N+V+D Pharmacology Flashcards
What categories are antidiarrheals divided into?
1) adsorbents (not absorbents)
2) antimotility drugs (anticholinergics and opiates)
3) intestinal flora modifiers (aka probiotics and bacterial replacement drugs)
Adsorbents
How do they work?
How is this different from absorption?
When are they used?
- Coat the walls of the Gi tract and binding the causative bacteria or toxin to their adsorbent surface for elimination from the body through the stool.
- Differs from absorption in that it involves the chemical binding of substances onto the surface of an adsorbent while absorbents involve uptake of substance across a surface
- Used in milder cases
Effect of anticholinergics?
When are they used?
- Slow peristalsis by dec the rhythmic contractions and smooth muscle tone of the GI tract
- Often used in combo w opiates and adsorbents
- Used in more severe cases of diarrhea
How do intestinal flora modifiers work?
Who are these especially useful for?
• Products obtained from bacterial cultures mostly lactobacillus (which make up the majority of the bodys normal bacterial flora and are most commonly killed by Abx.
The intestinal flora modifier will replenish the bacteria and suppress disease causing bacteria
•Helpful for pt w antibiotic induced diarrhea
Do intestinal flora modifiers typically have many adverse effects?
Antidiarrheals in general?
No
•varies but most are minor and not life threatening
How are opiates used as antidiarrheals?
- Dec bowel motility (allowing more absorption and dec stool freq and volume)
- dec pain caused by rectal spasms
- used in more severe cases of diarrhea
diphenoxylate hydrochloride with atropine sulphate
What class?
How does it work?
Opioid
• acts on sm muscle of GI tract to dec GI motility and excess GI propulsion
• little to no analgesic effect
Why is atropine added to diphenoxylate?
added to discourage recreational use (it has cholinergic effects eg dry mouth, abdm pain, tachy when taken in lg doses)
Why do you need to use pepto-bismol w caution with children?
D/t reyes syndrome
Should antidiarrheals be used at home with children?
Always contact doctor first!
What does CTZ stand for in pathway of N+V in brain?
VC?
CHemoceptor Trigger Zones
Vomiting center
How does pathway work in initiation of N+V in brain?
- The VC is area of brain responsible for initiation of the physiological events that lead to N and eventually V
- Neurotransmitter signals are sent to VC from the CTZ (another area of brain involved in induction of N &V
- The signals alert these areas of brain to the nauseating substances that need to be expelled from body
- Once CTZ and VC are stimulated theyll initiate the events that trigger V reflex
What neurotransmitters are involved in N+V?
Ach, dopamine, histamine, prostalgandins, serotonin
What drug that we’re required to know is an example of an Anticholinergic
scopolamine
prochlorperazine
How do anticholinergic drugs work in r/t vomiting?
- Block ACH receptors on vestibular nuclei. When bound this blocks nausea inducing signals and prevents them being transmitted to CTZ. Also blocks signals from getting to vomit centre
- Also tend to dry GI secretions
Scopolamine is commonly used for?
motion sickness, adjunct to anesthesia to inhibit salivation and excess resp secretion, causes amnesia and sedation. Often comes in patch
Neuroleptic drug example?
prochlorperazine
Action of neuroleptics?
- Were used for antipsychotic effect but also prevent N&V by blocking dopamine receptors on CTZ
- Often have anticholinergic effects
How is prochlorperazine used besides as an antiemetic?
to treat psychotic disorders
Example of prokinetic drugs?
metoclopramide
How do prokinetic drugs work?
primary action is to stim peristalsis in the GI tract which enhances the emptying of stomach contents into duodenum
• Also block dopamine receptors in CTZ
Metoclopramide hydrochloride used for?
used as antiemetic and to treat delayed gastric emptying and gastroesophageal reflux
Example of serotonin blockers
ondansetron
Action of serotonin blockers?
- Blocks serotonin receptors in Gi tract, CTZ and VC
* There are many subtypes of receptors
Most antiemetic and antinausea drugs cause what as side effect?
Drowsiness
Goal of antiemetic tx is?
to prevent fluid& electrolyte disturbances, dec deterioration of pt nutritional status and blunt the memory of the nausea and vomiting experience
3 main mechanisms by which nausea and vomiting is triggered in brain?
1) Chemoreceptor trigger zone (CTZ) → relayes message to VC
2) Visceral Nerves (vagus + GI nerves) → send messages to CTZ if you overeat, etc…
3) Higher CNS/vestibular (cerebral cortex, sensory organs, vestibular apparatus (ear)) → relays directly to VC
- All routes go through VC
What neurotransmitters are released by each of the pathways by which nausea + vomiting?
(Or are these the neutransmitters that ACT ON that area??…slides unclear)
Visceral: dopamine + serotonin
CTZ: dopamine + serotonin
Higher CNS: Histamine and Acetylcholine, Serotonin
What kind of stimulants cause N+V through each of the 3 pathways?
Visceral: overeating, pain, MI
CTZ: drugs, hormones, toxins, metabolic abnormalities
eg. Action of opioids, chemotherapy, pregnancy
Higher CNS/vestibular: Triggered by emotions, smells, anticipatory nausea, motion sickness, vertigo, taste, gag reflex
Where is the vomiting center located?
CTZ location? Why is CTZ affected by chemicals?
Both in medulla oblongata
CTZ Outside the blood brain barrier, so exposed to systemic toxins, drugs etc.
CTZ
Is prime site for what kind of triggers?
The prime site of ‘systemic’ triggers of vomiting
Triggered by drugs, hormones, toxins, metabolic abnormalities
eg. Action of opioids, chemotherapy, pregnancy
Name 6 kinds of antiemetics
1) Anticholinergics
2) Antihistamines
3) Neuroleptics
4) Prokinetics
5) serotonin blockers
6) Tetradrocannabinoids
How does visceral stimulation occur?
Triggered by afferent fibres mainly from our GI tract, but also cardiac nerves (direct visceral irritation and/or distension)
eg.Gastroenteritis, overeating, MI
Triggered by mechanical or chemosensory receptors
Stimulated by both sympathetic and parasympathetic fibres (primarily the Vagus Nerve), which connect to the CTZ
By what mechanism is the higher CNS a propagator of N+V? Stimuli here?
Stimulated by nervous inputs from higher neurological centres, including other cranial nerves
CN VIII (vestibular component) in particular can be linked to nausea
The Gag reflex(CN IX afferent fibres) provides a strong trigger
As with pain, there is a psychological/cerebral cortex component of nausea.
–> sensory stimuli
What kinds of meds act well against N+V caused by stimulation of CTZ?
Serotionin Receptor Antagonists (5HT) - ondansetron
Dopamine Receptor Antagonists (DA) - prochlorperazine, metochlopramide
Glucocorticoids
Benzodiazepines
Drugs for if visceral nerves are cause of nausea?
Serotonin Receptor Antagonists (5HT) - ondansetron
Dopamine Receptor Anagonists (DA) - prochlorperazine, metochlopramide
nausea caused by post-op or chemotherapy responds well to?
Using a combination of drugs
as are different stimuli?
If visceral stimulation is cause of nausea, what is important to treat in addition to the nausea itself?
The PAIN
Take care when using metoclopramide for visceral nausea…why?
If SBO is cause of nausea, this med will increase discomfort!
Is contraindicated in small bowel obstruction
Find out why….
When do you want to make treat V+N?
something like food poisoning – need to purge body of this or could become dangerously ill
What drugs in addition to antiemetics may be helpful and why?
Glucocorticoids + benzodiazapines (ativan) might be needed
– benzos for psychological component (anticipatory nausea)
- reason for corticosteroids being so effective is unknown
Why is ondansetron more likely to be effective for nausea?
works on serotonin so acts on more pathways
Tactics for treating nausea d/t sensory organs (part of high CNS pathway)?
- Remove stressor (smell, sight, sound)
- Aromatherapy
- Relaxation
Which drugs act well on the vestibular apparatus?
(as is part of higher CNS)
Antihistamines
Anticholinergics
What are triggers of nausea r/t the cerebral cortex and how can these be remedied?
- Stress, nervousness, emotional imbalances
- Benzos, cannainoids, relaxation
Which drugs are Dopamine receptor antagonists?
Prochlorperazine, Metoclopramide
Which drugs are antihistamines?
Diphenhydramine, Dimenhydrinate
