13.02.07 GI pharmacology

Clopidogrel + PPI Interaction

    • PPIs reduce the effectiveness of clopidogrel in preventing the recurrence of adverse cardiac events such as heart attack and coronary artery restenosis

Drugs increasing mucosal resistance

    • Physical barriers

      • Bismuth

      • Sucralfate

    • Prostaglandin analogues

      • Misoprostol

Antacids

    • Increase rate of emptying => Short effect

    • Stimulate gastrin release => Tolerance/adaptation

H. pylori eradication

    • Must have a PPI

    • Plus any two of:

      • Amoxicillin

      • Metronidazole

      • Clarythromycin

    • Doses vary depending on combination

    • Choose the ones patient hasn't taken recently

Management of constipation

    • Contraindications

      • Intestinal perforation or obstruction

    • Bulk-forming

      • Fybogel, Methylcellulose

    • Stimulants (NB abdo. cramps)

      • Anthraquinones

        • Senna

        • Co-danthramer (palliative only - ?carcinogenic)

      • Docusate sodium (dual effect)

      • Diphenylmethabe derivatives

    • Softeners (NB risk of incontinence)

      • Docusate sodium

      • Liquid parafin

    • Osmotic

      • Lactulose

      • PEG (Movicol)

      • Magnesium salts

      • Phosphate

Diarrhoea

    • Drug causes

      • Magnesium-containing antacids

      • NSAIDs

      • Lithium

      • PPIs

    • Treatment

      • Rehydration fluids MUST CONTAIN GLUCOSE for salt uptake

      • Generally no Abx

  • C. diff

      • Treat with oral metronidazole or vancomycin

    • Antimotility drugs

      • NEVER in anyone <12

Nausea + vomiting pathways

    • Chemoreceptor trigger zone

      • Dopamine + 5-HT3 serotonin receptor

    • Vestibular

      • Cholinergic muscarinic receptor

    • Vomiting centre pathways

      • Histamine + cholinergic muscarinic receptors

    • Gastric status

      • Dopamine + 5-HT4 serotonin receptor

Antiemetics

    • Metoclopramide

      • Dopamine D2 antagnoist

      • => Causes dystonia, esp. if <18 or >70

        • Can treat with procyclidine (anticholinergic)

    • Promethazine

      • 1st generation antihistamine

      • Safe in pregnancy (e.g. hyperemesis gravidarum)

      • Sedative effects

Crohn's remission

    • Yes

      • Azathioprine

      • Infliximab

      • Methotrexate

    • No

      • Aminosalicilates (but probably not harmful so often continued)

      • Cyclosporin (high risk of adverse events)

      • Corticosteroids (harm > benefit)

Stomach acid secretion

Notes

    • Metronidazole tastes bad

    • Beware antimotility drugs in UC

      • => Paralytic ileus + megacolon