Benadryl as antiemetic

[daedalus]

Hi folks. I am finishing up training as a paramedic in a system where we have zofran and liberal indications for giving it on standing orders. This has been wonderful and it is great to be able to see the results for nauseous patients in the field. I may take a job in a system without zofran and am wondering if any of you have standing orders for benadryl as an antiemetic. I cannot seem to find anything on google scholar that would point to its efficacy or lack of therefore for nausea and vomiting. Incidentally I have seen it as a protocol for RNs at a local ER for co-administration with morphine and dilaudid to prevent n&v.

[rock_shoes]

Diphenhydramine (Benadryl) "Antagonizes the effects of histamine at H1-receptor sites." In addition to reducing the net effect of a histamine release this mechanism of action also reduces nausea making Diphenhydramine an effective antiemetic. Like other anti-histamines however Diphenhydramine also causes CNS depression resulting in drowsiness.

Dimenhydrinate (Gravol) is a salt mix including Diphenhydramine and a stimulant (a derivative of Theophylline if I recall correctly). The stimulant in Gravol helps to counteract the CNS depressing effects of Diphenhydramine on its own (Neither does anything until disassociated in the body). Therefore the component of Dimenhydrinate that functions as an antiemetic is exactly the same as the active component of Diphenhydramine.

Zofran has a completely different mechanism of action which I suspect has something to do with why your medical director has chosen it over Diphenhydramine or one of its derivatives.

[daedalus]

Diphenhydramine (Benadryl) "Antagonizes the effects of histamine at H1-receptor sites." In addition to reducing the net effect of a histamine release this mechanism of action also reduces nausea making Diphenhydramine an effective antiemetic. Like other anti-histamines however Diphenhydramine also causes CNS depression resulting in drowsiness.

Dimenhydrinate (Gravol) is a salt mix including Diphenhydramine and a stimulant (a derivative of Theophylline if I recall correctly). The stimulant in Gravol helps to counteract the CNS depressing effects of Diphenhydramine on its own (Neither does anything until disassociated in the body). Therefore the component of Dimenhydrinate that functions as an antiemetic is exactly the same as the active component of Diphenhydramine.

Zofran has a completely different mechanism of action which I suspect has something to do with why your medical director has chosen it over Diphenhydramine or one of its derivatives.

rock_shoes, I understand the mechanism of both benadryl and zofran, and I understand why zofran is superior to benadryl for n&v. What I am looking for is some evidence of benadryl's antiemetic properties beyond the occasional "diphenhydramine is also a antiemetic" found across the web. I am also looking to see if anyone here has protocols that allow benadryl for nausea in their system.

[Levi]

rock_shoes, I understand the mechanism of both benadryl and zofran, and I understand why zofran is superior to benadryl for n&v. What I am looking for is some evidence of benadryl's antiemetic properties beyond the occasional "diphenhydramine is also a antiemetic" found across the web. I am also looking to see if anyone here has protocols that allow benadryl for nausea in their system.

Hey daedalus,

Diphenhydramine is the exact same chemical as dimenhydrinate. The latter just has an additional substance added to it to prevent (albeit poorly) drowsiness. The mechanism for diphenhydramine/dimenhydrinate is not well understood beyond the presence of some H1 receptors which are found in the vestibular apparatus of your inner ear, which would of course help to prevent motion-sickness. There may be H1 receptors found elsewhere in other parts of the brain, but nothing has been found yet. Zofran (Ondensentran) is a 5HT-3 receptor antagonist which is found directly in the area postrema of the brain (the vomiting centre), so it has a much more direct action.

[Eydawn]

Give DwayneEMTP a PM- he used diphenhydramine in Afghan-land when he was over there working with some Aussie docs and clued me in to its use when I was talking to him about some nasty food poisoning my husband was going through. Worked like a freakin' *charm* in concert with some dramamine...

Dwayne will have access to some actual protocols, probably.

Wendy

CO EMT-B

[Dustdevil]

Although I have used diphenhydramine as an antiemetic in a pinch, I have never worked any EMS system that had this written in protocol. We've always either had Phenergan and/or Vistaril as an option. I would be surprised if the system you are referring to, who does not use Zofran, did not have Phenergan, especially if they use morphine.

[DwayneEMTP]

Although I have used diphenhydramine as an antiemetic in a pinch, I have never worked any EMS system that had this written in protocol. We've always either had Phenergan and/or Vistaril as an option. I would be surprised if the system you are referring to, who does not use Zofran, did not have Phenergan, especially if they use morphine.

Actually, I got into a pissing contest with an Aussie (maybe NZ, I can't remember for sure now. (Ak, chicken shit Mike, where was he from?)) doc in Kandahar over this issue. We had one of our drivers begin to react to a new soap that he had showered with. Significant edema where the soap had touched, light headed, slight wheezing. I gained access in the clinic, gave 0.5 epi SQ and was just getting ready to push Benedryl (No oral option) when the doc reached out and stopped me saying, "No! That's for n/v, he needs Phenergan!" Now, I was fortunate that the medics didn't necessarily need to answer to the docs there, as well as having akflightmedic to cover my ass, so I pushed the Benedryl and all was well with the world in a few minutes.

We talked about it after, the doc and some of the rest of us, and it turns out that I was used to using Phenergan as an antiemetic and Benedryll for allergic reactions, yet the Aussies (NZ?) use them exactly opposite. (Perhaps because they're on the upside down side of the planet? Who can say.) I'd not really given any thought up to that point as to why we'd push one instead of the other, and am still not completely sure why. Benedryl and Phenergan were our two options there.

I don't have access to protocols that say that, but that is how it worked there. At this point I'm going to punt to ak as he's still working with the Aussies in that environment.

Dwayne

[Dustdevil]

I was used to using Phenergan as an antiemetic and Benedryll for allergic reactions, yet the Aussies (NZ?) use them exactly opposite. (Perhaps because they're on the upside down side of the planet? Who can say.)

ROFL!

[Levi]

Actually, I got into a pissing contest with an Aussie (maybe NZ, I can't remember for sure now. (Ak, chicken shit Mike, where was he from?)) doc in Kandahar over this issue. We had one of our drivers begin to react to a new soap that he had showered with. Significant edema where the soap had touched, light headed, slight wheezing. I gained access in the clinic, gave 0.5 epi SQ and was just getting ready to push Benedryl (No oral option) when the doc reached out and stopped me saying, "No! That's for n/v, he needs Phenergan!" Now, I was fortunate that the medics didn't necessarily need to answer to the docs there, as well as having akflightmedic to cover my ass, so I pushed the Benedryl and all was well with the world in a few minutes.

We talked about it after, the doc and some of the rest of us, and it turns out that I was used to using Phenergan as an antiemetic and Benedryll for allergic reactions, yet the Aussies (NZ?) use them exactly opposite. (Perhaps because they're on the upside down side of the planet? Who can say.) I'd not really given any thought up to that point as to why we'd push one instead of the other, and am still not completely sure why. Benedryl and Phenergan were our two options there.

I don't have access to protocols that say that, but that is how it worked there. At this point I'm going to punt to ak as he's still working with the Aussies in that environment.

Dwayne

That's hilarious...in addition to H1 blocking effects, both Benadryl and Phenergan have a lot of antimuscarinic properties. However, on top of THAT, Phenergan also has some alpha blocking properties, so it probably wouldn't be the best to use for someone at risk for developing anaphylactic shock. Only my opinion though; I'm sure the doc had his reasons for wanting promethazine.

[daedalus]

Thanks guys for all the input. Santa Barbara County EMS along with AMR in the same area ran a trial for zofran, and California decided to add it to the paramedic scope of practice because of its demonstrated efficacy in the trial. Unfortunately, as far as I can tell, the only county that has decided to bring Zofran on permanently was Santa Barbara itself. Most SoCal EMS systems are pretty resistant to change even if it means bringing on a drug with so few side effects and such potential to help suffering patients in the field.