GI Lect I

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Accelipse
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208962
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GI Lect I
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2013-04-01 12:02:55
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Pharmacology II Rutgers Antiemetics
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For Rutgers P2 students
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  1. Laxatives cause...
    evacuation of formed fecal material from rectum.
  2. Cathartics cause...
    evacuation of unformed, usually watery fecal material from the entire colon.
  3. Pectins, hemicellulose and mucopolysaccharides
    Dietary fibers fermented by colonic bacteria: Produce short chain fatty acids, and Increase bacterial mass
  4. Psyllium (Metamucil)
    Carboxymethylcellulose (Citrucel)
    Calcium polycarbophyl (Fibercon, Fiberall)
    •MoA:  promote retention of water in colon by increasing bulk and softness to facilitate transit

    •Latency time: 1 to 3 days (softening of feces)

    •Adverse effects:  Bloating
  5. Milk of Magnesia
    Magnesium sulfate, Magnesium citrate
    Sodium Phosphate (Fleet Phospho-Soda, Visicol)
    • Saline Laxatives 
    • •MoA: osmotic retention of
    • water that stimulates peristalsis

    • •Latency time: 1 to 3 hours (watery
    • evacuation)

    • •Adverse effects:
    • -Magnesium: Electrolyte disturbances (Avoid
    • in certain patients: renal or cardiac dz,
    • diuretics)

    • –Phosphate: Acute nephropathy (Avoid
    • in certain patients: bowel or kidney dz,
    • ACEI, ARB, NSAIDS)
  6. Lactulose (Cephulac): synthetic disaccharide
    Sorbitol, mannitol: non-absorbable sugars
    Propylene glycol-electrolyte solution (GoLYTELY, Colyte, MiraLAX)
    •MoA: Stimulate colonic propulsive motility by drawing water into the lumen

    •Latency time: 1 to 2 days (lactulose, sugars)

    • •Adverse effects: Abdominal discomfort
    • or distention and flatulence, poor taste (mask with fruit juice)
  7. Lactulose
    • •Treat severe constipation. Also used for treating hepatic encephalopathy in patients with severe liver disease that have an impaired capacity to detoxify ammonia coming from the colon (produced by
    • bacteria metabolizing fecal urea)

    •Lactulose reduces luminal pH because of hydrolysis of short-chain fatty acids which “traps” ammonia and converts it to polar ammonium ion

    •Lowers circulating ammonia levels
  8. Bisacodyl (Dulcolax)
    Stimulant Laxative

    • –Activated in the bowel by hydrolysis from esterases
    • –Take whole to prevent stomach activation

    •MoA:  Unclear, low-grade inflammation in bowel that promotes water accumulation and stimulate intestinal motility

    •Latency time: 6 to 8 hours (soft or semifluid stool), faster if use bisacodyl suppository
  9. Senna (Ex-Lax, Senokot)
    Cascara sagrada
    Rhubarb and aloe
    • Stimulant Laxatives
    • –Long-term use causes benign pigmentation of colon mucosa

    •MoA:  Unclear, low-grade inflammation in bowel that promotes water accumulation and stimulate intestinal motility 

    •Latency time: 6 to 8 hours (soft or semifluid stool), faster if use bisacodyl suppository
  10. Docusates (Colace)
    Poloxamers
    Dehydrocholate
    Mineral Oil
    Stool-Wetting Agents

    •MoA: lower surface tension of the stool to allow mixing of aqueous and fatty substances, softening the stool and permitting easier defecation. May also stimulate intestinal fluid. 

    •Latency time: 1 to 3 days (softening of feces)

    •Adverse effects: mineral oil may impair absorption of fat-soluble substances (vitamins)
  11. Alvimopan (Entereg)
    •Purpose: Accelerate the time to upper and lower gastrointestinal recovery following partial large or small bowel resection surgery with primary anastomosis (surgical  connection between two hollow organs)

    –Off label use for opioid-induced constipation

    • •Mechanism: Oral, peripherally-acting, mu-opioid receptor (PAMOR) competitive
    • antagonist

    •PK: active metabolite, low systemic bioavailability (6%), Pgp substrate

    •Side effects: flatulence, hypokalemia, dyspepsia, anemia, urinary retention, diarrhea
  12. Methylnaltrexone (Relistor)
    • •Antagonist
    • of peripheral mu opioid receptor

    • –Used to treat opioid-induced constipation
    • (Methylnaltrexone, SC)

    –Also used to treat postoperative ileus

    •Only works in periphery and does not alter analgesia or cause withdrawal
  13. Dexpanthenol (Ilopan)
    • Tx Post-Operative Ileus
    • •Alcohol form of panthothenic acid (Vitamin B5) that is converted to coenzyme A internally

    •Coenzyme A increases synthesis of ACh by choline acetyl transferase
  14. Bethanechol 
    Metoclopramide Domperidone 
    Metoclopramide 
    Erthyromycin
    Prokinetic Drugs

    •Uses: treat GERD, gastroparesis, nightime heartburn, severe constipation

    •Purpose:  Enhance transit of materials thru GIT by direct activation of receptors that regulate motility

    •Goal: Increase cholinergic stimulation of enteric nerves

    • Muscarinic M2/3?
    • Dopamine D2
    • Serotonin 5HT4
    • Motilin Receptor
  15. Loperamide
    •Mu opioid receptor agonist

    • •Increases anal sphincter tone
    • •Poor CNS penetration
    • •OTC in multiple forms

    • •Overdose:
    • –CNS depression (children)
    • –Paralytic ileus
  16. Diphenoxylate/Difenoxin
    •Mu opioid receptor agonists

    •Diphenoxylate is ester of difenoxin

    • •Some CNS penetration
    • –Abuse potential
    • –Include small doses of atropine to discourage abuse

    • •High doses:
    • –Constipation
    • –Toxic megacolon (if inflammation)
    • –Anticholinergic effects
  17. Camphorated Opium Tincture
    •Contains the equivalent of 0.4 mg/ml morphine

    •Dose: 5 to 10 ml

    •AKA Paregoric
  18. Deodorized Tincture of Opium
    •Contains the equivalent of 10 mg/ml morphine

    •Dose: 0.6 ml
  19. Bismuth Subsalicylate
    •Indications: episodic diarrhea, acute gastroenteritis, treatment of Helicobacter pylori infection, also helps with abdominal cramps and nausea, Traveler’s diarrhea

    •MoA: Unclear, may have anti-secretory, anti-inflammatory, and antimicrobial effects

    • – At low pH of stomach, BSS reacts with HCl to form bismuth oxychloride and salicylic acid
    • – Salicylate absorbed by stomach and SI; Bismuth not absorbed
    • – Coats ulcers and erosions, bind enterotoxins

    • •Adverse effects:
    • –Dark stools – not melena or harmful
    • –Black tongue (reaction of bismuth sulfide); not harmful
    • –Reye’s syndrome in children
  20. Octreotide (Sandostatin)
    •Type: Synthetic sc/iv octapeptide analog of somatostatin

    • •Mechanism/Use:  Inhibits severe secretory diarrhea due to hormone-secreting tumors of the pancreas and GIT by blocking release of
    • hormones
    • –5HT, gastrin, insulin, secretin, vasoactive intestinal polypeptide

    • •Off-label uses: Diarrhea due to… 
    • –Chemotherapy
    • –HIV
    • –Diabetes
    • –“Dumping syndrome” after gastric surgery.  Octreotide will inhibit release of hormones triggered by rapid passage of food into SI

    •Similar new drug: lanreotide (Somatuline) – SR formulation
  21. Kaolin, pectin, attapulgite
    OTC Products for Diarrhea

    –Clays used for their absorbent and protective action

    –Bind water and may bind enterotoxins

    –Nonselective binding: may remove Rxs and nutrients

    •Avoid within 2-3 h of Rxs
  22. Traveler’s Diarrhea
    •Symptoms: 3 or more loose stools in 24 h by a traveler along with abdominal cramps, nausea and bloating

    •Cause: E.coli

    • •Treatment: Loperamide alone or in
    • combination with an antimicrobial agent
    • –Trimethoprim 
    • –Trimethoprim-sulfamethoxazole 
    • –Fluoroquinolone
  23. C. difficile Diarrhea
    •Pseudomembranous colitis or antibiotic-associated diarrhea (clindamycin, β-lactams, quinolones) most commonly caused by  Clostridium difficile

    •Symptoms: diarrhea, fever, abdominal pain, toxic megacolon (severe cases)

    • •Treatments:
    • –Vancomycin (PO): cell wall synthesis inhibitor, no PO abs’n, relapses possible

    • –Metronidazole (Flagyl, PO or IV): electron
    • transport interference (potential for  disulfiram reaction with alcohol)

    –Fidaxomicin (Dificid, PO): protein synthesis inhibitor (g+), no PO abs’n, approved in 2011

    • –Lactobacillis probiotics (adjunctive
    • therapy): controversial use
  24. Ondasetron (Zofran): t½ is 4 h
    Granisetron (Kitryl, Sancuso): t½ is 9-12 h
    Dolasetron (Anzemet): t½ is 7-9 h
    Palonsetron (Aloxi): t½ is 40 h, highest affinity for 5HT3 receptor
    5HT3 Antagonists

    •Serotonin signaling:

    –5HT3 receptors at vagal afferent nerves, the solitary tract nucleus (receives signals from vagal nerves), and area postrema

    –5HT3 is released by enterochromaffin cells of SI in response to chemotherapeutic drugs and stimulate vagal afferent via 5HT3 receptors to initiate vomiting reflex

    Antiemetic effects persist after drug clearance from circulation suggesting continued interaction at receptor.

    Well-tolerated
  25. Metoclopramide (Reglan)
    Trimethobenzamide (Tigan)
    • D2 Receptor Antagonists
    • Substituted benzamides

    “General purpose” anti-nauseants and anti-emetics
  26. Dronabinol, Nabilone
    Cannabinoid receptor agonists

    • Tx cytotoxic drug induced emesis
    • Also used to stimulate appetite in AIDS patients
    • Sympathomimetic activity and euphoria
  27. Cyclizine, Meclizine, and Hydroxyzine
    • Antihistamine H1 receptor antagonists
    • Tx Motion sickness
  28. Hyoscine (scopolamine)
    • Muscarinic receptor antagonists
    • Tx Motion sickness
  29. Aprepitant (Emend)
    • Neurokinin receptor antagonists
    • Tx cisplatin-induced delayed emesis (delayed phase - days 2 to 5)
    • Prevents substance P neuropeptide binding to NK1 receptors in the brain
  30. Lorazepam and Alprazolam
    • Benzodiazepines
    • Not good anti-emetics, but can help with anticipatory part of nausea and vomiting
  31. Emetrol
    • Phosphorated carbohydrate solutions
    • OTC solution of glucose, fructose and phosphoric acid
  32. Alosetron (Lotronex)
    • 5HT3 antagonist
    • Use: Treat diarrhea-predominant IBS
    • Concerns of severe constipation and ischemic colitis
    • Restricted prescribing with lower initial doses (women)
  33. Tegaserod (Zelnorm)
    • 5HT4 agonist
    • Use: Treat constipation-predominant IBS Increase GI motility, increase gastric secretions, and decrease visceral sensations
    • Restricted use in 2007 (women)
    • Concerns of ischemia (MI, cerebrovascular accident, unstable angina)
  34. Lubiprostone (Amitiza)
    • Chloride Channel Activator
    • Use: Treat constipation-predominant IBS
    • MoA: Activates CIC-2, a chloride channel present in the apical membrane of the intestine in a protein kinase A-independent fashion, thereby increasing secretion of chloride-rich intestinal fluid. This in turn increases intestinal motility and bowel movements within 24-48 h
    • PK: Low systemic availability
    • Side effects: Nausea, diarrhea, headache, abdominal distension and pain, flatulence
  35. Linaclotide (Linzess)
    • Guanylate cyclase-C agonist
    • Use: Treat constipation-predominant IBS and chronic idiopathic constipation
    • MoA: 14 amino acid peptide (and metabolite) activate guanylate cyclase C on the apical epithelial surface which increases intracellular and extracellular cGMP. This increases secretion of chloride and bicarbonate by the CFTR ion channel which increases intestinal fluid and GI transit
    • PK: Low systemic availability
    • Side effects: Diarrhea, abdominal pain, flatulence
  36. Dicyclomine (Bentyl), Hyoscyamine (Levsin)
    • Antispasmodics 
    • MoA: Non-specific antagonists of muscarinic receptors
    • Used on an as-needed basis (with onset of pain) or before meals to prevent pain and fecal urgency that occurs predictably in some IBS patients
    • Tertiary amines
  37. Glycopyrrolate (Robinul), Methscopolamine (Pamine)
    • Quaternary ammoniums
    • Antispasmodics 
    • MoA: Non-specific antagonists of muscarinic receptors
    • Used on an as-needed basis (with onset of pain) or before meals to prevent pain and fecal urgency that occurs predictably in some IBS patients
  38. Alpha-galactosidase (Beano)
    • Anti-flatulence
    • Hydrolase enzyme that breaks down polysaccharides and oligosaccharides
  39. Simethicone (Mylicon, Gas-x)
    • Mixture of siloxane polymers stabilized with silicon dioxide
    • Collapses bubbles by forming a thin layer of their surface
    • “Anti-foaming” agent

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