The lady in the cube next door to mine says she has a screaming headache. I produce a bottle of Motrin from my desk and offer it to her. She gladly accepts and all is well in the office.
But I can’t help but wonder at the fact that I’m 250 lbs plus and she’s 110 lbs soaking wet with rocks in her pockets. Yet the OTC pain reliever makes no allowances for my body mass being better than twice hers. Medicine for very young children ups the dosage to account for weight increases as the child grows. Even the medicines I buy from the vet for the dogs fall into fairly narrow weight ranges (0-10lbs, 10-20 lbs).
Why doesn’t OTC medicine for people have some similar dosing scheme?
-rainy
[edited beacause I’ve never used the edit button before ]
WAG here, but I’d imagine it has to do with the fact that OTC medications are OTC because they have a very low toxicity, even across a large range of dosages. So, they shoot for the maximum labeled dosage that will be effective for nearly everyone. The 97-pounders get a pretty large relative dose, but minimal side effects because of the low toxicity.
Most likely it’s to make it easy to follow the instructions, “take 2 tablets every 4 hours” is easier to understand than “take 1 tablet per 50kg every 4 hours” or “take 2mg per kg”. The dose described on the bottle/package will be one worked out to be effective for the widest range of people. However, that does mean that some people will fall outside that range and potentially will not get a therapeutic dose.
Because the general public would screw it up and end up taking 10x doses or .1x doses or anything in between or just plain not be able to figure it out. I mean telling someone how much medicine to take in mg/kg or mg/lb is going to be hard for a lot of people to get. And even if they can figure out how many mg to take, then they have to figure out how many pills that is which could easily wind up going the wrong way and multiplying instead of dividing. And then what if they firgure out that it should be 750mg but the pills are 500mg each, then what. And heaven forbid a decimal gets out of place during the calculations. …Slow down Joey, take a breath… So they just factor in a huge margin of safety. If two pills don’t work, you get two take two more in a few hours and maybe by then it’ll work. If you tell your doctor that two don’t work, then the doctor can decide how many you should take. I beleive the doctors orders trump the directions on the back of the bottle.
And to add to that, even if people got used to that, then something would come along that would require large enough doses to speak in terms of grams or small enough that it uses micrograms and doses would get screwed up again.
Also, I’ve noticed that most OTC meds are designed so it’s two pills every X hours. The other thing about figuring out your own dose is that some things will be two pills, some one pill, some four pills and that would be really confusing.
Well sure, but they *could *make it a range, like children’s medicine does now.
Weight…Dose
50-100lbs…1 tablet every 4 hours
100-150lbs…2 tablets every 4 hours
150-200lbs…3 tablets every 4 hours
Over 200lbs…consult your physician
I think the (cynical) answer is that for most things it just doesn’t matter much because the stuff is crap anyway. Certainly most cold medicines work mostly on prayer and placebo, since they’ve taken the good stuff off the market.
For things like Tylenol, they’re not interested in providing you with an effective dose, but in preventing overdose and lawsuits. If they can show the court that you didn’t follow the label directions, then your pickled liver is not their problem.
Finally, not everything is dosed by body weight. Some things are dependent on liver metabolism or other factors that don’t vary by weight.
I weigh around 300 lbs. but, I tend to be fairly sensitive to medication. I only take half an actifed and find it is quite effective and a whole one will bring on nosebleeds without helping more. Even for migraines and don’t need more than the basic dose of ibuprophen unless I have extraordinary pain like after surgery.
There is more than weight that factors into dosage. If the exact dosage is that sensitive, it wouldn’t be OTC.
People vary genetically in terms of various enzymes that break down most drugs (the CYP 450 set of enzymes in the liver and elsewhere.) They also can produce more or less of those enzymes depending on what they’ve been exposed to recently. Think about how someone can build up a tolerance to alcohol if they drink it often- their livers are making more of the relevant enzyme because they’re frequently trying to break down that particular toxin. The same enzyme that breaks down alcohol also breaks down various medications, and someone with a high tolerance to alcohol will need a bigger dose of those drugs than would someone with a low tolerance, because the enzymes will clear it out of their system faster. All of this is a roundabout way of explaining that it’s not just weight that does it, although I agree that if they can change the dosing of acetomenophen for kids based on age, which is a proxy for weight (age 2-3, take one chewable, 4-6, 2 chewables, etc.) they can do it for adults, too.
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