Flashcards in 77. H2 blockers Deck (14)
H2 blockers - names
Cimetidine, ranitidine, famotidine, nizatidine
H2 blockers - mechanism
Reversible block of histamine H2-receptors --> Decreased H+ secretion by parietal cells.
H2 blockers - clinica use
Peptic ulcer, gastritis, mild esophageal reflux.
H2 blockers - adverse effects
Cimetidine is a potent inhibitor of cytochrome P-450 (multiple drug interactions); it also has
antiandrogenic effects (prolactin release, gynecomastia, impotence, libido in males); can
cross blood-brain barrier (confusion, dizziness, headaches) and placenta. Both cimetidine and
ranitidine renal excretion of creatinine. Other H2 blockers are relatively free of these effects.
• Give at least two examples of H2 blockers.
Cimetidine, ranitidine, famotidine, nizatidine (take H2 blockers before you dine, & table for 2 to remember H2)
• What substance is the endogenous agonist of the H2 receptor?
• What is the effect of H2 blockers on parietal cells?
Reversible decrease of hydrogen ion secretion
• Name at least two clinical uses of H2 blockers.
Peptic ulcers, gastritis, mild esophageal reflux
• A patient takes over 10 medications for various reasons. You are worried about drug interactions. Which H2 blocker should you avoid?
Cimetidine, as it causes inhibition of cytochrome P-450 and may alter the metabolism of other drugs
• Which two H2 blockers can decrease the renal excretion of creatinine?
Ranitidine and cimetidine
• A 50-y/o man starts a gastritis medication that inhibits cytochrome P-450. What adverse effects for this drug are seen specifically in men?
Prolactin release, gynecomastia, impotence, decreased libido (cimetidine is a P-450 inhibitor and has antiandrogenic effects)
• A 47-year-old woman has developed confusion, dizziness, and headaches since starting an H2 blocker. What is happening?
Cimetidine (able to cross the blood-brain barrier, unlike other H2 blockers) can cause confusion, dizziness, and headaches
• A woman on a specific H2 blocker tells her doctor that she wants to get pregnant. The doctor says she needs to stop the H2 blocker. Why?
Cimetidine, the H2 blocker she is likely taking, is dangerous to the fetus, because it can cross the placenta