Drug Math Tutorial Part II

In this part I am going to go over drug concentrations. This is a vital part of your drug calculation.

Most drugs you will encounter will be in a measure of grams.

Milligrams = mg
Micrograms = mcg (sometimes μg or ug)

1000 mcg = 1 mg
You can just move the decimal point three places to the left or right depending on what you are converting.

A whole number is a number that doesn't have a fraction or decimal following it.

4.25 is not a whole number
4 is a whole number

Whole numbers have an invisible decimal all the way to the right of the number. For example, the number 24 has a decimal after the 4, and is equal to 24.0

To convert 400 mg to mcg move the decimal to the right three places.
400 mg = 400,000 mcg

To convert 10 mcg to mg move the decimal to the left three places
10 mcg = 0.01 mg
Another unit of measure commonly used for medications is the milliequivalent.
Milliequivalent = mEq
A milliquivalent is 1000th of an equivalent. An equivalent is a form of measure used in chemistry to denote one mole of hydrogen ions in an acid-base reaction. This is the definition of the term as it is used in the prehospital setting.

The last unit of measure I am going to briefly go over is the milliliter. Milliliters are used to measure an amount of fluid. This is how we measure our normal saline and lactated ringers.
milliliter = ml
1 ml = 1 cc

When we are talking about concentrations we are talking about how much drug per amount of fluid.
25 mg / 5 ml
This denotes 25 mg of a drug in 5 ml(cc) of fluid.
When you are going to administer a medication, it is important to minimize your concentration per milliliter. This way when you can get your dose in milliliters so you know exactly how much fluid to draw up or mix into a bag.

To do this divide the left side (the mg, mcg, or mEq) by the right side (the ml or cc).
10 mg / 5 ml
10 divided by 5 = 2
2 mg / 1 ml or 2 mg/ml
25 mg / 5 ml = 5 mg / ml
1 ml is equal to "ml"
400,000 mcg / 250 ml = 1600 mcg / ml
Here is a video from MediCcast that might help:

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Practice minimizing the following concentrations to 1 ml
  1. 500 mcg / 50 ml
  2. 25 mg / 250 ml (first convert this to mcg)
  3. 10 mg / 2 ml
  4. 500 mg / 250 cc

In part III we will combine these concentrations with common medication doses.

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