Neurotic question about NSAIDs, covid vaccine

February 17, 2021 5:39 PM

Nothing I can do about it now, but the basic question is: how long is tylenol in your system to an extent that it might interfere with the 2nd dose of the Moderna vaccine. YANMD but maybe you have reassuring words.

I had a nagging headache last night. I knew you weren't supposed to take NSAIDs right before the covid vaccination but it was 12+ hours away and I figured you're supposed to take tylenol/advil about every four hours when you're sick, so it must not linger in your system. Got shot #2 this morning, now slightly concerned I could have diminished the efficacy. Should have asked before rather than after but it was the kind of headache where you're not thinking super clearly.

Have I fucked up?

posted by less of course to Health & Fitness (7 answers total)

Acetaminophen (Tylenol) is not classified as an NSAID.
Ibuprofen (Advil) is.
Which did you take?
posted by Thorzdad at 5:42 PM on February 17, 2021 [3 favorites]

Response by poster: Ok, my bad, I thought it was a category that covered Advil and Tylenol. I am aware you're not supposed to take either before the vaccine. Mutatis mutandis, my question remains. I took acetaminophen.
posted by less of course at 5:45 PM on February 17, 2021

Best answer: I suspect 12+ hours is more than fine, and you haven't diminished anything. I am not a pharmacist, but Dr. Wikipedia gives the elimination half-life of paracetamol/acetaminophen as 2–2.5 hours. If you halve the amount of acetaminophen in your body every 2 hours, after 12 hours, there's less than half of 1% of the original dose left.
posted by zamboni at 6:18 PM on February 17, 2021 [1 favorite]

Best answer: I was very confused about this question, googled it, and found that a bunch of news sites are reporting this as some kind of hot story but citing CDC Guidelines that only makes this suggestion as part of patient counsel instructions:

"Antipyretic or analgesic medications (e.g., acetaminophen, non-steroidal anti-inflammatory drugs) can be taken for the treatment of post-vaccination local or systemic symptoms, if medically appropriate. However, routine prophylactic administration of these medications for the purpose of preventing post-vaccination symptoms is not currently recommended, because information on the impact of such use on mRNA COVID-19 vaccine-induced antibody responses is not available at this time.

In addition, administration of antihistamines to COVID-19 vaccine recipients prior to vaccination to prevent allergic reactions is not recommended. Antihistamines do not prevent anaphylaxis, and their use might mask cutaneous symptoms, which could lead to a delay in the diagnosis and management of anaphylaxis."

but having done so is not an actual contraindication in the next section of the document - as in there is no guidance to administrators to cancel administering the vaccine if the patient has done these things.

Bottom line: they don't know either way if it's a problem because they didn't test for it, but they do know that lots of people do exactly this before getting shots and are saying there is no advice to do so in this case. But millions of people take these medications on a regular basis, and they go on to say you are free to use it immediately after injection, and this is not a magic vaccine - it takes time to work. If having taken some Tylenol at some point beforehand was going to cancel the vaccine, taking it afterwards would too. They would screen for it and have you come back another day.
posted by Lyn Never at 6:25 PM on February 17, 2021 [9 favorites]

Hard to see how you would hit the 94% efficacy rate in the general population if something like a tylenol in the previous 24 hours was powerful enough to significantly disrupt the vaccine.
posted by jenkinsEar at 6:32 PM on February 17, 2021 [4 favorites]

Even if it did, both of the two dose vaccines seem to have pretty good efficacy even after a single dose. There have been arguments about postponing the second dose in order to get more first doses into people. Same thing, it's not been trialed in that way. To some extent, if such drugs could impede the immune response to the actual virus, we wouldn't need the vaccines. The probably just don't want you to mask symptoms of infection (fever, etc.) or symptoms of a bad reaction during the fifteen minutes or so that they want you to wait to make sure you don't have an adverse reaction.
posted by zengargoyle at 6:40 PM on February 17, 2021

You can get an answer for most any medication by searching on "half life x" as in "half life Advil".
posted by SemiSalt at 4:38 AM on February 18, 2021