GIT Drugs Flashcards
What should antiemetic therapy only be considered as?
Symptomatic therapy
With vomiting what should be done while providing antiemetic therapy?
Determine and resolve underlying disease process
Antiemetic therapy only managing clinical signs
In what three things are antiemetic therapies inappropriate to use?
GI infections
- May prolong infection
GI obstruction
- Could increase motility resulting in perforation
GI toxicity
- May prevent patient from eliminating toxin
When would antiemetics be considered with GI toxicity?
If animal has eliminated toxin already and vomiting is a secondary response
Where is vomiting coordinated?
Vomiting centre in medulla
Various nuclei
What areas feed back to the vomiting centre?
Chemoreceptor trigger zone
- No blood-brain barrier
Peripheral receptors
- Highest in duodenum but go down to large intestine
Toxins
Vestibular
- Motion
- Inner ear infection
Higher CNS
What differs between the different systems that feedback to the vomiting centre?
Neurotransmitter - need to know for different antiemetics
On what does the most common antiemetic in small animals act?
Nucleus tractus solitarius
What are the more important neurotransmitters in dogs?
D2 receptors in chemoreceptor trigger zone
What is apomorphine a more potent emetic agent in and on what does it act?
More potent in dogs
Doesn’t work in cats
D2-dopamine receptor agonist
Which neurotransmitters are more important in the cat and what are two drugs that are potent?
Alpha2-adrenergic receptors in CRTZ
Xylazine and prochlorperazine
Is histamine a more potent emetic in the dog or cat?
Dog
What are the 6 classes of antiemetic drugs?
NK1 antagonists
Metoclopramide
Phenothiazines
Antihistamines
5HT3 antagonists
Anticholinergics
What does Maropitant work on?
Nucleus tractus solitarius
What is Maropitant an effective antiemetic for in dogs?
Acute gastroenteritis
Cytotoxic-induced vomiting
Motion sickness - needs higher dose
Describe how Maropitant acts
Selective antagonist of Substance P at the NK1 receptor
Inhibits final common pathway involved in activating the vomiting reflex in CNS
Doesn’t matter about the source of vomiting stimulus
Effective against both peripheral and central stimuli
If vomiting persists with Maropitant use what needs to be determined?
The cause of vomiting
Drug only treating symptom not cause
What are the three places Metoclopramide acts?
D2 dopaminergic receptors
5HT3-serotonergic receptors
Peripheral pro-cholinergic effect
What is Metoclopramide indicated for?
Various emesis-inducing disorders involving central or peripheral activation of vomiting
Cancer chemotherapy
Gastroesophageal reflux
Decreased gastric emptying
How does metoclopramide prevent gastroesophageal reflux?
Flushing system empties stomach
Gastroesophageal reflux just doesn’t occur
What is decreased gastric emptying associated with?
Inflammatory gastrointestinal disorders
Gastric ulcers
Gastric neoplasia
Autonomic neuropathy (diabetes mellitus)
Pyloric stenosis
Postoperative gastric volvulus patient
Hypokalaemia
Abnormal gastric motility
Which drugs are not registered for animal use in the UK?
Phenothiazines
Which receptors do phenothiazines antagonise?
Alpha 1 and 2 adrenergic receptors4
D2 dopaminergic receptors
H1 and 2 histaminergic receptors
Muscarinic cholinergic receptors
What are the indications for phenothiazines?
Any central or peripheral cause of vomiting
What do antihistamines act upon and what would they be used for?
H1 and H2 receptors in the chemoreceptor trigger zone
Used for motion sickness in the dog not the cat
What are 5HT3 antagonists used to control?
Cytotoxic drug induced emesis
What are some examples of 5HT3 antagonists?
Dolasetron (Anzemet)
Ondansatron (Zofran)
What are anticholinergics effective for?
Motion sickness
Antagonism of M1 receptors in vestibular apparatus
What is the major problem associated with anticholinergics?
Effect on M2 receptors
Result in potential for delayed gastric emptying and ileus (disruption of normal emptying)
What are 5 anti-ulcer drugs?
Nonsystemic antacids
H2 receptor antagonists
Sucralfate
Misoprostol
Omeprazole
Describe non-systemic antacid use
Inexpensive drugs
Frequent oral administration - every 4 hours
Treats but doesn’t prevent
What are the three H2 receptor antagonists?
Cimetidine
Ranitidine
Famotidine
What are H2-receptor antagonists effective in treating?
Gastric ulceration caused by a variety of disorders
- NSAIDs
- Uraemia
What should we base our choice of H2 receptor antagonists on?
Cost
Client convenience
Concurrent drug therapy
What is sulcralfate indicated for?
Symptomatic treatment of gastric ulceration
What is Misoprostol?
Synthetic PGE1
What is the main indication for Misoprostol?
Management or prevention of NSAID toxicity
What does Misoprostol cause and why is it a safety issue?
Causes abortion
Issue in relation to who should handle the drug
What is Omeprazole?
Proton pump inhibitor
Describe the use of Omeprazole in small animal veterinary medicine
Use is increasingly common but off label
Ulcers or oesophagitis refractory to ther anti-ulcers
Ulcers associated with gastrinomas or mast cell tumours
What is Gastroguard (omeprazole) used for?
Equine medicine for treatment and prevention of gastric ulcers
What do electrolyte solutions enhance?
Fluid absorption from the gut
What do electrolyte solutions depend on and are linked to?
Depend on active absorption of glucose and aminoacetic acid in small intestine
Directly linked with water and sodium movement
What are the two types of motility modifying drugs?
Opioids
Anticholinergics
What do opioids do?
Increase segmental contractions in gut (random/multi-directional)
Prolong intestinal transit time
Theoretically allow greater time for fluid to be absorbed
What do anticholinergics do within the gut?
Decrease peristalsis
What can opioids be effective for?
Symptomatic treatment
- Relieve abdominal pain and tenesmus
- Reduce defecation frequency
What are anticholinergics used little in?
Management of diarrhoea in dogs and cats
What are anticholinergics used in?
Management of spasmodic colic in horses
Which GIT drugs need to be avoided in cats?
Adsorbents
Protectants
What are the dose rates of maropitant in dogs for prevention/treatment of emesis due to central/peripheral stimuli?
2mg/kg PO daily for up to 5 days
1mg/kg SC daily for up to 5 days
What is the dose rate for maropitant in the prevention of motion sickness?
8mg/kg PO daily for maximum of two days
How does metoclopramide cause increased gastric emptying?
Promotes release and increased sensitivity to acetylcholine in smooth muscle
Results in:
- Increased tone of lower oesophageal sphincter
- Increased strength of oesophageal contractions
- Increased gastric antral contractions
- Relaxation of pylorus
- Increased smooth muscle contraction in duodenum
What are the side effects of metoclopramide?
Infrequently cause mental changes
- Hyperactivity
- Aggression
- Depression
May cause gastric spasm and enhance vomiting
What are the side effects associated with antihistamines?
Drowsiness
Xerostomia (dry mouth)
What are the side effects of phenothiazines?
Hypotension due to alpha-adrenergic receptor blocking action
What shouldn’t anticholinergic drugs be used in?
Dogs with parvovirus
What could long term use of H2 antagonists cause?
Hypoacidity and bacterial overgrowth in the stomach
Not a clinical concern
What should be done with H2 antagonists in patients with impaired renal function?
Dose should be reduced by 50%
What do calcium, magnesium and aluminium containing antacids tend to promote?
Calcium
- Constipation
Magnesium
- Looser faeces
Aluminium
- Reduced gastric motility
- Delay of gastric emtpying
What may administration of excessive calcium-containing antacids predispose the patient to?
Renal caliculi
What are the treatments for vomiting in both chronic and acute cases?
Chronic
- Find underlying causes
Acute
- Fasting
- Symptomatic treatment
What are the three things that drugs used to treat vomiting tend to affect?
Proton-pump inhibitors
Anti-histamines
Anti-cholinergics
Describe Sucralfate and what it is used in the treatment of
Aluminium hydroxide and sucrose octasulfate
Dissociates in acid
Causes binding to exudate at ulcer sites
Forms a protective barrier and stimulates HCO3, mucus and prostaglandin secretion
Used in treatment of oesophageal and gastric ulceration
What are the dose rates of Sucralfate in dogs?
<20kg: 0.5mg/dog
>20kg: 1mg/dog
What are three HA receptor antagonists used to treat vomiting?
Cimetidine
Ranitidine
Famotidine
Describe the actions of cimetidine/ranitidine/famotidine
Inhibits gastric acid
Some gastric prokinetic activity
Used frequently to treat any sort of regurgitation/vomiting
What is a proton pump inhibitor used for treatment of vomiting?
Omeprazole
Describe the action and use of omeprazole
Proton pump inhibitor
Binds parietal cells blocking H+/K+
Inhibits transport of H+ into the stomach
Used for:
- Gastric hyperacidity
- GI ulcers
- Erosions
- Gastrinomas
What is another name for a gastrinoma?
Zollinger-Ellison syndrome
When should anti-emetic therapy be used?
Debilitating vomiting
Animal in pain
Marked fluid/electrolyte loss
What is the most appropriate anti-emetic treatment?
Management of the underlying disease
Though the cause cannot always be determined in all patients
Why might anti-emetic therapy not always be desirable?
Vomiting can be protective so may not want to get rid of it
Describe the action and use of metoclopramide
Para-aminobenzoic acid derivative
Central and GI effect
Antagonises D2-dopaminergic & 5-HT3 receptors
Upper GI prokinetic agent
Can come in tablets, suspension or injection
What is a 5-HT3-serotonergic antagonist used for treating vomiting?
Ondansetron
What is the best anti-emetic for chemotherapy induced nausea and vomiting?
Ondansetron
What is Ondansetron good for?
Chemotherapy-induced nausea and vomiting
Pancreatitis
What is a neurokinin-1 receptor antagonist?
Maropitant
Describe the action and use of Maropitant
Neurokinin-1 receptor antagonist
Central and peripheral effects
Stops substance P binding
Very potent!
Useful in any kind of vomiting
What is Maropitant licensed for use in and what are the dose rates?
Licensed in dogs - soon in cats
Dose is 1mg/kg sub-cutaneous every 24hrs
2mg/kg orally every 24 hours
What are some surgical emergencies with small animal abdominal pains?
Septic peritonitis
Risk of septic peritonitis
Gastric dilatation and volvulus
Metabolic emergency
Vascular emergency
Pyometra
Dystocia
What are the pros and cons of pure opioids ans analgesia?
Pros:
- Very good
- Reversible
- Sedation
- Constant rate infusion
Cons:
- Sedation
- Decrease GIT motility
- Nausea
- Injectable
What are the pros and cons of using partial agonist opioids for analgesia in small animals?
Pro:
- Good analgesia
- Minimal sedation
- Less effect on GIT motility
- Good transmucosal absorption in cats
Cons:
- Some sedation
- Can decrease GIT motility
What are the pros and cons of using NSAIDs for analgesia in small animals?
Pros:
- Anti-inflammatory
- No sedation
Cons:
- Renal toxicity
- GIT toxicity
