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GI Exam 3 > Lower GI pharmacology > Flashcards

Lower GI pharmacology Flashcards

1
Q

Drugs that primarily affect motility

A
  1. Enhance/disrupt afferents (5HT)
  2. Affect interneurons (DA, enkephalins)
  3. Efferent neurons of circular muscle (ACh)
  4. Affect muscle cells (motilin)
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2
Q

Afferent neurons of peristaltic reflex

A
  • stimulated by 5HT released from enterochromaffin cells which as sensory receptors
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3
Q

SSRIs

A

Fluoxetine, Paroxetine, Sertraline

  • most beneficial in constipation IBS
  • decrease reuptake of 5HT into EC cells -> increase 5HT in synapse -> increased afferent activity -> increased peristalsis
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4
Q

Bulk Laxatives

A

Fiber, methylcellulose, polycarbophil, psyllium
- attract water and increase mass of stool -> increased distention of lumen -> increase release of 5HT from EC cells -> increased peristalsis
“STOOL STABILIZERS”
- diarrhea = decrease BM, solidify stool, decrease pain
- constipation = increase BM, loosen stool, decrease pain
S.E. = allergies, flatulence, obstruction

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5
Q

Limits of bulk laxatives

A
  1. need neurons to be functional

2. cause of constipation must be known

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6
Q

Contact cathartics

A

Anthraquinone (act on large intesine-> less potent), Bisacodyl (prodrug), Castor Oil (acts on both small and large intestine -> potent)
- mechanism is thought to be dependent on enteric nervous system -> possible irritation increases EC cell activity
S.E. = dependency and destroy myenteric plexus
- pigmentation of mucosa
CASTOR OIL -> dehydration and electrolyte imbalances and uterine contractions

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7
Q

5HT3 receptor antagonists

A

Alosetron
- blocks 5HT3 receptor -> decreases afferent tranmission -> decreases peristalsis
- used for diarrhea IBS when nothing else works (restricted availability)
S.E. = constipation (BAD), hospitalization, ischemic colitis
- interaction with CYP1A2

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8
Q

5HT4 receptor agonists

A

Cisapride (prokinetic), Tegaserod (more selective)
- agonist 5HT4 receptor -> increase release of NT from afferent -> increased peristalsis
- used when nothing else works
Tegaserod -> constipation IBS
Cisapride -> diabetic gastroparesis
S.E. = CV toxicity (arrhythmia and long QT)

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9
Q

Enkephalins

A

interneurons -> ENK inhibit both contraction and relaxation -> so these drugs are inhibiting the inhibitors`

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10
Q

Opiates

A

Diphenoxylate (BBB), Loperamide (no BBB) (antidiarrheals)
- inhibit motility and secretion
- combine diphenoxylate with atropine because it blocks muscarinic receptors to decrease contractions
- most effective antidiarrheals
S.E. = ab cramps, toxic megacolon -> UC, euphoria

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11
Q

Mu receptor antagonists

A

Alvimopan (short term hospital), Methylnaloxone (long term palliative)
- don’t cross BBB -> just work in gut, given at time of opiate administration
- used for patients on opiates for pain
S.E. = Alvimopan -> increase risk of MI

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12
Q

Dopamine D2 receptor antagonists

A

Domperidone (no BBB), Metoclopramide
- cholinomemetics -> increase ACh actions -> inhibit DA inhibition ==> increase motility of entire gut (prokinetic)
- D -> compassionate use only -> impaired GI motility
- M -> antimemetic
S.E. = somnolence, nervousness, agitation, anxiety, dystonia, Parkinsonism, tardive dyskinesia, increased prolactin

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13
Q

Acetylcholine

A

RULE -> drugs directly affecting cholinergic nerves are NOT used for diarrhea
EXCEPTION -> TCA and Atropine

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14
Q

TCA

A

Amitriptyline, Desipramine

  1. decrease reuptake of NE from postganglionic sympathetics -> increased activation of alpha2 on presynaptic terminals of cholinergic postganglionic parasympathetics -> decrease ACh release -> decreased motility
  2. decrease reuptake of DA -> increase activation of D2 receptors -> decrease ACh and decrease motility
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15
Q

Atropine

A

direct anti-muscarinic effects –> decrease peristalsis

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16
Q

Motilin

A

macrolides –> erythromycin

  • stimulate motilin receptors on smooth muscle –> initiation of migrating motor complex
  • subclinical doses work but increase risk of resistant bugs
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17
Q

Newest treatments for diarrhea and constipation?

A

directed toward transporters responsible for chloride secretion in colon

18
Q

CIC-2 stimulants

A

Lubiprostone
- activates CIC-2 -> increased Cl secretion
- it’s poorly absorbed which is good -> no systemic effects
- used for chronic constipation and constipation IBS
S.E. = diarrhea, nausea, headache, increased fetal loss (class C drug)

19
Q

GC-C activator

A

Linaclotide
- activates guanylyl cyclase C -> increase cGMP -> activates CFTR -> increased Cl- secretion -> increased water in lumen
- poorly absorbed -> good
- used for chronic constipation and constipation IBS
S.E. = diarrhea, increased pregnancy maternal death (C), increased mortality in juvenile mice -> no pediatrics

20
Q

CFTR inhibitor

A

Crofelemer

  • voltage independent inhibition of CFTR -> decreased Cl secretion -> decreased water in lumen -> firm stool
  • poorly absorbed -> good
  • used for diarrhea due to anti-HIV treatment
21
Q

Somatostatin analog

A

Octreotide

  • synthetic analog -> longer t1/2 (6-12 hrs)
  • decreases fluid secretion
  • increases motility (low dose), decreases motility (high dose)
  • used for severe diarrhea (dumping, short-bowel, vagotomy, AIDS)
  • S.E. = impaired pancreatic secretions -> fat malabsorption & vitamins, decreased GI motility, decreased gallbladder contractility -> gall stones
22
Q

Bismuth Subsalicylate

A

direct antimicrobial activity -> binds enterotoxins
- Bismuth = stimlates PG, mucous, HCO3 secretion in stomach
- Subsalicylate - inhibits PG and Cl in colon
- used for diarrhea -> prophylactically
S.E. = blackening of stool (Bismuth), tinnitus (subsalicylate)

23
Q

Osmotic Cathartics

A

Lactulose, Magnesium Hydroxide, Sodium Phosphate, Polyethylene glycol
- increase water and electrolyte [ ] in colon -> mostly by osmosis
- used for constipation when enteric nervous system is compromised
- Lactulose -> decreases plasma ammonia [ ]
S.E. = if absorbed systemically -> intravascular volume depletion and electrolyte imbalances

24
Q

Bile acid binding resins

A

Cholestyramine, colestipol
- complex with bile salts -> decreased water secretion
- used for ileum diseases (Crohn’s, surgical resections)
S.E. = bloating, flatulence, constipation, fat malabsorption & vitamins

25
Q

Stool softeners

A

Docusate -> surfactant -> allows mixing of aqueous and fatty substances
Mineral Oil -> lubricates feces -> decreases water absorption
- widespread use but only moderate efficacy in constipation
S.E. = mineral oil can cause lipid pneumonitis if aspirated

26
Q

Prokinetics

A

D2 antagonists, macrolides, 5HT4 agonists
dramatically increase motility throughout entire GI tract
- used for impaired gastric emptying (vagotomy and diabetic gastroparesis)

27
Q

Antidiarrheals

A

don’t use with bloody diarrhea or fever

- Opiates, BABR, octreotide, bismuth, crofelemer, absorbants

28
Q

5HT3 antagonists

A

anti-emetics –> DolaSETRON, GraniSETRON, OndanSETRON, PalonoSETRON
- blockade of peripheral 5HT3 receptors on intestinal vagal afferents
- primary agents for preventing/treating chemo induced N/V
- most effective when given 30 mins before chemo
S.E. = excellent safety except Alosetron, headache, dizziness, constipation

29
Q

Anticholinergics

A

Scopolamine –> anti-emetic

  • inhibition of muscarinic receptors in cerebellum –> rapidly and fully distributed to CNS
  • partially effective for motion sickness -> give as transdermal patch (less S.E.)
30
Q

Neurokinin Receptor 1 Antagonists

A

Aprepitant (oral), Fosaprepitant (IV)

  • substance P is preferred ligand for NK, tachykinin receptor (antagonist the NK1 receptor)
  • used for prevention of acute and delayed chemo-induced N/V
  • given with 5HT3 antagonist and Dexamethasone
  • well tolerated, but CYP3A4 –> drug interactions
31
Q

Antihistamines (H1)

A

Dimenhydrinate, Diphenhydramine, Meclizine
- H1 blockers –> cross BBB (sedation)
- efficacy is increased with ephedrine or amphetamine
S.E. = anticholinergic, teratogenic ?, drug-interactions

32
Q

Dopamine D2 antagonists

A

Droperidol, Metoclopramide, Prochlorperazine, Promethazine, Thiethylperazine
- inhibition of D2 receptors and muscarinic receptors in CTZ –> causes sedation

33
Q

Cannabinoids

A

Dronabinol, Nabilone
- mechanism not well understood –> acts on central cannabinoid receptors
S.E. = euphoria, dysphoria, sedation, hallucinations, dry mouth, increased appetite

34
Q

Corticosteroids

A

Dexamethasone, Methylprednisolone

  • unknown mech for why they work
  • combine with 5HT3 receptor antagonists
35
Q

Aminosalicylates

A

Balsalazide, Mesalamine (5-ASA), Olsalazine, Sulfasalazine
- blocks PG synthesis by inhibiting COX pathway –> reduces inflammation
- B, O, S -> limited absorption until bacteria break it down
- used as first line treatment for mild/moderate UC –> not for Crohn’s
S.E. = well-tolerated, nausea, headaches, arthralgias, sensitivity

36
Q

Sites of action of Aminosalicylates

A 
Jejunum - Rectum = 5-ASA
Ileum to Rectum = 5-ASA pH dependent
Prox Colon to Rectum = Balsalazine, Sulfasalazine
Distal Colon to Rectum = 5-ASA enema
Rectum = 5-ASA suppository
37
Q

Corticosteroids

A

Budesonide, Prednisone, Prednisolone

  • used for treatment of moderate/severe IBD
  • Budesonide = extensive first pass metabolism –> local rather than systemic effect –> used for Crohn’s disease involving ileum and proximal colon
38
Q

Antimetabolites

A

Azathioprine, 6-Mercaptopurine, MTX

- given in low doses for induction and maintenance of remission of UC and Crohn’s

39
Q

Anti-TNF alpha

A

Infliximab (chimeric)
- dysregulation of Th1 response occurs in IBD (TNF alpha is major proinflammatory cytokine)
- antibody to bind solute and receptor bound TNF alpha –> no binding to cytokine –> no inflammation
- can lead to symptomatic improvement and remission of Crohn’s disease
S.E. = infection, pruritis, fever, chills, urticaria, lymphoma

40
Q

Monoclonal antibodies

A

Natalizumab –> targets alpha4 subunit of integrin

  • prevents integrins from binding selectins on vascular endothelial cells
  • used for Crohn’s when all else has failed
  • stop tx with anti-TNF’s 2 months before starting Natalizumab

GI Exam 3 (10 decks)

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