DRUG CALCULATIONS
MAKING IT EASY

CLASS OUTLINE
•
•
•
•
•
1)
2)
3)
4)
5)
review roman numerals
review apothecary measurements
review conversions
review 3 steps to dosage calculations
practice, practice, practice
• 
Plugging in to Memory
• Roman Numerals
APOTHECARY MEASURES
– What are we talking about?
CONVERSIONS
• - WITHIN SYSTEMS
• - BETWEEN DIFFERENT SYSTEMS
WITHIN SYSTEMS
• MEMORIZE:
•
•
•
•
1 gram (g or G) = 1000 milligrams (mg)
1 liter (l or L) = 1000 milliliters (ml or mL)
3 teaspoons (t) = 1 tablespoon (T)
1 cubic centimeter (cc) = 1 milliliter (ml)
BETWEEN SYSTEMS
•
•
•
•
•
•
•
•
MEMORIZE:
1 gram (G, GM, gm) = 15 grains (gr)
60 milligrams (mg) = 1 grain (gr)
1 tablespoon (T) = 15 ml
1 kilogram (kg) = 2.2 pounds (lb)
1 ounce (oz) = 30 ml or 30 cc
1 cc = 15 drops (gtt) or 15 minims (mx)
1 inch (in) = 2.5 centimeters (cm)
STEPS TO CONVERSION
WITHIN SYSTEMS
• 1) Write down what you know in a ration
or fraction format:
– Example: 1 Gram
–
1000 milligrams
• 2) Write down what you desire in a ratio or
fraction format to complete the proportion:
• Example: 3 Grams
•
x milligrams
• Remember:
• The numerator and denominator must be the
same unit of measurement
• The unknown value is referred to as “x”
The completed proportion:
•
•
1 Gram
1000 mg : :
• Cross multiply
3 Grams
x milligrams
• 1 GM x X mg(s) = 3 GM x 1000 mg
• Drop the terms used for units of
measurement: 1 X = 3(1000)
• Solve for X: divide both sides of the
equation by the number preceding X:
• X = 3000
• 1
1
X = 3000
BETWEEN SYSTEMS
• 1) Write down what you know in a fraction
format:
•
•
15 grains
1 gram
• 2) Complete the proportion by writing
down what you desire:
•
•
15 grains
1 gram : :
30 grains
X grams
• HINT: Keep the units of measurements in
the correct spaces!
• Drop the units of measurement
• Cross multiply
•
•
15 x X = 30 x 1
15X = 30
• Solve for X: Divide each side by the number in
front of X : 1 X = 2
ANS: 2 Grams
VOILA!!
3 STEPS TO DOSAGE
CALCULATION:
• 1) Convert to units of same system and
similar unit
• 2) STOP AND THINK
• 3) Desired over amount on hand times
quantity
• EX: desired
•
amount on hand x
quantity
SAMPLE PROBLEMS
– 1) Convert: 300 mg to grams
– 2) Convert: 120 mg to grains
– 3) Convert: 30 gr to grams
– 4) A child who weighs 55 pounds weighs ____
–
kilograms?
• 5) A patient is restricted to four 8-ounce
glasses of water per day. The nurse knows
that the patient’s fluid intake is restricted to
____ mls per day.
• 6) The nurse administered aspirin gr v. She
knew this was equivalent to
_____milligrams(s).
• 7) Potassium chloride tablets are available
in 300 mg doses. The physician prescribed
gr v. Give ____ tablet(s).
• 8) The physician prescribed Capoten, 1.5
grams daily in three equal doses, for
hypertension. The nurse would give _____
1000 mg tablet(s) three times a day.
• 9) Lasix 30 mg, IM, is prescribed as a diuretic.
Lasix was available as 40 mg/mL. The nurse
would give ______mL.
• 10) Scopolamine 0.3 mg was ordered
subcutaneously as a preanesthetic medication.
The medication was available in ampules
containing grains 1/200 per mL. The nurse would
give _____mL.
• 11) The physician prescribed 25 mg of Librium,
IM. Add 2 mL of diluent to yield 100 mg/2ML.
The nurse should give _____ mL.
• 12) The physican prescribed 5 mg of Garamycin
for a child. The medication is available as 20
mgs/mL. To give 5 mg, you would give ____ mL.
PRACTICE, PRACTICE,
PRACTICE
• And HOLLER if you need help!