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Pharmocology > GI drugs > Flashcards

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
Q

What do you do when using warm salt solution as an emetic

A

must give water or IV fluids to reduce risk of salt toxicity or dehydration

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26
Q

Antiemetics work by

A

Can block CRTZ
Can block vomit center
Can control nausea
Can dampen peripheral nerves in GI tract

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27
Q

When and how to give antiemetics

A

Give 1st dose parenterally so will be absorbed
Give when natural vomiting reflex in excessive and not considered helpful e.g. pancreatitis

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28
Q

Phenothiazine tranquilizers (acepromazine) works how as an antiemetic and SE

A

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

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29
Q

What are some commonly used antiemetics

A

Phenothiazine tranquilizers (acepromazine)
Prokinetic drugs such as Metoclopramide
Serotonin antagonist
Maropitant

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30
Q

How does Metoclopramide (Reglan®) work as an antiemetic

A

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.

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31
Q

When and when not to use prokinetic drugs

A

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
Q

Serotonin antagonist as an antiemetic and when to use it

A

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
Q

How does Maropitant (Cerenia®) work as an antiemetic and when to use it

A

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
Q

How do anti-diarrheals work

A

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
Q

What are some classes of anti-diarrheals

A

Motility modifiers
Blocking secretions
Absorbants and protectants
Drugs that affect intestinal flora

36
Q

What drugs work as motility modifiers for diarrhea

A

Opioids/Opioid-Related Agents
Mu-receptor agonists

37
Q

How do Opioids work as motility modifiers for diarreha

A

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
Q

What anti-diarrehals block secretions

A

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
Q

How does blocking secretions work for anti-diarrheals

A

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
Q

What drugs stop Gi secretions

A

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
Q

How do absorbents and protectants work for diarrhea

A

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
Q

Adverse effects absorbents and protectants for diarrhea

A

Few adverse-effects
Take 1-2 hours after other oral drugs or may impair their absorption

43
Q

How does Bismuth subsalicylate (PeptoBismol®) work and when to avoid

A

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
Q

Types of absorbent and protectants for diarreha

A

Bismuth subsalicylate (PeptoBismol®)
- OTC/ELDU
Kaolin/pectin (Kaopectate®)
- OTC/ELDU
Barium
Activated Charcoal

45
Q

Barium is used when for diarreha

A

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
Q

Activated charcoal as a protectant for Gi tract

A

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
Q

Why would you use drugs that affect GI flora with diarrhea

A

Upset of regular GI flora is a cause of diarrhea and often secondary to other causes of GI inflammatio

48
Q

What drugs effect he intestinal flora

A

Metronidazole
Tylosin
Prebiotics
Probiotics

49
Q

Metronidazole works by and is used when

A

Most common antibiotic for diarrhea in SA
Very effective against anaerobes (Clostridia) and Giardia
S/e: v/d, neurological symptoms

50
Q

Tylosin is used in what

A

Most common in cattle/swine not horses

51
Q

Prebiotics are used when

A

Given to promote growth and survival of beneficial bacteria in the gut
Ex. Vit B12, folate, iron, specific sugars

52
Q

Probiotics are used when

A

Live, beneficial bacteria. Not a drug.
Anaerobic (use ASAP after exposing to air)
Ex. Prostora® (Iams), yoghurt with live cultures

53
Q

Laxatives, Cathartics and Purgatives do what

A

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
Q

Irritant laxatives are and used when

A

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
Q

Osmotic laxatives work how and side effects

A

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
Q

Examples of osmotic laxatives

A

Lactulose- sugar that is not absorbed by the intestines; draws water.
Milk of magnesia,
Epsom salts

57
Q

Bulk forming laxatives are and work by

A

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
Q

Emoilient laxatives are and work by

A

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
Q

Lubricants for the GI tract are and work by

A

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
Q

What drugs decrease stomach acid

A

Antacids
Histamine-2 Receptor Antagonists
Proton Pump Inhibitors

61
Q

How do antacids work

A

Buffers and alkalinizing agents
In the stomach and chemically neutralize pH of the gastric juice
TUMS®, Rolaids®

62
Q

Side effects of antacids

A

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
Q

Histamine-2 Receptor Antagonists decreases stomach acid by and when

A

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
Q

Proton pump inhibitors are used for and how do they work

A

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
Q

Mucosal Protectants as an antiulcer med are

A

Sucralfate (Sulcrate)

66
Q

Mucosal Protectants as an antiulcer med mechanisms

A

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
Q

Appetite stimulants are used when

A

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
Q

What are some common appetite stimulants

A

Cyproheptadine (Periactin®)
Diazepam

69
Q

When to use Cyproheptadine (Periactin®) as a appetite stimulant and side effects

A

Human anti-depressant; works in cats
S/e: aggression and excitement

70
Q

How to use diazepam as an appetite stimulant

A

Up to 4 doses max in cats; otherwise will increase risk of acute hepatotoxicity
Can give IV or PO

71
Q

What are some drugs that can treat bloat

A

Ruminatorics
Antifoaming drugs

72
Q

How do Ruminatorics work

A

Stimulate rumen motility by activating the PNS (ex. indirect-acting cholinergics)
E.g. neostigmine

73
Q

When and how to use antifoaming drugs

A

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
Q

Ionophores - Rumensin® are and used when

A

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
Q
A

Pharmocology (10 decks)

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