This seems to be a US (UK?) thing? At least here in the German speaking countries in Europe aspirin also has nice round numbers. A dosage for heart attack prevention is usually 100mg. Normal dose is 500mg
As you can see on the NHS (UK National Health Service) website[1]:
The usual dose to prevent a heart attack or stroke is 75mg once a day (a regular strength tablet for pain relief is 300mg).
The usual dose for pregnant women is either 75mg or 150mg, taken once a day.
The daily dose may be higher, up to 300mg once a day, especially if you have just had a stroke, heart attack or heart bypass surgery.
Also says similar in the BNF (British National Formulary)[2]
It seems like you'd want to base your choice on two main criteria:
1. The lowest effective dosage.
2. The dosage with maximum efficacy vis-a-vis what is studied in the literature.
At a cursory glance, it seems like many studies compare a lower dosage of aspirin to a higher dosage (e.g. 75mg to 300+mg) and the lower dose tends to compare favorably.
Having nice round numbers is of no benefit to a patient.
> Having nice round numbers is of no benefit to a patient.
At our current level of logistical sophistication, the benefit-to-the-patient is that they can get their medications at all.
I agree that in a perfect world every prescription would start with a computation, based on body weight and historical susceptibility and suchlike, to determine precisely the right dosage. However, I also don't think we're there yet. I don't think that you can reasonably prescribe "take 6 milliliters of this" or "take thirteen of these"; patients would mess that up reliably even if they were in perfect health and had perfect vision and perfectly stable hands. And we can't stock thirty different sizes of pill; each size of pill takes up already-limited shelf space, increases cost of packaging and logistics, and increases the likelihood of dosing error. So doctors can't yet prescribe precisely the dosage they should be able to. I'm sure that there are cases where they do - drugs with narrow therapeutic ranges administered in hospital settings where they can be precisely dispensed by IV - but for stuff that's being sent home with patients, we're just not there yet.
(Sadly, even on-demand services like pillpack won't save us, because doctors can't depend on the availability of custom pill-stamping when they make a prescription - they have to assume that the lowest-common-denominator pharmacy is being used to fill the prescription.)
(In fact, going by the rate at which hospital mortality is attributed to dosing errors during administration, we haven't solved precision pharmacology even under ideal circumstances and fundamental breakthroughs are required that will obsolete any current approach to dispensation of prescription medication.)
It’s all “round numbers”. 81mg is just 1.25 grains, a quarter of the normal 325mg dose which is just 5 grains. It’s not like
anyone did a clinical study to determine the effective dosage to two significant figures.
Has been working ok for hundreds of millions, so there's that.
Almost all drugs are sold in "nice round numbers" anyway.
Given that you can drop orders of magnitude in scale from grams to milligrams (or whatever) to suite the dosage calculation, nobody is going to notice the difference between X with decimal points and Y which is X rounded, as if 247.3mg was going to be optimal and 250 will be bad.
The variability of what the patient actually needs (e.g. an adult male could be 1.55 and 50kg to 2.10 and 150kg but they usually just get the same dosage in the instructions - and for most drugs no doctor would bother to suggest a more fitting value) would be higher than any rounding error anyway, but in practice it hardly matters.
> Having nice round numbers is of no benefit to a patient.
Patients benefit from simplicity just like practitioners, they have to do math like whether they've reached 1500mg in a day or need to split pills when there is an availability problem (for a dosage.)
An optimal dose to be served to everyone is also a myth as dosing is calculated by weight, etc.
In Ireland, I'm sure I've seen 325mg doses of aspirin and been puzzled by it. I assumed it was just a little bit stronger than paracetamol. While that's probably true, I can see now it's a bit arbitrary too.
Though maybe I'm misremembering or thinking of aspirin someone brought from the US. When I look up one of the most common asiprin brands here, it seems it is 300mg, not 325.
What ends up happening is a big study is done on an existing formulation of an old drug, results look good, and then you have to ask yourself: do you mess around with the dosing to get a round number, or go with what's been proven?
Nope. Just a US thing.
As you can see on the NHS (UK National Health Service) website[1]:
Also says similar in the BNF (British National Formulary)[2][1]https://www.nhs.uk/medicines/low-dose-aspirin/how-and-when-t... [2]https://bnf.nice.org.uk/drugs/aspirin/