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