From:
Claire Curtis
Date: 2001-10-21 11:49:00 UTC
Subject: Metric system (was Melatonin dosage)
Hi Donna et al --
Confusion with our meds is pretty common, since most Americans don't use
the metric system much.
The metric system was designed to be a system that would all fit
together logically. And it really does make sense. It was originally
based on the size of the Earth and on the properties of water.
A meter was calculated to be one-millionth of the distance from the pole
to the equator. It's a bit more than a yard; think of a it as a yard of
cloth from a shop that gives you extra for mistakes. A centimeter (cm)
is one-hundredth of a meter, just as a cent (centi-dollar) is
one-hundredth of a dollar.
A cubic centimeter (cc) is a box 1 cm along each side. That makes it
about the volume of the end of your little finger.
Fill that box with water at room temperature, and it weighs one gram.
Take 1000 of those grams of water, and you have a useful size liquid
volume, a liter. It's about the size of an American quart. So that
little box of water can also be described as being one-thousandth of a
liter, or a milliliter.
So yes, 1 ml = 1cc. One is based on the length measurement and one is
liquid volume, but in practice the two terms are interchangeable.
For a medication, you want to know how much medicine is dissolved in the
liquid. The medicine is usually measured by weight, so you have
milligrams (mg) or even micrograms (ug) (that u is actually the greek
letter 'mu', but when typing it a u is substituted) per milliliter of
liquid.
If a medicine is 10 mg/ml, and you only want to give 5 mg of medicine,
then you give half the amount -- ie, half a ml.
Hope this helps.
-Claire
PS- I taught medical assisting for some years, and came to the
conclusion that a good part of the problem is that our schools 'teach'
the metric system by having students convert measurements. They try to
memorize conversion factors, get confused about what gets divided by
what, and give up. I found that the thing that most helped students
'get' the metric system was the image of 1 ml being the size of the tip
of their little finger.