The flash player was unable to start. If you have a flash blocker then try unblocking the flash content - it should be visible below.
Not all hives mean allergy!
Thank you for the comment. I think a bunch of things were combined here, making it unclear. Urticaria right after starting amoxicillin might be an allergy to amox, but urticaria several days after starting amox is likely due to the underlying infection NOT an amox allergy. Amox can also cause a rash that is not an allergic reaction, as can the underlying infection- anyone's guess as to what that is due to if it starts a few days into the treatment course, but it is unlikely to represent an allergy either way. Too many recaps- I guess this is what comes of Rob having to have the last word!!!
The discussion here on sedating vs. non-sedating antihistamines raises a few questions particularly important to me. I'll list the questions again at the end so that anyone responding doesn't have to dig them out of my discussion. As background, I'm an RN and EMT but also a professionally trained search and rescue volunteer. We get somewhere between 30-35 call outs per year so we're also rather busy. I drafted our team's medical protocols with one of the ED physicians I work with as our medical director. Our current treatment for allergic reaction/anaphylaxis for adults is as follows:
-0.3-0.5 mg epi 1:1,000 IM anterolateral thigh for anaphylaxis-50 mg diphenhydramine PO-150 mg ranitidine PO
Anyone requiring epi will buy themselves transport to the nearest ED. In my ED we generally use famotidine IV as our H2 blocker when we have a reason to obtain IV access. Assuming PO route only, my H2 blocker of choice is currently ranitidine. I've made this decision in using surrogate markers of time of onset to reduced gastric acid secretion comparing raniditine to famotidine. It seems ranitidine has an onset of action of approximately 55 minutes versus 90 for famotidine. Again, this is a surrogate marker, but I'm unaware of comparisons between the two for allergic reaction. Clinically significant? I don't know, but they're both cheap and I see no harm in using ranitidine over famotidine. Would there be a reason to use cimitedine or another H2 blocker instead? I know there's not great evidence that H2 blockers even make much of a difference here so devoting too much thought to choice of agent may be a waste of time. If using ranitidine would you suggest 150 mg or is there benefit (or harm) to giving 300 mg as the initial dose for this use?
Is there any reason I shouldn't be treating acutely with an antihistamine other than diphenhydramine? My take away from this portion of the podcast was that it focused a bit more on subacute care at home, so I just want to clarify with that question. I'd like to avoid sedating antihistamines so people can still safely drive home from a search or continue to participate in search operations when appropriate. Diphenhydramine and loratidine both have similar onset times (approximately one hour) when given PO while loratidine is non-sedating and requires less frequent redosing so I'd rather use loratidine if it's appropriate in the acute treatment. If using loratidine (for adults) is the preferred dose 10, 20 or 40 mg for acute treatment? Loratidine is available in an oral solutab (diphenhydramine has a version as well). Is there clinical significant benefit to using the solutab over tablet form?
Again, my questions are:
1. Is there a preferred PO H2 blocker?2. If using ranitidine for acute care of allergic reaction is there a reason to use 300 mg or is 150 mg (or even 75 mg) adequate?3. Can loratidine or another non-sedating antihistamine replace diphenhydramine in the acute care of allergic reaction?4. If using loratidine in the acute care of allergic reaction is the appropriate dose in adults 10, 20 or even 40 mg?5. Should I use the solutab form of my administered antihistamine or is standard tablet likely just as good?
Any expertise is much appreciated.
Response from Dr. Kelso:1. Is there a preferred PO H2 blocker?2. If using ranitidine for acute care of allergic reaction is there a reason to use 300 mg or is 150 mg (or even 75 mg) adequate?
As you state, there is really no data to say that adding an H2 blocker is helpful in anaphylaxis, but the consensus is that it would likely not hurt. Ranitidine has been used in this circumstance.According to UpToDate https://www.uptodate.com/contents/anaphylaxis-emergency-treatment?source=machineLearning&search=h2%20antihistamines%20anaphylaxis&selectedTitle=1~150§ionRank=1&anchor=H30#H30"H2 antihistamines - An H2 antihistamine given with an H1 antihistamine may provide some additional relief of hives.
Although H2 antihistamines are sometimes administered in anaphylaxis treatment, H2 antihistamines DO NOT relieve upper or lower airway obstruction or shock. Systematic reviews have not identified any randomized, controlled trials that support the use of these agents in anaphylaxis or urticaria.
If used, ranitidine (50 mg in adults) (12.5 to 50 mg [1 mg/kg] in children), may be diluted in 5% dextrose to a total volume of 20 mL and injected intravenously over five minutes."
Nurmatov UB, Rhatigan E, Simons FE, Sheikh A. H2-antihistamines for the treatment of anaphylaxis with and without shock: a systematic review. Ann Allergy Asthma Immunol 2014; 112:126.3. Can loratadine or another non-sedating antihistamine replace diphenhydramine in the acute care of allergic reaction?4. If using loratadine in the acute care of allergic reaction is the appropriate dose in adults 10, 20 or even 40 mg?
Cetirizine is the most widely recommended less or non-sedating antihistamine to be used in this circumstance.
"For oral treatment, second-generation H1 antihistamines (eg, cetirizine) offer certain advantages over first-generation agents (eg, diphenhydramine, chlorpheniramine, hydroxyzine, and promethazine). Second-generation H1 antihistamines are less likely to impair cognition or psychomotor performance (eg, the ability to drive safely) or to cause sedation.
Orally-administered cetirizine acts within 30 to 40 minutes and lasts for 24 hours. However, second-generation H1 antihistamines are not available in parenteral formulations."
5. Should I use the solutab form of my administered antihistamine or is standard tablet likely just as good?I am not aware of any data regarding the onset of action of the soluble tablets or syrup versus standard tablets, but the fact that the soluble tablets do not require the availability of water to swallow may be an advantage.
John Kelso M.D.
Thank you for the prompt and detailed response! I believe I'll be switching to certirizine as my H1 blocker of choice for my search and rescue gear.
What you do matters.