Pharmacology- Gastrointestinal Drugs

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  1. Cimetidine
    Structurally similar to H with bulkier side chain - H antagonists. Inhibits basal acid secretion. ADR - diarrhea, headache, rash
  2. Loperamide
    • Opioid that doesn't cross blood/brain barrier (does not affect CNS). Reduces frequency of abdominal cramps and decreases muscle activity via myenteric plexus along with stimulating contraction of pyloric, Ileocolic and anal sphincters. Used commonly for travellers diarrhoea and inflammatory bowel conditions.
    • Highly selective action on GIT.
    • Contra indicated in children <2 due to paralytic ileus, and in patients suffering from bacterial infection.
    • ADR- Abdo pain, bloating, nausea, paralytic ileus.
    • Drug undergoes significant enterohepatic recycling.
  3. Ondansetron
    • CTZ  anti-serotonergic agent, also with peripheral actions. 
    • More effective when in combination with other anti emetics. Not considered effective in motion sickness 
    • ADR - headache and constipation. Use for post op nausea and nausea caused by drugs.
  4. 5-aminosalicylates (mesalazine)
    Anti-inflammatory agent that inhibits the COX and lipooxygenase pathways. Released in the colon due to the N=N bond being spit.
  5. Inflicimab
    Biological agent. anti TNF-alpha mAB.
  6. Promethazine
    • H antagonist present in the vestibular nuclei and nuclei of solitary tract.
    • Most effective as a prophylactic for nausea and vomiting. 
    • ADR= Drowsiness and sedation. Use for motion sickness and morning sickness. Should not be used in children/elderly due to risk of resp. arrest. 
  7. Metoclopramide
    • Acts centrally on the dopamine receptors, inhibiting smooth muscle relaxation.
    • Anti emetic, first line of choice in Alcohol abuse, radiation, GI disorders and cytotoxic drugs.
    • ADR= fatigue, insomnia and prolactin release.
  8. Hyoscine
    mACh antagonist - disrupts cholinergic transmission between the inner ear and the vestibular nuclus. ADR= dry mouth, blurred vision, urine retention. Use = motion sickness
  9. Nabilone
    Cannabinoid agonist. Used for emesis when other drugs aren't working.
  10. Opiates: Morphine/Codeine
    Inhibits aCh release from the myenenteric plexus and reduces motility to cause an overall increase in fluid and electrolyte absorption. ADR = respiratory depression and addiction.
  11. Ranitidine
    Structurally similar to H with bulkier side chain - H antagonists. Inhibits basal acid secretion. ADR - diarrhea, headache, rash
  12. Omeprazole
    • Proton pump inhibitor. Binds to HKATPase and inactivates it. Acide secretion only resumes when new pumps are synthesised.
    • ADR - minor - headache, abdominal pain, nausea, diarrhoea. Used in gastric/peptic ulcers.
  13. Dexamethasone
    Corticosteroid used for emesis induced by cytotoxic drugs.
  14. Bicodyl, Senna
    • Stimulant purgatives.
    • Senna: Stimualtes H20 secretion following mucosal contact, directly stimulating ENS.
    • Bicodyl:Stimulates sensory nerve endings causing colonic contractions and inhibition of water absorption. Given orally or by suppositry. ADR = care is needed as it both can cause powerful movements. Also be wary of issues regarding water and electrolyte balance.
    • Contraindicated in obstructive bowel conditions.
  15. Prednisone
    Anti-inflammatory. produces lipocortin-1 and inhibits the conversion of membrane phospholipids to arachiodonic acid. Used in inflammatory conditions. ADR = cushings, HPA axis issues (adrenal atrophy). Use in IBD
  16. Prochloroperazine
    • Acts centrally on dopamine receptors. Inactive in the gut and not effective against emetic stimuli originating there. 
    • Anti-emetic, indicated in migraines and vertigo, being effective against motion sickness.
    • ADR- Seizures, esp. in children. Neuroleptic malignant syndrome.
  17. Aprepitant
    • Substance P inhibitor. Effective in the prevention of nausea and vomiting associated with emetogenic chemotherapy.
    • ADR- Diarrhoea, Fatigue, dizziness (crosses BBB), hypersensitivity reactions.
    • Combination with serotonergic antagonist and dexamethasone effective (allows 50% reduction in dexa dosage). 
  18. Methylcellulose, Bran, sterculia, agar
    Bulk laxatives. Act on SI and LI, adding bulk to stool and sequestering H20. Indicated in Diarrhoea and colostomy. 12-72hr onset and duration and no ADR so long as introduced gradually.
  19. Saline purgatives, Lactulose
    Osmotic laxatives. Stimulate intestine to hold more water, softening stool via increased luminal pressure. Saline of hyperosmotic. Act on SI and LI with onset and duration 0.5-6hours.
  20. Docusate sodium
    Faecal softener. Acts like detergent, and is a weak stimulant of laxative action. Symptomatic treatemnt for constipation and anorectal conditions. Acts on SI and LI with onset and duration of 12-72hrs (rectally: 5-20mins). Patients advised to consume plenty of water to irrigate bowel.
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Pharmacology- Gastrointestinal Drugs
Pharmacology log book revision
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