Misoprostol

Indications:

  • Gastric protection during therapy with NSAIDs
  • Therapeutic abortion (with the anti-progestogen agent mifepristone and usually methotrexate)
  • Can be used in induction of labour

Mechanism of Action:

Prostaglandin E (EP) receptor agonist. EP receptors are seven-transmembrane G-protein-coupled receptors.

Lecture and CAL materials: (under review)

Omeprazole

UNDER REVIEW (September 2016)

Mechanism of Action:

Proton pump inhibitor that blocks H+/K+ ATPase (proton pump) in parietal cells. Omeprazole is a pro-drug and a weak base which is inactive at neutral pH. It is activated in the acidic environment of the canaliculi of parietal cells and is usually enteric-coated to avoid premature activation. The active form binds covalently to sulphydryl groups in the proton pump, irreversibly inhibiting it. Under normal conditions, rises in cAMP and Ca2+ in parietal cells of stomach activate the proton pump which exchanges H+ in the cell with K+ in the lumen of the gastric gland. Proton pump inhibitors inhibit the process and so reduce gastric acid secretion very effectively. Its effects are evident for up 3 days because it stays in the canaliculi. To start acid secretion once again, new proton pumps have to be made, a process that takes about 18 hours. Proton pump inhibitors cause gastrin levels to rise – gastrin is a natural stimulator of acid secretion in the stomach, and levels of gastrin rise when acid levels are low.

Lecture and CAL materials:

Ranitidine

UNDER REVIEW (September 2016)

Mechanism of Action:

Ranitidine is a histamine H2-receptor antagonist. Histamine, released from enterochromaffin (mast-like) cells in the stomach, activates histamine H2 receptors (seven-transmembrane G-protein-coupled receptors) which promote acid secretion. Being a reversible competitor of histamine at H2 receptors on parietal cells, ranitidine prevents histamine-induced gastric acid secretion. It also indirectly inhibits gastrin- and acetylcholine-stimulated gastric acid secretion, which also results in reduced secretion of pepsin (digestive enzyme that hydrolyzes protein).

Lecture and CAL materials: