copyright © 2008 thomson delmar learning conversions: between and within systems revised...

Copyright © 2008 Thomson Delmar Learning

Conversions: Between and Within Systems

Revised KBurger0808

Textbook Assignment:

Pickar, G. (2007). Dosage calculations: A ratio-proportion approach. (2nd ed.)Chapter 4


Equivalents1 grain (gr) = 60 milligrams (mg)1 teaspoon (t) = 5 milliliters (mL)

1 tablespoon (T) = 3 teaspoons (t)1 ounce (oz) = 30 milliliters (mL)

1 cup = 8 ounces (oz)1 Kilogram (Kg) = 2.2 pounds (lbs)

1 liter (L) = 1000 milliliters (mL)1 gram (g) = 1000 milligrams (mg)

1 milligram (mg) = 1000 micrograms (mcg)

The equivalents listed in blue are only considered approximate equivalents


Converting Using Ratio-Proportion

• Rule– Recall equivalents– Set up a proportion of two equivalent ratios– Cross-multiply to solve for an unknown quantity, X



• Remember– Each ratio in a proportion must have the same

relationship and follow the same sequence– A proportion compares like things to like things



• Remember– The units of measurement in both numerators and

denominators must match– ALWAYS, ALWAYS, ALWAYS label the

measurement units in each ratio INCLUDING your unknown quantity X



• Example– How many feet are in 36 inches?


1 foot = 12 inches

1 ft

12 inX ft

36 in

12X 36

12X

12

36

12

X 3 feet

Converting Using Ratio-Proportion• Recall equivalent

• Set up a proportion of two equivalent ratios

• Cross multiply to solve for “X”

• Label units to match the unknown “X”


1 gm=1,000 mg

1 gm

1,000 mg

5g

X mg

X 1,000 5

X 5,000 mg

Using Ratio Proportion to Convert Within Metric System

• Recall equivalent

• Set up a proportion of two equivalent ratios

• Cross multiply to solve for “X”

• Label units to match unknown “X”

EXAMPLE: Convert 5 grams to milligrams


Converting Within the Metric System

Short Cut• Medication conversions within the metric system

most often occur between: mg and mcg [ mg are larger than mcg ] g and mg [ g are larger than mg ] L and mL [ L are larger than mL]

• These are all 3 decimal place differences[ a difference of 1000 ]

• To use this Short Cut you will need to remember-which unit is larger-to always move 3 decimal places


Conversion Slide• Keep this visual in mind when

converting within the metric system

kg g mg mcg

Move decimal point three places between each unit


Converting Within Metric SystemShort Cut continued

• Write out the desired equivalent in this format 5 mg = ______ mcg

• Then draw an arrow that starts at the larger unit and points toward the smaller unit Larger to Smaller

• Move the decimal point in the direction of the arrow by three places.


Calculating a Drug Dosage that requires Conversion between Systems

• Drug order reads Codeine sulfate gr ¾ p.o. q.4h p.r.n., pain

• Drug supplied is Codeine sulfate 30 mg per tablet• Calculate one dose


Converting to Same System

• Drug order reads Codeine sulfate gr ¾ p.o. q.4h p.r.n., pain

• Drug supplied is Codeine sulfate 30 mg per tablet

• What do you notice?– Different system– Needs to be converted


Approximate Equivalent: gr i = 60 mg

• Step 1. Convert – Convert to equivalent units in the same system

of measurement. Convert gr to mg. – Approximate equivalent: gr i = 60 mg.


Convert usingRatio Proportion Method

• Start by writing a known ratio: 1 grain = 60 mg [ the known equivalent ]

• Then fill in the rest of the proportion• Solve for X

1 gr ¾ gr 60 mg = X mg

1X = 60 x ¾ (0.75)X = 45 mg

• Codeine gr ¾ = 45 mg


Think

• Step 2Stop and think carefully about what a reasonable dosage should be:You have just figured out that the doctor ordered 45 mg. The drug label indicates that each tablet = 30 mg.Will you be giving more or less than 1 tablet?

MORE


Step 3: Calculate usingRatio Proportion Method

• Start by writing known ratio from the problem• Complete the proportion with other information you have

[doctor’s order ]• Check for matching units.

Cross multiply and solve for X• 30mg 45mg 30X = 45 1 tablet = X tablet X = 45 = 1 15 = 1 ½ tablets

30 30

copyright © 2008 thomson delmar learning conversions: between and within systems revised...

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