Drugs and the Gastro-intestinal tract Flashcards
what are the characteristics of nausea?
Pallor
Cold but perspiring
Loss of interest in surroundings (and food!)
Salivation
Loss of gastric tone
Reflux of gastric contents into stomach (reverse peristalsis)
What is vomitting?
Vomiting , or emesis is the forcible expulsion of the contents of the upper GI tract (stomach and duodenum) through the mouth.
What is the vomitting centre?
An important source of stimulation is from chemotaxic trigger zone (CTZ) in area postrema
Not protected by BBB
CTZ has many dopamine receptors (so anti-Parkinson’s drugs can → nausea & vomiting)
Dopamine receptor antagonists are antiemetics and are used to suppress CTZ
What are the causes of vomiting?
Extreme stretching of mucous membranes of intestines, particularly stomach
Gut irritants e.g alcohol, spicy foods, bacterial toxins, drugs
Systemic drugs (via chemotaxic trigger zone, CTZ)
Unpredictable movement
Disgust and revulsion
hyper-emesis gravidarum
Can you name some class of Anti emetics?
5HT receptor antagonists e.g ondansetron
Substance P antagonists e.g Aprepitant
Dopamine antagonists e.g Domperidone, haloperidol, metaclopramide
Anti histamine Promethazine, cyclizine
Anti-muscarinic Hyocine
Cannabinoid Nabilone
Which are 5ht antagonists?
Effective at CTZ, so useful in cancer with fewer side effects than dopamine antagonists
Most effective against nausea caused by anti-cancer therapy (drugs and radiation)
5HT also released by enterochromaffin cells of gut (following XRT or drugs) stimulating receptors which also blocked by antagonists
Substance P antagonist?
Found injected substance P → vomiting so investigated → Aprepitant (a NK-1 receptor antagonist).
What are Dopamine antagonists?
D2 receptor antagonists
Work within CTZ
Effective in uraemia and GI disorders
Phenothiazines may be used in pregnancy
Also has a peripheral effect to increase gastric and oesophageal motility (so helpful in reflux)
Metoclopramide is more able to pass the blood\brain barrier, so can be more powerful, but also has more unwanted effects such as movement disorders and fatigue
what antihistimine/muscarinic?
H1 receptor antagonists, directly blocking vomiting centre
Most used of all anti-emetics
Is most effective against motion sickness, can be taken as a patch
is not effective against emesis triggered by CTZ
promethazine been used in pregnancy and by NASA astronauts
What are cannabinoid antagonists?
Nabilone a synthetic cannabinoid
Difficult (initially illegal) to study
Was developed following the accumulation of anecdotal evidence
Well absorbed orally
Effective against stimulants that trigger CTZ
Side effects include dizziness and dry mouth
Also some hallucinatory effects
Who is affected most by constipation?
Is the most common GI complaint
Most common in women (particularly in pregnancy), children and older adults
Occasional constipation is almost universal
30% of the population is frequently troubled by it
Prevalence may be higher – self-treating.
What is constipation?
Difficulty in passing stools or incomplete or infrequent passage of hard stools.
Causes of constipation in Children?
Poorly understood.
Contributing factors
include pain, fever, dehydration, dietary and fluid intake, toilet training problems, the effects of medicines, psychological issues, and a family history of constipation.
Impaired mobility creates a tendency to constipation, particularly in children with physical disabilities such as cerebral palsy. Constipation is also more common in children with Down’s syndrome or autism.
What are alarm signs with constipation?
Constipation alternating with diarrhoea
Blood and / or slime present in stool
Constipation accompanied by abdominal pain or vomiting
examples of laxatives by class?
Classified by action
Stimulants – Senna, Bisacodyl
Bulk forming agents – Bran, isphagula husk
Osmotic laxatives – Lactulose
Stool Softeners – Glycerin suppositories
What are stimulant laxatives?
Irritant or contact laxatives – stimulates the mucosa of the gut.
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