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Why is the penicillin/ceftriaxone hypersensitivity test only done once?
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Posted by
Mina Laban
Why is the penicillin/ceftriaxone hypersensitivity test only done once?
There already has been an answer but I'd still like to clarify further. I'm assuming the OP was expecting a second skin test because type 1 hypersensitivity requires a repeat exposure. Getting exposed to the antigen will just get you sensitized but will not precipitate the reaction.
What I want to clarify is that the skin test doesn't test whether you are allergic to a medication but if you are already sensitized to it. It is important to get the difference.
If you have. never been exposed (hence sensitized) to ceftriaxone before, the test would be negative even if you are actually allergic. And as sensitization needs time, you wouldn't be getting tested right afterwards (as mentioned in the comments). Instead, you'll be given the dose.
So why skin tests? That's because the dose is low and intradermal - chances of a full blown anaphylaxis are lower (not zero) even if the pt. is previously sensitized.
So, to conclude, as mentioned in the previous answer, the skin test is done just once to check if you've already sensitized, since rarely do people precisely remember the medications they have been previously exposed to.
There already has been an answer but I'd still like to clarify further. I'm assuming the OP was expecting a second skin test because type 1 hypersensitivity requires a repeat exposure. Getting exposed to the antigen will just get you sensitized but will not precipitate the reaction.
What I want to clarify is that the skin test doesn't test whether you are allergic to a medication but if you are already sensitized to it. It is important to get the difference.
If you have. never been exposed (hence sensitized) to ceftriaxone before, the test would be negative even if you are actually allergic. And as sensitization needs time, you wouldn't be getting tested right afterwards (as mentioned in the comments). Instead, you'll be given the dose.
So why skin tests? That's because the dose is low and intradermal - chances of a full blown anaphylaxis are lower (not zero) even if the pt. is previously sensitized.
So, to conclude, as mentioned in the previous answer, the skin test is done just once to check if you've already sensitized, since rarely do people precisely remember the medications they have been previously exposed to.
Because developing a hypersensitivity takes time. If you get exposed to an allergen, the body first has to produce those antibodies that then get used in the hypersensitivity response at the second, or subsequent, exposure.
If you are talking about taking a second test just minutes after the first one, how would your body even "know" that this is a second exposure? Two exposures within minutes are not distinguishable from one exposure for the body.
Usually, an allergic reaction shows the second time a patient takes a full course of antibiotics. It does not show at the second oral dose or injection, which are way too close to the first dose to have already lead to the developing of a hypersensitivity.
So, why test you in the first place? Because you might have been exposed previously without remembering it - people misremember what medication they got during their childhood all the time, I imagine, and your doctor/nurse seem to just routinely do the test before giving these antibiotics.
Because developing a hypersensitivity takes time. If you get exposed to an allergen, the body first has to produce those antibodies that then get used in the hypersensitivity response at the second, or subsequent, exposure.
If you are talking about taking a second test just minutes after the first one, how would your body even "know" that this is a second exposure? Two exposures within minutes are not distinguishable from one exposure for the body.
Usually, an allergic reaction shows the second time a patient takes a full course of antibiotics. It does not show at the second oral dose or injection, which are way too close to the first dose to have already lead to the developing of a hypersensitivity.
So, why test you in the first place? Because you might have been exposed previously without remembering it - people misremember what medication they got during their childhood all the time, I imagine, and your doctor/nurse seem to just routinely do the test before giving these antibiotics.
I'm not sure of something you assume in your answer (because the question is unclear): I don't think the OP is talking about the second dose (though he might be), but rather the second course of antibiotics (at least, I hope that's what was meant.) Also, you might want to read about amoxicillin-associated rashes.More
@anongoodnurse I thought he was talking about the course of antibiotics being the second exposure, the first being the skin test. But it's unclear. What do you mean with those rashes? Or rather, what do you mean with them in relation to this question/answer?More
There already has been an answer but I'd still like to clarify further. I'm assuming the OP was expecting a second skin test because type 1 hypersensitivity requires a repeat exposure. Getting exposed to the antigen will just get you sensitized but will not precipitate the reaction.
What I want to clarify is that the skin test doesn't test whether you are allergic to a medication but if you are already sensitized to it. It is important to get the difference.
If you have. never been exposed (hence sensitized) to ceftriaxone before, the test would be negative even if you are actually allergic. And as sensitization needs time, you wouldn't be getting tested right afterwards (as mentioned in the comments). Instead, you'll be given the dose.
So why skin tests? That's because the dose is low and intradermal - chances of a full blown anaphylaxis are lower (not zero) even if the pt. is previously sensitized.
So, to conclude, as mentioned in the previous answer, the skin test is done just once to check if you've already sensitized, since rarely do people precisely remember the medications they have been previously exposed to.
There already has been an answer but I'd still like to clarify further. I'm assuming the OP was expecting a second skin test because type 1 hypersensitivity requires a repeat exposure. Getting exposed to the antigen will just get you sensitized but will not precipitate the reaction.
What I want to clarify is that the skin test doesn't test whether you are allergic to a medication but if you are already sensitized to it. It is important to get the difference.
If you have. never been exposed (hence sensitized) to ceftriaxone before, the test would be negative even if you are actually allergic. And as sensitization needs time, you wouldn't be getting tested right afterwards (as mentioned in the comments). Instead, you'll be given the dose.
So why skin tests? That's because the dose is low and intradermal - chances of a full blown anaphylaxis are lower (not zero) even if the pt. is previously sensitized.
So, to conclude, as mentioned in the previous answer, the skin test is done just once to check if you've already sensitized, since rarely do people precisely remember the medications they have been previously exposed to.
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VOTE
Because developing a hypersensitivity takes time. If you get exposed to an allergen, the body first has to produce those antibodies that then get used in the hypersensitivity response at the second, or subsequent, exposure.
If you are talking about taking a second test just minutes after the first one, how would your body even "know" that this is a second exposure? Two exposures within minutes are not distinguishable from one exposure for the body.
Usually, an allergic reaction shows the second time a patient takes a full course of antibiotics. It does not show at the second oral dose or injection, which are way too close to the first dose to have already lead to the developing of a hypersensitivity.
So, why test you in the first place? Because you might have been exposed previously without remembering it - people misremember what medication they got during their childhood all the time, I imagine, and your doctor/nurse seem to just routinely do the test before giving these antibiotics.
Sources/Reading
Drug allergies
Update on the Management of Antibiotic Allergy
Because developing a hypersensitivity takes time. If you get exposed to an allergen, the body first has to produce those antibodies that then get used in the hypersensitivity response at the second, or subsequent, exposure.
If you are talking about taking a second test just minutes after the first one, how would your body even "know" that this is a second exposure? Two exposures within minutes are not distinguishable from one exposure for the body.
Usually, an allergic reaction shows the second time a patient takes a full course of antibiotics. It does not show at the second oral dose or injection, which are way too close to the first dose to have already lead to the developing of a hypersensitivity.
So, why test you in the first place? Because you might have been exposed previously without remembering it - people misremember what medication they got during their childhood all the time, I imagine, and your doctor/nurse seem to just routinely do the test before giving these antibiotics.
Sources/Reading
Drug allergies
Update on the Management of Antibiotic Allergy
More
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