Overdose, underdose, or just-right dose

October 13, 2009 9:08 AM

Hey Hive Mind - Mind Helping Me Understand Medicine Dosage?

The recommended dosage on OTC medicines has always confused me. Every medicine separates its dosages into two groups: Adults over age twelve, and kids. So how did they make that distinction, but no others? Should I be adjusting my dose based on my size?

Sometimes I will be hunkered down under a blanket with a particularly egregious headache wondering why those two aspirin I took aren't working at all, and I can't help but think it might be because the bottle recommended I take the same dose as a 75-pound preteen girl. I'm a gorilla of a man! 220 pounds! I can bench press a house! Surely I should be taking a larger dose than little Suzy Pigtails.

Same deal with vitamins and supplements - I like to take a multivitamin and fish oil capsules, but I wonder if being such a large gentleman means I should take more.

What do you think, Hive Mind?

posted by Willie0248 to health & fitness (7 comments total)

I'm roughly your size, and as a rule of thumb, i take 3 advil instead of two. Without going into dosing and toxicity, that's fine for most OTC meds, with the possible exception of tylenol or other acetaminophen-containing drugs, as that can cause liver failure.
posted by Oktober at 9:13 AM on October 13

I would be careful with vitamins, but you definitely have some leeway with simple pain relievers and cold medicine, etc. To be sure, you should simply ask your doctor. But I would venture a guess that if it says 2, you should easily be able to take 3, if not double it.

The prescription strength of ibuprophen is equal to 4 of the over the counter tablets, and that's safe for a 100 lb woman, so that should be a good example of how the medicine companies error on the side of caution (very much so) with their dosage suggestions.

IANYD, of course
posted by Eicats at 9:16 AM on October 13

Be careful with pain killers (do a bit of research on safe vs. not safe doses. Sometimes it's not the body weight you have to be careful with, it's the liver. And liver size doesn't scale with body size the same way that the effect of the pain killer might. So if you take enough painkiller to knock out your pain, you may be overdosing your liver.

Some drug's OTC doses are disturbingly close to a dangerous dose. Sometimes within 3 or 4x of the dose can be dangerous, and it's easy to sneak up on that by taking 4x Tylenol's instead of 2 over the course of a few days. Many (most?) drugs build up in your system as you keep taking them.

They were just talking about Vicodin which is 2 drugs, one opiate and acetaminophen combined into a single pill. They were looking at taking it off the market because enough people were hurting themselves by doubling up with normal OTC acetaminophen.

Anyway, long story short: you can up dosage a bit, but be careful, especially with drugs you don't know about, and even more especially, pain killers.
posted by cschneid at 9:22 AM on October 13

Does benchpressing make your liver work harder? No. That's one of the big things in oral medication - how much of it is filtered out in first-pass metabolism, that is, through your liver. Since liver function declines with age, and can be affected by alcohol intake, said weedy preteen may have a greater liver function than you do.

OTC medication is much more 'rule of thumb' than prescribed, which can be more accurately dosed to take into account things like patient size, underlying conditions, and various other things. So you might be ok upping the dosage, but I wouldn't have a go without discussing your particular circumstances with your doctor.
posted by Coobeastie at 9:25 AM on October 13

OTC meds are generally effective over a wide range of dosages and the difference between what is effective and what is toxic (therapeutic index) is very large. The recommended dosages are at the lower end of the range to minimize the risk of overdosage but should still be effective even for much larger people. There are a lot of factors that enter into how an effective dose of a drug varies with body weight and it is the subject of much medical literature. Things like protein binding, lipid solubility, rate of absorption from the GI tract, first-pass metabolism, the presence or absence of active metabolites, the rate of metabolism and elimination, and so on make each drug different in this regard, but in general, a drug whose effectiveness varies widely with the size of the patient is not likely to be approved for OTC use.

The FDA mandates how the labels read; some medicines include adults, children under 12, and children under 6, and pediatric medicines have their own age groups. For an idea of how detailed the regulation regarding drug labels are, take a look here.
posted by TedW at 9:41 AM on October 13

You should ask your pharmacist whether taking a larger dose would be appropriate.
posted by grouse at 10:16 AM on October 13

You should ask your pharmacist whether taking a larger dose would be appropriate.

Seconding this. Your pharmacist should be able to tell you the maximum safe dose to take at one time, and the total safe amount to take in a 24 hour period. Especially with painkillers, there is a limit to how much one should take in a day because of the damage it can do to your liver and potential lethal side-effects.
posted by geeky at 10:57 AM on October 13