# H2 blockers and Anaphylaxis



## fma08 (Feb 10, 2009)

So this was brought up on another thread. A person said their medical director has them carrying Zantac for anaphylaxis on long transports. As I had understood it, Zantac is an H2 blocker. It was also my understanding that H2 blockers help with excess acid production in the stomach, and it was H1 blockers that were useful for allergy problems. Can anyone enlighten me on how blocking H2 can help with allergic reactions and anaphylaxis?


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## TransportJockey (Feb 10, 2009)

Your understanding of it seems to mirror what I was taught in Pharmacology last semester, I am kinda curious about it too.


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## Epi-do (Feb 10, 2009)

Here's what I found with a quick Google search.  Hope it helps.



			
				eMedicine said:
			
		

> Despite the potential contribution of multiple mediators, histamine infusion alone is sufficient to produce most of the symptoms of anaphylaxis. Histamine mediates its effects through activation of histamine 1 (H1) and histamine 2 (H2) receptors. Vasodilation is mediated by both H1 receptors and H2 receptors. H2 receptors exert a direct effect on vascular smooth muscle, whereas H1 receptors stimulate endothelial cells to produce nitric oxide. Cardiac effects of histamine are largely mediated through H2 receptors. H1 receptors are primarily responsible for extravascular smooth muscle contraction (eg, bronchial tree, gastrointestinal tract). Both H1 receptors and H2 receptors mediate glandular hypersecretion.





			
				eMedicine said:
			
		

> Histamine2-receptor antagonists
> These agents block effects of released histamine at H2 receptors, thereby treating vasodilation, possibly some cardiac effects, and glandular hypersecretion. H2 blockers with H1 blockers have additive benefit over H1 blockers alone in treating anaphylaxis. Ranitidine (Zantac) probably preferred over cimetidine (Tagamet) in anaphylaxis in light of the risk for hypotension with rapidly infused cimetidine and the multiple, complex drug interactions with cimetidine. Famotidine (Pepcid) IV is another good alternative.



You can read the entire article here


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## rhan101277 (Feb 11, 2009)

This was a good read, thanks for the post.


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