r/pharmacology • u/nowlistenhereboy • Jun 14 '21

What is the reason why intravenous epinephrine must be diluted more than intramuscular in the setting of cardiac arrest?

Just curious what the physiological reason is that 1:1000 epinephrine is not to be used for cardiac arrest/active CPR.

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u/[deleted] Jun 14 '21

A more concentrate formulation allows for a smaller volume in muscle which is easier to administer.

A long slower infusion is required IV to reduce fatal hypertension, pulmonary and cerebral edema. For example 0.5ml of 1:10,000 IV for anaphylaxis is easier to administer safely than 0.05ml 1:1000. For cardiac events approx 10ml 1:10,000 is infused slowly which is safer and easier than 1ml 1:1000, especially when dose volume isn't a concern.

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u/JustHere2CorrectYou Jun 14 '21

Why do you reference 0.5ml of 1:10,000 IV, which would be 50mcg, for anaphylaxis? Are you talking about it as a push dose pressor? The IM treatment dose is 0.3-0.5mg, 50mcg is off by an order of magnitude.

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u/aswanviking Jun 14 '21

Not OP but in a patient with a pulse, 50 mcg of Epi rapid IVP is a relatively high dose.

IM doses are higher but get absorb slower and last longer.

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u/JustHere2CorrectYou Jun 14 '21

Right, so unless they’re peri-arrest I’m not sure why we’d even give a push dose of IV epi.

If you’re going to use IV epi for anaphylaxis it will usually be as a drip. I’m just not sure where the 50mcg IV push for anaphylaxis came from. The IM dose is much larger but absorbs slower and tapers itself overtime. If you’re going to us IV epi, you need a continuous infusion.

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u/aswanviking Jun 14 '21

Yeah fair. In theory, if you got central access, a little IV push epi (10-20 mcg) followed by drip would be quicker in onset and dose better adjusted to response.

But in non-ICU patients, just give It IM, it works surprisingly quickly.