Take 162 mg of aspirin and call me in the morning
April 14, 2010 6:17 PM   Subscribe

I understand that doctors recommend a prophylactic dose of 81 mg of aspirin daily for alot of adults because 81 mg is the amount in a baby aspirin. But WHY is that the amount in baby aspirin? Why not 80mg, or 85mg? That one milligram can't be too crucial. Can it?
posted by mmf to Health & Fitness (11 answers total) 3 users marked this as a favorite
Best answer: The "standard" aspirin pill is 325 mg; 81.25 is one-fourth of this, and I suspect they rounded this to the nearest milligram.
posted by madcaptenor at 6:22 PM on April 14, 2010 [1 favorite]

Best answer: Aspirin doses were traditionally measured out in grains. The standard adult dose is 5 grains. 81mg is 1.25 grains.
posted by zsazsa at 6:28 PM on April 14, 2010

Best answer: For followup, why 325 mg? That used to be ' 5 grains' in the old apothecary system. It's a quarter of the standard 'full' dose.

On preview: Beaten! More on grains, then.
posted by Weighted Companion Cube at 6:30 PM on April 14, 2010

Why NOT 81mg? If that's the 'correct' dosage, why would they round it to 80 or 85 just for the sake of a clean number?
posted by csimpkins at 6:33 PM on April 14, 2010

Best answer: Why NOT 81mg? If that's the 'correct' dosage, why would they round it to 80 or 85 just for the sake of a clean number?

The difference between 80 and 81 mg is negligible and is much smaller than the allowable error in manufacturing or the different weights at the upper and lower weights for a given dose. In fact, children's acetaminophen is dosed in multiples of 80 mg, and ibuprofen in multiples of 50 mg, so some drugs dosages are rounded off to even numbers. it is noteworthy that aspirin predates the other two drugs and the standard doses were determined before the metric systems was widely used and apothecary units were the common way to prescribe drugs.
posted by TedW at 6:50 PM on April 14, 2010

Best answer: Asprin only gets scary in high does.an 81mg dose is close enough and already exists in a form people can pick up without having to create a new product.
posted by The Whelk at 7:00 PM on April 14, 2010

Response by poster: Fast, accurate and sensible.
You guys are the best. Thanks!
posted by mmf at 7:29 PM on April 14, 2010

As I recall, the aspirin-helps-your-heart trials were run with the little (81mg) tablets and showed a verifiable positive effect. This so dazzled the drug companies that they never repeated the (admittedly, expensive, time-consuming, and, worst of all, possibly nil-or-negative outcome) trials with any other dose. 81mg is a PROVEN treatment.

Would 60mg work just as well? Would 116mg work better? Or worse? Should you adjust the dose based on your weight? Your age? Your sex? Your astrological sign?

We will never know, because investigating any of these (mostly reasonably) things will never be done. We have the good news--81mg works. Better news wouldn't help anyone except the people swallowing those pills, and worse news--well, who wants worse news?

For drug manufacturers, aspirin is cheap and effective, and that's a heavy enough cross to bear.
posted by hexatron at 9:21 PM on April 14, 2010

hexatron, WebMD says:
Recent research indicates an appropriate dose of aspirin is between 80 and 160 mg per day. This is actually half of the standard 325-milligram aspirin commonly prescribed. Many studies show the lower dose works just as well as the higher dose, while reducing the risk of internal bleeding.

This would indicate that there have indeed been studies of the dosage level. (I'm not going on PubMed to find them, though.)

Incidentally, it appears that the non-US standard may be 75mg, without the avoirdupois measurements in the way.
posted by dhartung at 9:58 PM on April 14, 2010

And of course, you're not supposed to give baby aspirin to babies. :)

I believe with children under 12 you're to check with a doctor these days before giving aspirin. (They'll give you Tylenol upon birth, and ibuprofin starting officially at 6 months (but unofficially many parents give it for teething starting at 4 or 5 months; it's hard on infant stomachs so isn't official until 6 months).)

I know they call it "baby aspirin" for ease of recognition/labeling, but probably they should change it to "low dose aspirin" or "heart-smart aspirin" or something like that, since giving baby aspirin to babies is verboten!
posted by Eyebrows McGee at 7:23 AM on April 15, 2010

I know they call it "baby aspirin" for ease of recognition/labeling, but probably they should change it to "low dose aspirin" or "heart-smart aspirin" or something like that

Actually, that is what they have done. No US aspirin is labeled "baby aspirin"; the term is just a holdover from the days when we dialed phones and rolled up car windows. The reason for this is that aspirin and other salicylates are linked to Reye's syndrome, a rare but potentially fatal condition causing liver failure and brain damage. Although there are instances where the benefits of giving aspirin to children outweigh the risks; typically children with congenital heart disease who depend on some sort of artificial shunt to live. In these kids the antiplatelet effect of aspirin will prevent blood clots from forming in the artificial shunt, which could quickly be fatal.

And don't get me started on the link between aspirin and heroin.
posted by TedW at 6:13 PM on April 15, 2010

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