O2ii / 16B08: Compare and contrast the pharmacology of ranitidine and omeprazole
16B08: Exam Report
Compare and contrast the pharmacology of ranitidine and omeprazole.
14% of candidates passed this question.
These agents are both commonly used in the ICU. The expectation was weighted towards the interesting and important aspects of pharmacology as outlined for category B drugs. It was expected candidates could detail that both drugs are used to suppress acid secretion in the stomach. Ranitidine is a competitive, reversible inhibitor of the action of histamine at the histamine H2 receptors found in gastric parietal cells. This results in decreased gastric acid secretion and gastric volume, and reduced hydrogen ion concentration.
In contrast to Omeprazole which is a proton pump inhibitor that irreversibly blocks the hydrogen potassium ATPase the gastric parietal cells.
Some general description of dosing, route of administration, pharmacokinetics and possible adverse effects was expected.
O2ii / 16B08: Compare and contrast the pharmacology of ranitidine and omeprazole
Ranitidine
Omeprazole
Use
Ranitidine
PUD
Stress ulcer prophylaxis
GORD
Dyspepsia
Omeprazole
H.Pylori infection
PUD, GORD, Dyspepsia
Zollinger-Ellison syndrome
Upper GI bleed
Presentation
Ranitidine
Tablets
Clear solution injection – 25mg/mL
Omeprazole
Capsules – 40mg powder vial
Dose
Ranitidine
50mg QID (IV)
150mg BD (PO)
Omeprazole
40mg OD or BD (PO)
40mg OD or BD (IV)
MoA
Ranitidine
- Inhibits gastric acid secretion
- Competitive Antagonist (actually an I.A) of H2 receptors of PARIETAL CELLS, which secrete HCl & IF
- Histamine, ACh, gastrin cells stimulate Parietal cells but histamine most potent because:
- Blocks HCl secretion
- ↓volume of HCl secretion because ACh & gastrin action potentiated by histamine
Omeprazole
- ↓Gastric acid acidity
- Irreversibly binds H/K/ATPase pump of Parietal cells
- NON-COMPETITIVE INHIBITION
- Prevents H+ excretion
PD
Ranitidine
GI:
- Gastric acid secretion
- ↑LES tone (dose related)
Omeprazole
GI:
↓volume of gastric acid
PK
Ranitidine
A
OBA 60%
D
15% PPB, VD 1.2 – 1.8L/kg
M
small % metabolised by oxidation & methylation
E
mostly metabolised by kidneys
t ½ 1.6 – 2.5hrs
Omeprazole
A
OBA 75%; rapid in 30 min peaks
D
95% PPB, VD 0.4L/kg
M
hepatic by CYP450, almost completely
E
urinary, metabolites excreted
t ½ 1hr
S/E
Ranitidine
Abnormal LFTs
Thrombocytopaenia
Confusion
Omeprazole
Confusion
Blurry vision
Drowsy
Arrhythmias
- Author: Krisoula Zahariou