PreOp Meds: H2 antagonist concepts

Question 1

When are H2 antagonists most often utilized and what is their mechanism of action?

Answer 1

• Duodenal ulcer disease and GERD
• ↓ Gastric volume and ↑ gastric pH

Question 2

What side effect(s) is/are especially pertinent with long term H2 antagonist administration? Why does this occur?

Answer 2

• Bacterial overgrowth → pulmonary infections, weakened mucosa, and candida albicans.
• This bacterial overgrowth occurs from chronically alkalotic stomach fluid.

Question 3

What considerations should be given for renal patients when giving H2 receptor antagonists?

Answer 3

• Chronic H2 antagonist = creatinine ↑ by 15%

Question 4

What is the overall side effect list for H2 antagonists?

Answer 4

• Diarrhea
• Headache
• Skeletal muscle pain
• ↑ stomach bacteria
• HA, & confusion
• Bradycardia
• ↑ serum creatinine

Question 5

What CNS effects might be seen from H2 antagonist administration? When would this occur more often?

Answer 5

• Headache/confusion from CNS H2 receptors (occurs more in the elderly)

Question 6

What examples of H2 antagonists were given in lecture?

Answer 6

• Cimetidine
• Ranitidine
• Famotidine

Question 7

Which H2 antagonist strong inhibits CYP450’s?

Answer 7

• Cimetidine

Question 8

Describe cimetidine, ranitidine, and famotidine’s interactions with CYP450 enzymes.

Answer 8

• Cimetidine: strong CYP450 inhibition
• Ranitidine: weak/no CYP450 inhibition
• Famotidine: no CYP450 inhibition

Question 9

Histamine-2 receptor activation can mimic these other receptor types?

Answer 9

• 5-HT3
• β-1

Question 10

Histamine binding to H2 receptors generally elicits what effect?

Answer 10

• Stomach acid secretion
• ↑ cAMP (β-1 similar stimulation)

Question 11

What signs/symptoms occur with excessive H-1 & H-2 activation?

Answer 11

• Hypotension (from NO) release
• ↑capillary permeability
• Flushing
• Prostacyclin release
• Tachycardia