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.

ex.

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.

• Part 1
• Part 2
• Part 3
• Part 4
• Answer Key