Treatment of Vomiting and Gut Motility Disorders Flashcards
What is the central neural regulation of vomitting controlled by?
2 seperate units both in the medulla
1) the vomitting (emetic) centre
2) The chemoreceptor Trigger Zone, CTZ (passes messages on to the vomitting centre)
Where are the vomiting centre and CTZ located?
- CTZ is located posterior to vomitting centre in area postrena and area of the 4th ventricle
- Both in medulla
What is the vomiting centre?
- Collection of multiple sensory, motor and control nuclei
- Mainly in the medullary and pontile reticular formation, also extending into spinal cord
- Receive nerve impulses from both vagal and sympathetic afferent nerve fibres
- Responds to the incoming signals to coordinate emesis
What is the Chemoreceptor Trigger Zone?
- Sensitive to chemical stimuli and is the main site of action of drugs which stimulate vomiting
- The CTZ is also concerned with the mediation of motion sickness
WHat is the primary origin of motion sickness stimuli?
Vestibular apparatus
What area do medications have the greatest affect on vomitting?
Chemoreceptor Trigger Zone
Describe the pathway for motion sickness
Vestibular labyrinth -> Vestibular nuclei (brain stem) -> cerebellum -> CTZ -> Vomiting centre -> Vomit
What can labyrinthitis cause?
Vomitting
What can trigger nausea/vomiting?
- Stimulation of the sensory nerve endings in the stomach and duodenum
- Stimulation of the vagal sensory endings in the pharynx
- Drugs or endogenous emetic substances
- Disturbances of the vestibular apparatus
- Various stimuli of the sensory nerves of the heart and viscera
- A rise in intracranial pressure
- Nauseating smells, repulsive sights, emotional factors
- Endocrine factors
- Migraine
What is nausea?`
- Feeling of wanting to vomit
- Associated with autonomic effecrs: salivation / pallor / sweating
- Often pro-drome of vomiting
What is retching?
- Strong involrntary effort to vomit
- Unproductive
What is vomiting?
Expulsion of gastric contents through the mouth
What can projectile vomiting be due to?
Suggestive of gastric outlet or upper GI obstruction
What can haematemesis be due to?
Vomiting fresh or altered blood (coffee-grounds) e.g oesophageal varices, bleeding gastric ulcer
What can early-morning vomiting be due to?
- Pregnancy
- Alcohol dependance
- Some metabolic disorders (uraemia)
What are the potential indications for anti-emetic drugs?
- Severe vomiting during pregnancy / hyperemesis gravidarum (when dehydration becomes a severe factor)
- Postoperative nausea and vomitting
- Motion sickness
- Other vestibular disorders
- N/V induced by cytotoxic chemotherapy
- Paliative care
- N/V associated with migraine
What are some types of anti-emetic?
- Antihistamines (H1)
- Antimuscarinics (M1)
- Dopamine antagonists (D2)
- 5HT3 antagonists
- Neurokinin1 receptor antagonists
- Synthetic canabinoids (CB1)
- Steroids
- Other neuroleptics
What receptor antagonists are antihistamines?
H1 histamine receptor antagonists
What are antihistamines useful for treating?
Motion sickness + vestibular disorders
What can be the side-effects of of antihistamines?
Drowsiness and anti-muscarinic effects
What are some examples of antihistamines?
- Cinnarizine; motion sickness, vestibular disorders
- Cyclizine; motion sickness
- Promethazine; severe morning sickness
What is an example of an antimuscarinic useful for treating motion sickness?
Hyoscine Hydrobromide
What are the side effects of anti-muscarinics?
- Constipation
- Transient bradycardia
- Dry mouth
What do antimuscarinics block?
Muscarinic receptor-mediated impulses from the labyrinth and from visceral afferents
What form are antimuscarinics given in?
Patches as well as tablets
What do Dopamine (D2 receptor antagonists work against?
- CTZ-triggered vomiting but not stomach-induced vomiting
- Act centrally as dopamine antagonists on the CTZ
What are some examples of Dopamine (D2) receptor antagonists?
- The phenothiazines and related drugs These are also classed as neuroleptics/antipsychotics Chlorpromazine Prochlorperazine - Domperidone - Metoclopramide (prescribed a lot)
What can be the side-effects of Dopamine (D2) receptor antagonists?
- Can be quite severe
- Can have anti-psychotic medication side-effects e.g movement disorders, tick disorders
- Can last after medication stopped
What are 5HT3 antagonists often used for?
Palliative care and chemotherapy (cytotoxics)
What receptors do 5HT3 antagonists block?
5HT3 receptors in GI tract and in the CNS
Give an example of a 5HT3 antagonist
Ondansetron
When would a Neurokinin receptor antagonist be used?
Adjunct to dexamethasone and a 5HT3 antagonist in preventing N/V associated with chemotherapy
- Sustained vomitting unresponsive to standard measures
What is an example of a Neurokinin receptor antagonist?
Aprepitant
What receptors do synthetic cannabinoids act on?
CB1 receptors
When are synthetic cannabinoids used?
For N/V caused by chemo unresponsive to conventional anti-emetics
What are common side-effects of synthetic cannabinoids?
Drowsiness/dizziness
When are steroids (e.g dexamethasone) used to treat vomitting?
- Can be used alone to treat vomiting associated with cancer chemotherapy, or in conjunction with other antemetics
- Often used to shrink tumours not just anti-emetic effect also produce appeitie stimulation
What can happen to the colon as a result of constipation?
Colon distention
Why is a PR examination extremely important when a patient presents with diahrohea?
Could really be constipation and hardened stool blocking the anal canal allowing only for liquid stool to pass through
What chart allows us able to be able to analyse the consistancy of stool?
Bristol stool chart (type 1 - 7)
What should you do before prescribing laxatives?
- Ensure the problem is actually constipation
- Check the patient’s “norm”
- Try to reverse the cause; including diet/lifestyle changes (e.g prunes/ornages/liquids in children)
What are the types of laxatives?
- Bulk-forming laxatives
- Stimulant laxatives
- Faecal softeners
- Osmotic laxatives
- Peripheral opoid-receptor antagonists
Give an example of a bulk -forming laxative?
Ispaghula husk
Give an example of a stimulant laxative
Senna
Give an example of a faecal softner
Docusate
Give an example of an osmotic laxative
Lactulose
Give an example of a peripheral opoid receptor antagonist
Methylnatrexone bromide
What are the approaches for treatment of ACUTE diarrhoea?
- Maintanence of fluid and electrolyte balance e.g oral rehydration therapy
- Antimotility drugs
- Antispasmodics (reduce SM tone) e.g hyoscine butylbromide (buscopan), mebeverine
- Occasionally antibacterial agent is indicated e.g. systemic bacterial infection
Give an example of an antimotility agent used to treat chronic diarrhoea
Loperamide (imodium)
Give an example of an adsorbent used to treat chronic diarrhoea?
Kaolin, light
Give an example of a bulk forming drug (useful in controlling diarrhoea assoc. with diverticular disease) used to treat chronic diarrhoea?
Ispaghula
What are the types of drugs used to treat chronic diarrhoea?
- Antimotility agents (loperamide/imodium)
- Adsorbents (NB not for acute) kaolin, light
- Bulk forming drugs (useful in controlling diarrhoea assoc. with diverticular disease); ispaghula
What can be used to treat both diarrhoea and constipation?
Bulk-forming ispaghula
What is contained in bile?
- Bile salts
- Bilirubin
- Cholesterol
- Lecithin
- Plasma elctrolytes
What hormone stimulates gallbladder emptying?
Cholecystokinin (CCK)
What percentage of Gallstones in the UK are cholesterol stones?
80%
How are gallstones usually treated?
Laparoscopic cholecystectomy
What is used to dissolve gallstones?
Ursodeoxycholic acid (mainly if mild symptoms and not amenable to other treatment)
What is prescribed to treat the pain associated with biliary colic?
- Opoids (such as morphine or pethidine), given parenterally and/or diclofenac (NSAID) by suppository
Why is the parenteral/rectal route chosen over the oral route when treating bilary colic and acute cholecystitis?
Overcomes difficulties in absorption caused by vomiting
What is colesytamine?
- Anion-exchange resin
- Reducing gallstones can bind with bile-acids encourages liver to reduce cholesterol
- Relieves pruritus associated with partial biliary obstruction and primary biliary cirrhosis
- Can also be used in some instances of diarrhoea e.g Crohn’s disease related
- Also can be used in hypercholesterolaemia
