neoplasia 
Autonomic neuropathy (diabetes mellitus)
Pyloric stenosis(thickening)
Postoperative gastric volvulus patient 
Hypokalaemia 
Abnormal gastric motility
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20
Q

Where are alpha adrenergic receptors found in relation to emesis?

A

The vomiting centre in the medulla

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21
Q

Where are muscarinic cholinergic receptors found in relation to emesis?

A

In the vestibular system

CRTZ

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22
Q

How do Phenothiazines act?

A

Antagonists of:

alpha 1+2 adrenergic receptors
D2 dopaminergic receptors
H1 and H2 histaminergic receptors
Muscarinic cholinergic receptors

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23
Q

What ‘areas’ of emesis do phenothiazines effect?

A 
Vestibular system (M2)
Vomiting centre (a2)
CRTZ (D2,M1, H1+2)
Peripheral receptors (D2)
24
Q

What are phenothiazines indicated for?

Why might another drug be favoured?

A

Any central or peripheral cause of vomiting

NOT licensed for veterinary use in the UK

25
Q

What MUST you do when giving off label drugs to patients?

A

Get informed consent from owner

26
Q

Are antihistamines effective for all small animals?

Why?

A

Antihistamines effective for DOGS not cats.

Histamine receptors in CRTZ involved in motion sickness in dogs

27
Q

What are the most effective anti-emetic and anti-nausea drugs?

A

Serotonin antagonists

E.g. Dolasetron and ondansatron (Zofran)

Efficacy as antiemetic orders of magnitude above metaclopramide !!!!!

28
Q

When are serotonin antagonists indicated?

A

To control cytotoxic drug induced emesis (chemo e.g. cisplatin)

29
Q

What is the typical combination/progression of antiemetics in practice?

A

Usually start with maropitant then progress onto ODANSATRON (serotonin antagonist)

30
Q

Why are anti cholinergics NOT used as antiemetics?

A

affect peripheral M2 receptors resulting in potential for delayed gastric emptying and ileus

31
Q

Why would anti cholinergics be effective against motion sickness (even though there would be side effects)?

A

Antagonism of M1 receptors in vestibular apparatus

32
Q

What is the species difference in the importance of dopamine receptors in emesis?

A

D2 receptors in CRTZ mor important in DOG

33
Q

How is the species difference in the difference in the importance of D2 receptors clinically relevant?

A

APOMORPHINE - a D2 agonist, is a potent EMETIC agent in the DOG but not the cat

34
Q

What receptors may be more important in cat emesis?

How is this clinically relevant

A

Alpha 2 adrenergic receptors

Xylazine more potent emetic in cats

Prochloperazine (a2 blocker) might be more useful that’s metaclopramide (dopamine antagonist)

35
Q

What is the species difference in cytotoxic drug induced emesis?

A

In cats - mediated by serotonin receptors in CRTZ

In dogs - visceral and vagal afferent serotonin receptors

36
Q

What are some anti-ulcer drugs ?

A 
Nonsystemic antacids 
H2 receptor antagonists 
Sucralfate 
Misoprostol 
Omeprazol
37
Q

How does omeprazole act as an anti-ulcer drug?

A

Blocks proton pump for HCl production

Licensed for horses, not cats or dogs (but increasingly being used off licence)

38
Q

How does sucralfate act as an anti-ulcer drug?

When is it indicated?

A

Sticks to lesion like a plaster

Symptomatic treatment of gastric ulcers - can be useful for chronic ulcers

39
Q

When are anti-ulcer drugs indicated?

A

Treatment of confirmed gastric ulceration

Management of diseases where gastric ulceration is a risk

To prevent secondary oesophagitis in severe vomiting

40
Q

Are anti-ulcer drugs indicated for every case of vomiting?

A

No

Gastritis does not mean gastric ulceration

(Ulceration goes through to the mucosa)

41
Q

Discuss the pros and cons of non-systemic antacids.

A

Inexpensive

Oral administration - problem for vomiting patients

Frequent administration required - poor owner compliance

Doesn’t treat problem, only symptoms

42
Q

Describe the action of Cimetidine, ranitidine and famotidine

A

H2 receptor antagonists - prevents gastric acid production

Effective in TREATING gastric ulcers

43
Q

When are H2 receptor antagonists indicated?

A

NSAIDs, uraemia

44
Q

Discuss the pros and cons of Cimetidine (Zitac)?

A

Only veterinary licensed product

Has the highest frequency of dosing therefore limitied client compliance

45
Q

What would be the best H2 receptor antagonist to use?

A

Ranitidine (Zantac)

Also has prokinetic activity (especially in upper GI tract)

Less frequent dosing required for efficacy - enough justification to use off label

46
Q

When might electrolyte solutions be indicated?

A

Large animal - calves with diarrhoea

Small animal - not so much - gives owner something to do

47
Q

When might motility enhancing drugs be indicated?

A

Rabbits - ileus

Cats - megacolon

48
Q

What are the key motility enhancing drugs (in order of efficacy)?

A

Cisapride

Ranitidine

Metaclopramide

49
Q

Why might ranitidine be used over cisapride?

A

Reduced availability of cisapride

50
Q

What is the effect of opioids on gut transit?

A

PROLONG intestinal transit time

Increase segmental contractions in gut, fluid stays in for longer to be absorbed

HARDLY USED

51
Q

When might opioids be indicated?

A

RARELY

More important to treat underlying cause

52
Q

When might anticholinergics be indicated?

A

Used in management of spasmodic colic in horses

53
Q

Why are drugs which reduce gut motility rarely indicated?

A

Most patients have hypomotile rather than hypermotile gut

Reduction in peristalsis can result in delayed gastric emptying and ileus

May be justified for short term relief from pain associated with large bowel inflammatory disease

54
Q

When might probiotics be indicated?

A

Little confirmed efficacy BUT

Do no harm and give owners something to do

STOPS PRESSURE TO PRESCRIBE ANTIBIOTICS for acute self resolving diarrhoea

55
Q

When MIGHT antibiotics be indicated for GI disease?

A

IBD - metronidazole

Symptomatic treatment of colitis - sulphasalazine

Histiocytic colitis (in boxers and related breeds) - fluoroquinolones

Vomiting - ONLY if infectious cause suspected

BVetMed3 POS - Pharmacology (2 decks)

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