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  1. #1
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    Default benadryl contraindicated in asthma/ Why?

    I wanted to know why benadryl is contraindicated in asthma. What is the mechanism that causes an astmatic to have a problem with benadryl? This is purely a curiosity question as the subject came up when we were reviewing a test question for a medic student. It is in our protocol to not give it and we could find online a lot of resources that cited that it is contraindicated. We want to know "why". Thanks for your input.

  2. #2
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    Other than the obvious constriction caused by asthma, another effect is a decreased ability to clear mucus. Since benadryl has a drying effect to the airway, it's possible to essentially "plug up" an asthmatic by making the mucus thicker. I know it's a simple response, and it could be wrong, but that's the way I understood it when explained to me.

  3. #3
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    Diphenhydramine has many atropine-like (anticholinergic) side effects including the already-mentioned mucus problems (although atropine is a bit of a bronchodilator--you've probably seen its daughter compound ipratropium used as such--and it would not surprise me to learn that Benadryl is too, which may offset the reduced mucus). However, a single dose or two of Benadryl for an allergic reaction shouldn't be a problem.

    These folks say it's because of the sedating effect and would only really be contraindicated during an asthma attack. I guess it could mess up your physical exam, i.e. is the patient becoming drowsy because of the Benadryl, or because he's getting CO2 narcosis and is about to have respiratory failure? But if an asthmatic was having a life-threatening allergic reaction, I wouldn't hesitate to give it.
    Disclaimer: dr-exmedic is just a resident. Give him a break.

  4. #4
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    But if an asthmatic was having a life-threatening allergic reaction, I wouldn't hesitate to give it.
    that's the way I see it too.

  5. #5
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    Quote Originally Posted by FFmedic13 View Post
    Other than the obvious constriction caused by asthma, another effect is a decreased ability to clear mucus. Since benadryl has a drying effect to the airway, it's possible to essentially "plug up" an asthmatic by making the mucus thicker. I know it's a simple response, and it could be wrong, but that's the way I understood it when explained to me.
    Quote Originally Posted by dr-exmedic View Post
    Diphenhydramine has many atropine-like (anticholinergic) side effects including the already-mentioned mucus problems (although atropine is a bit of a bronchodilator--you've probably seen its daughter compound ipratropium used as such--and it would not surprise me to learn that Benadryl is too, which may offset the reduced mucus). However, a single dose or two of Benadryl for an allergic reaction shouldn't be a problem.

    Thats what I understand as well, but this is hardly an issue in an emergent situation. I wouldnt even put this in the area of Relative contraindication, but simply in the area of "special considerations".

    Given plenty of benadryl to Asthmatics with no acute issues. My Ex wife would have a little increased wheezing at night on Benadryl, but nothing significant either.
    Steve

    Paramedic, CCEMT-P, Geek

    "Boldness is like a condom. If you depend on it all the time, no matter how good it is, and no matter how good you are, eventually it will break. "

    "Personally, I believe that if we write our CE, text books, and curricula at the physician level instead of the kindergarten level, our medics and EMTs will rise to the occasion and meet the higher standard....."



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  6. #6
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    Jul 2007
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    Some have mentioned the anticholinergic effects of benadryl. Another mentioned that his ex-wife would experience some mild weezing after using benadryl. Most regional protocols have seperate protocols for asthma and anaphylaxis. Benadryl would not be indicated for a straight up asthma attack, if not contraindicated altogether. In my dept, reactive airway disease patients get an albuterol/ipatropium ****tail, then solu-medrol, mag, and epi if they're ctd, depending on asthma vs copd. For an allergic reaction, we give benadryl for a local skin reaction. If the reaction becomes systemic, such as airway/hypoperfusion issues, the pt will also get epi, solu-medrol, and albuterol. My point is, you always need a clear reason to give a med, as most meds have the potential to kill. Remember, all that wheezes is not asthma(pulmonary edema, anaphylaxis, pneumonia, partial airway obstruction, etc). Before you go into your drug box, please make sure that you can validate your intervention. Don't give the attorney anything to work with.

  7. #7
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    You completely misunderstood the thread. It wasnt "I want to give Benadryl to an asthmatic for asthma". It was " I want to give benadryl to an asthmatic who is having an allergic reaction".
    Steve

    Paramedic, CCEMT-P, Geek

    "Boldness is like a condom. If you depend on it all the time, no matter how good it is, and no matter how good you are, eventually it will break. "

    "Personally, I believe that if we write our CE, text books, and curricula at the physician level instead of the kindergarten level, our medics and EMTs will rise to the occasion and meet the higher standard....."



    Youtube of PPT, www.slideshare.com Post your best, share with the rest!

  8. #8
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    Quote Originally Posted by croaker260 View Post
    You completely misunderstood the thread. It wasnt "I want to give Benadryl to an asthmatic for asthma". It was " I want to give benadryl to an asthmatic who is having an allergic reaction".
    My bad. I think I've been misinterpreting some of the previous terminology. I wouldn't call bronchospasm secondary to an allergic reaction an asthma attack, per se. I've been taught that benadryl is a first line tx for a localized skin reaction. If the reaction becomes systemic(this is where the condition crosses over to anaphylaxis),the pt will still be given benadryl, but epi IM should be administered promptly. This will quickly and definitively reverse the reaction. Cardiac hx is a concern, of course, but I've seen anaphylactic reactions progress rapidly. If you wait too long, the pt will go hypotensive and shunt, and the IM epi may not circulate at that point. Just be ready to treat any untoward cardiac issues. I see no reason to give benadryl to an asthma exacerbation that was not caused by an allergic reaction.

  9. #9
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    Quote Originally Posted by mitllesmertz1 View Post
    But if an asthmatic was having a life-threatening allergic reaction, I wouldn't hesitate to give it.
    that's the way I see it too.
    I would.

    Epi, 0.3-0.5mg, SQ 1:1000 for life threatening allergic reactions and anaphylaxis.

    I would follow it up with benedryl, and solumedrol.
    AJ, MICP, FireMedic
    Member, IACOJ.
    FTM-PTB-EGH-DTRT-RFB-KTF

  10. #10
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    Quote Originally Posted by BLSboy View Post
    Epi, 0.3-0.5mg, SQ 1:1000 for life threatening allergic reactions and anaphylaxis.

    I would follow it up with benedryl, and solumedrol.
    Yep, and a good 'ol fashioned bronchodilator. It's easy to throw together a neb treatment and let the patient toke on it while you're setting up your equipment and meds. Some may say that Albuterol (or whatever your service uses) won't make it far enough to work if the airway is moderately to severely constricted, but I'm a firm believer that if the patient is moving air, a neb treatment will be worth the 15 seconds it takes to assemble.

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