I had a moderate allergic reaction to peanuts last night. I took diphenhydramine (Benadryl) and the hives had subsided by this morning. Lecturing on perturbation theory was more challenging. I felt like I was walking in a fog. Which got me to wondering, just what was the half-life of Benadryl? Benadryl has a relatively long half-life, between 8 and 10 hours. A typical 50 mg dose leads to a peak blood level of around 80 nanograms/ml. Most people feel drowsy at blood levels around 30 nanograms/ml. Assuming first order kinetics apply to the breakdown/elimination of Benadryl, a 30 nanogram/ml is not unlikely 10 to 15 hours later. Which would certainly explain my fogged state this morning! But not so foggy as to be unable to work the kinetics....
Monday, November 13, 2006
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3 comments:
Interesting. This explains why summer passed me by in a haze of diphenhydramine!
For some reason I thought the half life was relatively rapid and I was just responding strangely.
I had to stop taking benadryl for allergies unless I was planning on staying home for a day -- it just makes it too hard to work!
I'm one of the lucky people who do not get sleepy from antihistamines. Any idea why it doesn't affect me? I guess the real question should be why does it put you in a fog?
By the way, the abbreviation for liter is upper case, i.e. L. Thus the abbreviation for milliliter is mL not ml. This became official back in the 1970s and published in the Federal Register which has the final say since liter is a uniquely American unit.
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