Week 21 Pharmacology


  • Weak bases that react with gastric acid to neutralise –> salt + water
  • Effect varies depending upon – rate of dissolution, water solubility, rate of reaction with acid, rate of gastric emptying
  • Sodium bicarbonate –> CO2 –> belching, abdo distention, potential metabolic alkalosis
  • Calcium carbonate
  • MgOh, AlOH – no CO2 so no belching, metabolic alkalosis uncommon. Can cause diarrhoea(Mg) or constipation(Al)
  • Renally excreted


H2 antagonists:

  • Cimetidine, ranitidine, nizatidine
  • PK – rapidly absorbed, first pass metabolism, 50% bioavail, t 1/2 1-4hrs, hepatic metabolism, glomerular filtration and tubular secretion
  • PD – competitve inhibitors of parietal cell H2 receptors –> supress basal and post prandial acid secretion in a dose dependent manner, esp nocturnal acid secretion. Volume of gastric acid secretion and pepsin is reduced. Inhibit secretion via histamine and by direct gastrin or ACh. Block 60-70% acid secretion in 24hrs.
  • Uses – GORD, PUD, dyspepsia
  • SE – diarrhoea, headache, fatigue, myalgias, constipation
  • Cimetidine inhibits binding of dihydrotestosterone to androgen receptor and inhibits metabolism of estradiol, increases prolactin –> gynaecomastia, impotence, gallactorrhoea. It also inhibits some Cyt P450.



  • Esomeprazole, omeprazole, pantoprazole, rabeprazol
  • PK – Admin as oral prodrug that is absorbed in intestine, lipophilic, weak bases, food decreases bioavail to 50% so give on empty stomach, t 1/2 1.5 hrs, rapid first pass and systemic hepatic metabolism, negligible renal clearance, long duration of action.
  • PD – activated in parietal cell canaliculus –> inhibits H+/K+ ATPase irreversibly when they are active. Block 90-98% acid secretion.
  • SE – diarrhoea, headache, abdo pain, reduce B12 abs, ? Dec Ca abs



  • Metoclopramide.
    • Dopamine2 receptor blockade
    • Centrally in chemoreceptor trigger zone in medulla – potent antinausea and antiemetic
    • Peripheral D2 block – Prokinetic- increase oesophageal peristalsis, enhance gastric emptying. No effect on small intestine or colonic motility.
    • SE – EPS, dystonia, restlessness, parkinsons
  • Prochlorperazine.
    • Antipsychotic agents, antiemetic and sedative(H)
    • PD – inhibit D and musc receptors.
    • SE – EPS, hypotension, antimuscarinic effects
  • Ondansetron
    • 5HT receptor antagonist centrally in vomiting centre and chemoreceptor trigger zone but mainly peripherally on intestinal vagal and spinal afferent nerves
    • Good for vomiting from vagal stimuli or post op or chemo, not very good at motion sickness(no effect on D or musc receptors, not pro motility)
    • PK – T1/2 4-9hrs, hepatic metabolism and eliminated by renal and hepatic excretion
  • Steroids


Passing familiarity with laxatives & anti-diarrhoeals;

(we don’t see these as viva questions)

  • Bulk forming – psyllium
  • Stool softener – docusate, glycerin
  • Osmotic – lactulose
  • Stimulant – senna
  • Antidiarrhoeal – opioids – loperamide


Familiarity with Antiseptics


Viva questions:

  • What agents can be used in the treatment of peptic ulcer ?
  • Tell me about omeprazole
  • Tell me about Ranitidine
  • What drugs have an anti-emetic action ?
  • Tell me about metoclopramide
  • Tell me about prochlorperazine
  • Tell me about ondansetron
  • Tell me about methods of disinfection and antiseptics