GI drugs Flashcards

1
Q

Clinical signs of gastrointestinal injury or disease

A

Vomiting diarrhoea
Constipation
Colic
Bloat
All are physiological functions intended to protect the animal from harmful substances that may have been ingested

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2
Q

Gastric means

A

Stomach

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3
Q

Eneteric means

A

small intstine

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4
Q

Colonic means

A

Large intestine

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5
Q

Gastrointestinal movement control by:

A

Nervous system
- Parasympathetic- stimulates receptors with acetylcholine
- Vagus nerve carries nerve impulse to and from abdominal organs
Hormones
Endocrine system

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6
Q

How does the parasympathetic system affect the GI system

A

stimulates receptors wit acetylcholine
Vagus nerve carries nerve impulse to and from abdominal organs
Drugs that mimic acetylcholine
- Increased digestive secretions
- Improve blood flow
- Increased gut smooth muscle tone and mobility

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7
Q

How does the sympathetic system effect the GI system

A

stimulates receptors with norepinephrine; stimulates adrenal gland to release epinephrine
Decreased blood flow to GIT
Decreased gastric and enteric motility
Decreased secretions
Therefore- decreases digestion and absorption of nutrients

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8
Q

Emetic centre of the brain is

A

A group of special neurons located in medullary portion of brain
Sends and receives neurons to stimulate the vomiting reaction
Coordinates smooth muscle contractions and the act of vomiting itself
Horses, rabbits, rats and guinea pigs cannot vomit

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9
Q

Major receptors associated with emetic or antiemetic drugs include

A

Serotonin
Acetylcholine
Histamine
Dopamine
norepinephrine/epinephrine

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10
Q

Stimulation of vomiting via 5 mechanisms

A

Binds to receptors within emetic center and stimulates neurons
Bind to receptors on chemoreceptor trigger zone (CRTZ) which send signal to emetic center
Located adjacent to emetic center within the brain
Local nerve signals from distended or irritated regions such as pharynx, stomach, duodenum etc.
Signals from overactive inner ear balance mechanism
Emotional centres in brain–due to trauma or emotional upset

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11
Q

Chemoreceptor trigger zone (CRTZ) is

A

Monitors blood and CSF for chemicals that can stimulate vomiting
Has all major receptors found in emetic centre and also receptors for opioids
The number and types of receptors varies with species and individuals
Cats have increased population of alpha receptors pn emetic center so epinephrine and norepinephrine stimulation or drugs that stimulate these receipts will increase likelihood of vomiting
Dogs have less alpha receptors
Dogs have more dopamine receptors than cats

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12
Q

Emetics are

A

Drugs to induce vomiting

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13
Q

What are the mechanisms of action for emetics

A

Central acting emetics turn on the chemoreceptor trigger zone and/or vomit center located in the brain. Body senses presence of a “toxin” and triggers vomit to protect self
Peripheral acting emetics irritate/activate nerves in the stomach

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14
Q

Indications of emetics

A

Toxin ingestion
Must be given within 4 hours of ingestion
Removes 40-60% of gastric contents with each vomit
Works best if small amount of food given prior
Many toxins already cause vomit; do not need to give an additional emetic. Ask owner for history

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15
Q

Contraindications of emetics

A

Never induce vomit if caustic, acid or alkaline (can burn esophagus and lungs)
Never induce vomit if FB
Never induce vomit if unconscious or seizing
Never induce vomit in horses, ruminants, birds, rabbits, most rodents who can’t vomit
Never induce vomit of bloat, gastric torsion or esophageal damage
Always check MSDS or poison control before inducing vomit

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16
Q

What toxins should you use emetics for

A

Rodenticides
Most medication overdoses, including NSAIDs, anti-parasitics, coccidiostats
Anti-freeze
Chocolate
Plant toxicities (lily, foxglove,…)
Vomit within 4 hours of ingestion is most effective; otherwise
Some toxins (i.e., chocolate) may cause vomit at a certain dose
ALL toxins have a species-specific toxic dose

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17
Q

What are some centrally acting emetics

A

Mu-acting opioids
Alpha-2 agonists

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18
Q

Mu-acting opioids as an emetic

A

Turns on the chemoreceptor trigger zone and vomit center of the brain
Only works on first dose
Need high enough first dose, otherwise sedation occurs and turns down vomit center
Some animals will not respond
Can reverse with naloxone after vomited

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19
Q

Most commonly Mu-agonist opioid as an emetic is

A

Hydromorphone and apomorphine

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20
Q

Apomorphine as an emetic

A

1st choice in dogs
Conjunctival tablet form
Can dissolve in sterile saline and squirt into conjunctiva (rec flush after as irritating) Or filtered via micro-filter (to sterilize) and then give IV
1st dose only
Not in cats- they lack the receptors in the CRTZ

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21
Q

Hydromorphone as an emetic

A

1st dose only in SA (best in dogs)
IM works best. SQ works. IV does NOT induce vomit because sedation hits too fast – now aspiration risk
More sedation than apomorphine

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22
Q

Alpha-2 agonists as an emetic

A

1st choice in cats
Produces emesis in 90% of cats only 30% in dogs which have less α 2 receptors in CRTZ

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23
Q

Local emetics are

A

Hydrogen peroxide (3%)
Warm salt solution

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24
Q

Hydrogen peroxide (3%) as an emetic

A

Direct irritant
Damages mucosal lining of the stomach
There is a per kg dose AND a maximum dose of 3 tbsp (45 mls) for any sized animal. Can’t exceed maximum dose.
Give one dose, wait 15 mins. Can repeat once.
Will cause serious s/e if gets into lungs (corrosion, hemorrhage, necrosis)
Can cause gastric perforation if give too much; risk still exists if given at recommended dose; increased risk if pre-existing erosion/ulcer and in certain patients

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25
What do you do when using warm salt solution as an emetic
must give water or IV fluids to reduce risk of salt toxicity or dehydration
26
Antiemetics work by
Can block CRTZ Can block vomit center Can control nausea Can dampen peripheral nerves in GI tract
27
When and how to give antiemetics
Give 1st dose parenterally so will be absorbed Give when natural vomiting reflex in excessive and not considered helpful e.g. pancreatitis
28
Phenothiazine tranquilizers (acepromazine) works how as an antiemetic and SE
Works by blocking several types of receptors in CRTZ and vomiting center. Side effects - ↓ BP - Small degree of sedation at antiemetic dose - Often used for motion sickness
29
What are some commonly used antiemetics
Phenothiazine tranquilizers (acepromazine) Prokinetic drugs such as Metoclopramide Serotonin antagonist Maropitant
30
How does Metoclopramide (Reglan®) work as an antiemetic
Blocks several receptors centrally and locally. ↑upper GI motility (stomach and small intestine) ↑muscle tone of lower esophagus Relaxes pyloric outflow ↑ gastric motility in normal direction without increasing secretions All the above improves GIT flow in an aboral direction.
31
When and when not to use prokinetic drugs
Used for intermittent vomiting of bile and mucus in otherwise healthy dogs Don’t use in animals prone to seizures Anticholinergic drugs contraindicated as they reduce gut motility
32
Serotonin antagonist as an antiemetic and when to use it
Newer classes of antiemetic’s e.g. ondansetron Binds to serotonin receptors in CRTZ and inhibits release of serotonin. Used in dogs and cats with refractory vomit that doesn’t respond to other drugs Parvovirus in dogs Pancreatitis in cats
33
How does Maropitant (Cerenia®) work as an antiemetic and when to use it
Action: blocks neurokinin 1 receptors (NK1) in the vomit centre Used to prevent motion sickness and vomiting. Start with injectable (SQ), then switch to oral form
34
How do anti-diarrheals work
Drugs that affect motility - slow down peristalsis so there is increased absorption of water from the feces; feces becomes firmer Blocking secretions Adsorbents and protectants stay in the GI tract Soothe the GI tract; firm up stools Bind to toxins and irritants causing the diarrhea Antibiotics, prebiotics, probiotics treat abnormal GI flora and restore normal flora
35
What are some classes of anti-diarrheals
Motility modifiers Blocking secretions Absorbants and protectants Drugs that affect intestinal flora
36
What drugs work as motility modifiers for diarrhea
Opioids/Opioid-Related Agents Mu-receptor agonists
37
How do Opioids work as motility modifiers for diarreha
Decrease peristalsis, increase segmental contractions; overall effect is absorption of fluid from colon S/e: sedation/excitement, ileus to constipation Ex. Imodium® is a human OTC; Diphenoxylate (Lomotil®) Caution with breeds with MDR1 mutation Use with caution if cause of diarrhea unknown
38
What anti-diarrehals block secretions
Anything that increases the effect of acetylcholine or the activity of the parasympathetic nervous system can also increase GI tract secretions e.g. organophosphates
39
How does blocking secretions work for anti-diarrheals
Irritation/Stimulation of cells lining GI tract result in sections of ions that osmotically pull water into the lumen of the gut e.g. bacterial endotoxins Inflammation of these cells can cause damage to point of blood to escape into lumen resulting in bloody diarrhea. Potential for dehydration especially in young
40
What drugs stop Gi secretions
Salicylates=anti-inflammatory action (Pepto-Bismol) – to be discussed again with protectants Sulfasalazine- contains a Sulfonamide antibiotic component Side effect –keratoconjunctivitis sicca (dry eye)
41
How do absorbents and protectants work for diarrhea
Stay in the GI tract; not absorbed Coats intestinal mucosa Soothes inflamed gut Forms a barrier effect Adsorbents also bind to irritants, toxins Some can promote fibrosis/healing Some will solidify diarrhea (owners like this!) May not address underlying issue
42
Adverse effects absorbents and protectants for diarrhea
Few adverse-effects Take 1-2 hours after other oral drugs or may impair their absorption
43
How does Bismuth subsalicylate (PeptoBismol®) work and when to avoid
OTC/ELDU Contains 2 drugs: - Subsalicylate (aspirin derivative) is anti- inflammatory - Bismuth coats the intestines - protectant Caution or avoid in cats (aspirin-based toxicity) May blacken stool (masks melena)
44
Types of absorbent and protectants for diarreha
Bismuth subsalicylate (PeptoBismol®) - OTC/ELDU Kaolin/pectin (Kaopectate®) - OTC/ELDU Barium Activated Charcoal
45
Barium is used when for diarreha
Protectant and absordent Radiocontrast agent; outlines GIT Lines, soothes, absorbs, firms stool Always alert ASAP if accidentally delivered into airways when giving by stomach tube; may need emergency treatment as causes lung damage
46
Activated charcoal as a protectant for Gi tract
Fine black porous powder, absorbs toxins Stays in GIT; acts as a sink and draws toxins from circulation Effective if given within 4 hours of ingesting toxin If the toxin undergoes entero-hepatic recirculation, can give even if more than 4 hours have elapsed from ingestion Liquid can be syringed or stomach tubed into mouth; mix well before use (settles) Warn owners may have vomit or black diarrhea initially; will stain
47
Why would you use drugs that affect GI flora with diarrhea
Upset of regular GI flora is a cause of diarrhea and often secondary to other causes of GI inflammatio
48
What drugs effect he intestinal flora
Metronidazole Tylosin Prebiotics Probiotics
49
Metronidazole works by and is used when
Most common antibiotic for diarrhea in SA Very effective against anaerobes (Clostridia) and Giardia S/e: v/d, neurological symptoms
50
Tylosin is used in what
Most common in cattle/swine not horses
51
Prebiotics are used when
Given to promote growth and survival of beneficial bacteria in the gut Ex. Vit B12, folate, iron, specific sugars
52
Probiotics are used when
Live, beneficial bacteria. Not a drug. Anaerobic (use ASAP after exposing to air) Ex. Prostora® (Iams), yoghurt with live cultures
53
Laxatives, Cathartics and Purgatives do what
Drugs that increase poo with increasing degrees of aggressiveness Work by increasing fluid content of stool or irritating gut to increase peristalsis increasing BMs Used for: constipation, hairballs, to empty GI tract prior to GI surgery
54
Irritant laxatives are and used when
Chemical irritant; stimulates nerve endings in intestines to increase peristalsis May have systemic s/e Ex. castor oil, bisacodyl Different classes: Laxatives - mild Purgatives - stronger Cathartics - strongest (cramping, straining)
55
Osmotic laxatives work how and side effects
Pull water in the colon (into feces so softer and easier to move) S/e: dehydration, constipation, dependence (cannot stop abruptly); salt- based laxatives may disturb electrolytes
56
Examples of osmotic laxatives
Lactulose- sugar that is not absorbed by the intestines; draws water. Milk of magnesia, Epsom salts
57
Bulk forming laxatives are and work by
Insoluble fibre Incorporates into feces; increases fecal bulk so looks normal and absorbs water Ex. psyllium(Metamucil),bran, pumpkin Used to prevent & treat sand colic in horses
58
Emoilient laxatives are and work by
Detergent–like chemicals reduce stool surface tension so water is absorbed into fecal matter Few side effects Ex. docusate sodium succinate (Note: Osmotics, bulk-forming and emollients all work by increasing water content in poo)
59
Lubricants for the GI tract are and work by
Coats GI tract and feces and helps to slide things along; passes faster with less effort Ex. mineral oil (stomach tube only, do NOTget into lungs), white petroleum or cod liver oil (hairball formulas for cats), glycerine
60
What drugs decrease stomach acid
Antacids Histamine-2 Receptor Antagonists Proton Pump Inhibitors
61
How do antacids work
Buffers and alkalinizing agents In the stomach and chemically neutralize pH of the gastric juice TUMS®, Rolaids®
62
Side effects of antacids
Will alter ionization of other oral drugs work; give 1-2 h apart Chronic use causes gastric acid rebound syndrome- body responds by increasing acid production. Avoid chronic use Alter absorption of tetracyclines
63
Histamine-2 Receptor Antagonists decreases stomach acid by and when
In a normal body, histamine binds to H2- receptors and stimulates HCl production Anti-histamines bind to and block H2-receptors E.g. ranitidine (Zantac®), famotidine (Pepcid)
64
Proton pump inhibitors are used for and how do they work
Decrease stomach acid Most effective, fewest s/e; $$ Drug binds to H+ pumps; blocks H+ ions from getting into the stomach lumen Good for chronic use Often co-prescribed for chronic steroid or NSAID therapy (decreases GI side effects) E.g. omeprazole (Gastrogard®)
65
Mucosal Protectants as an antiulcer med are
Sucralfate (Sulcrate)
66
Mucosal Protectants as an antiulcer med mechanisms
Intestinal Band-Aid; binds to existing ulcers and forms barrier Provides a scaffold for fibrocytes to adhere; hastens healing time of ulcers Stimulates prostaglandin production increases secretion of protective mucus May interfere with absorption of other drugs; give 1-2 hours apart
67
Appetite stimulants are used when
Most frequently used in cats Chronic renal disease, pancreatitis, FURD; ANY cause of stress or illness can cause a cat to stop eating Band-aid; does not address underlying problem
68
What are some common appetite stimulants
Cyproheptadine (Periactin®) Diazepam
69
When to use Cyproheptadine (Periactin®) as a appetite stimulant and side effects
Human anti-depressant; works in cats S/e: aggression and excitement
70
How to use diazepam as an appetite stimulant
Up to 4 doses max in cats; otherwise will increase risk of acute hepatotoxicity Can give IV or PO
71
What are some drugs that can treat bloat
Ruminatorics Antifoaming drugs
72
How do Ruminatorics work
Stimulate rumen motility by activating the PNS (ex. indirect-acting cholinergics) E.g. neostigmine
73
When and how to use antifoaming drugs
Used to treat frothy bloat E.g. dioctyl sodium succinate (DSS) (Antigas®) Decrease surface tension on foam bubbles and cause them to break down. Smaller bubbles can be passed through a stomach tube; gas can be belched Large volume administered by stomach tube directly into rumen Do NOT get into the lungs
74
Ionophores - Rumensin® are and used when
Group of antimicrobial drugs used to control coccidia in poultry and cattle. Used in beef and dairy cattle to balance the rumen population of microorganisms to improve conversion of cattle feed into weight and to prevent bloat. Toxic to horses – do not add to horse feed
75