Medication Calculation Quick Review By Collette Loftin MSN RN

Review :

Review Oral solids – tablets
Calculation of injectable medications
IV – continuous infusions of medications
IV – drip rates

Dosage Calculation :

Dosage Calculation In dosage calculations, three pieces of information are given:
The Dr. order (desired amount)
Quantity or strength of drug on hand
Solid or liquid form of drug on handThe unknown is the amount of drug to administer

Rule for Calculating :

Rule for Calculating Formula for calculating is:
D ÷ H x S = Amount

Liquid Injection Order: Demerol 75 mg IM
Supply: See Label

Liquid Injection :

Liquid Injection 75mg÷50mg X 1 = 1.5 ml

Intravenous (IV) calculations :

Intravenous (IV) calculations Example:
An order is written for 50,000 units of heparin in 500 ml of D5W to infuse at 800units/hr, what is the correct rate of the infusion (in ml/hr)?
800u/hr ÷ 50,000u X 500 mL = 8 mL/hr

Problems :

Problems Order: Heparin 1100units/hr IVSupply: Standard solution: 25,000 units Heparin in 250 mL D5W
1100u/hr ÷ 25,000u X 250 mL = 11 mL/hr
Order: regular insulin 10units/hr IVSupply: Standard solution: 125 units regular insulin in 250 mL NS
10u/hr ÷ 125u X 250 mL = 20 mL/hr

Calculating mg/minute problems :

Calculating mg/minute problems Order: Drug ABC 1mg/minSupply: Infusion pump, standard solution of 1 g in 500 mL D5W1 mg/min = 60 mg/hr60 mg/hr ÷ 1000 mg X 500 mL =30 mL/hr

mg/kg/min or mcg/kg/min :

mg/kg/min or mcg/kg/min Solved same as mcg/min
First, must weigh patient and multiple ordered amount of drug X pt. weight
Example:
Order: Drug XYZ 2 mcg/kg/min
Pt weighs 176 pounds or 80 kg
Order is now 2 X 80 = 160 mcg/min

Drip Rates (gtts/min) :

Drip Rates (gtts/min) mL per hour X tubing drip factor = gtts/min
60 (minutes in hour)
Example: IV is infusing at 125 cc/hr. How many drops per minute if using 15 gtt tubing?
125 mL X 15 = 31 gtts / minute 60 minutes

IV drip rate :

IV drip rate Order: 500 mL D5W to run from 0100–0500.
What is the hourly rate? __________
What is the drip rate with 15 drop tubing? ___________

Converting Grains :

Converting Grains 60 mg = 1 gr
So, if we have an order to give Drug ABC gr1/150,
we will divide 60 by 150 = 0.04mg.
Likewise, gr 1/6 = 10mg
and gr 1/4 = 15mg
Aspirin and Tylenol calculate 65 mg = 1 grain

Practice Problem :

Practice Problem Ordered: Drug ABC 400 mg IVPB in 100 ml of D5W q6hAvailable: 1 gram vial of powder . Label reads: For IV infusion, add 3.5 ml NS. Resulting solution contains 250 mg of Drug ABC per ml. Use solution within one hour.How many ml of the dissolved Drug ABC will you add to the 100 ml bag?

Practice Problem :

Practice Problem Drug ABC 400mg IVPB q 6hrs
Supply of 250mg/1ml
400 mg ÷ 250 mg x 1 ml = 1.6 ml
So, in this problem we will add 1.6 ml to our bag of fluid to be infused.

Questions? :

Questions? Email
cloftin@wtamu.edu
Or
Call 651-2629

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