GIT drugs Flashcards
When might it be inappropriate to use anti-emetic therapy? 3
- GIT infections (may prolong infections, especially bacterial)
- GIT obstruction (may increase gastric motility leading to perforations)
- GIT toxicity (may prevent elimination of toxin)
What structures feed into the vomitting centre? (6)
- Higher CNS (pain, fear smell)
- vestibular (motion sickness, inner ear infection)
- Nucleus tractus solitarius (integration)
- Peripheral receptors (GIT, abdominal organs)
- toxins
- CRTZ
How do cats and dogs differ in terms of anti-emetics?
The receptors they have differ in terms of importance of receptors in emesis.
- D2-R in dog CRTZ most important (targetted with apomorphine)
- alpha2-adrenergic receptors more important in felin CRTZ (xylazine more potent in dog v cat, prochlorperazine more useful than metclopramide (DA antagonist) in cats)
- Histamine is a potent emetic in the dog, not cat
Name the 6 classes of anti-emetic drugs
- NK1 antagonists
- Metclopramide
- Phenothiazines
- Antihistamines
- 5HT3 antagonists
- Anti-cholinergics
What is maropitant?
General name of a NK1 antagonist (a class of anti-emetic)
Where/how does maropitant act?
Selective antagonist of substance P at NK1 receptor at the nucleus tractus solitarius (where final common pathway leading to vomiting centre are integrated therefore very potent). Effective against peripheral and central stimuli
Uses of maropitant (3)
Canine anit-emetic (acute gastroenteritis, cytotoxic-induced vomitting, motion sickness).
Considerations when using maropitan (4)
- v effective so take care
- use symptomatically only
- invetigate thoroughly before re-prescribing
- don’t use if suspicious of GI obstruction
How does metoclopramide work?
- Antagonist (D2 dopaminergic and 5HT3 serotonergic. Acts on both of these in the CRTZ and the peripheral receptors)
- Peripheral pro-cholinergic effect (i.e. increases GIT motility)
Inidcations - metoclopramide
- Various emesis-inducing disorders (central or peripheral)
- cancer chemotherapy
- gastroesophageal refluc
- decreased gastric emptying (associated with inflammatory GIT disorders, gastric ulcers, gastric neoplasia, autonomic neuropathy - DM, pyloric stenosis, postop gastric volvulus, hypokalaemia, abnormal gastric motility)
How do phenothiazines work? (6) Where?
Antagonise:
- a1 and a2 (vomiting centre) adrenergic receptors
- D2 dopaminergic receptors (vestibular and CRTZ and peripheral receptors)
- H1 and H2 histaminergic receptors (CRTZ)
- muscarinic hcolinergic (vestibular)
Indications - phenothiazines
Any central or peripheral cause
Not UK veterinary registered therefore few UK indications for use
Name 2 antihistamines (general names)
Diphenhydrinate and diphenhydramine
Where do anti-histamines work as anti-emetics?
H1 and H2 receptors in CRTZ (for canine motion sickness - CRTZ connected with the vestibular system , cats suffer less from this).
Off label use in UK
Examples of 5HT3 antagonists
Dolasetron (Anzemet -trade name)
Ondansatron (Zofran - trade name)
Cisplatin - used to control cytotoxic drug-induced emesis
2 considerations of 5HT3 antagonists
Better than metoclopramide (efficacy-wise)
Expensive
Where do 5HT3 antagonists act? (2)
CRTZ and peripheral receptors
Name 4 anti-cholinergics
atropine, butylscopolamine, propantheline and isoproamide
Advantage/disadvantage of anti-cholinergic anti-emetics:
+ effective for motion sickness due to antagonism of M1 receptors in vestibular apparaus
- also acts on M2 receptors resulting in potential for delayed gastric emptying and ileus.
Where do anti-cholinergic anti-emetics work?
M1 - vestibular and CRTZ
M2 - peripheral receptors
5 classes of anti-ulcer drugs:
- nonsystemic antacids
- H2 receptor antagonists
- sucralfate
- misoprostol
- omeprazole
Why use/not use non-systemic antacids? (4)
Cheap
Oral (problematic if vomiting)
Frequent administration (at least every 4 hour)
Treats but doesn’t prevent
Name 2 H2-receptor antagonists
Cimetidine (veterinary licensed)
Ranitidine and famotidine (not veterinary licensed)
Uses of H2-receptor antagonists
- treating gastric ulceration (from variety of disorders - NSAIDs and uraemia)
- Equally effective at promoting ulcer healing (different potencies affect dosage not efficacy)
- Consider that is it is cheap, convenience for owner? concurrent drug therapy?
