Core pharmacology

Class Group

H2 Receptor Antagonist

Legacy Cicm Level

-

Main Action

decreased gastric pH and decreased gastric secretions

Mechanism of action

MOA: Competitive antagonism of H2 receptors (high specificity) Histamine acts on GsPCR → increased AC → increased cAMP → increased protein kinase → increased activity of H/K antiporter

Physiological effects

GIT: Raised gastric pH. No effect on gastric emptying or LOS tone

CVS: Bradycardia and hypotension may occur after rapid injection (Cardiac H2-R)

CNS: confusion, hallucinations, seizures in renal impairment

Endocrine: gynaecomastia, impotence and decreased sperm count in men

Adverse Effects Toxicity

1. CYP inhibitor- decreased metabolism of warfarin, phenytoin, diazepam, TCAs
2. Increased VAP in critically ill

Absorption

Absorbed in small bowel
BA 60%

Distribution

Crosses BBB, placenta and breast milk

Protein binding

20% PB

Volume of distribution

Widely distributed throughout the body (most found in skeletal muscle)

Metabolism

50% Hepatic metabolism by CYP450

Excretion

50% excreted in urine unchanged

Half-life

T1/2= 1.5-2.5 hours