Describe the three basic steps for calculating the prescribes dose of medicine accurately

1.  Convert-

      - All measurements are to be in the same system of measurement.

      - Convert to the measurement of your supply.

      - 1 grain= 60 milligrams

      - 1 gram= 1000 milligrams

2. Think-

      - Estimate what is a reasonable amount of the drug to be given.

      - Oral tabs/caps should be whole or half

3. Calculate

      - Use the formula

    D x Q = X

    H

D is the order

H is the supply

Q is the quantity (will always be found after the {per})

X is the amount to give

Introduction

There are 3 primary methods for calculating medication dosages; Dimensional Analysis, Ratio Proportion, and Formula or Desired Over Have Method. We will explore the Desired Over Have or Formula Method, one of these 3 methods, in more detail.

Desired Over Have or Formula Method uses a formula or equation to solve for an unknown quantity (x), much like ratio proportion.

Calculations require using conversion factors, for example, when converting from pounds to kilograms or liters to milliliters. Simplistic in design, this method allows clinicians to work with various units of measurement, converting factors to find the answer. These methods are useful in checking the accuracy of the other methods of calculation, thus acting as a double or triple check.  

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Preparation

When clinicians are prepared and know the key conversion factors, they will be less anxious about the calculation involved. This is vital to accuracy, regardless of which formula or method is employed.

Conversion Factors

1 kg = 2.2 lb

1 gallon = 4 quart

1 tsp = 5 mL

1 inch = 2.54 cm

1 L = 1,000 mL

1 kg = 1,000 g

1 oz = 30 mL = 2 tbsp

1 g = 1,000 mg

1 mg = 1,000 mcg

1 cm = 10 mm

1 tbsp = 15 mL

1 cup = 8 fl oz

1 pint = 2 cups

12 inches = 1 foot

1 L = 1.057 qt

1 lb = 16 oz

1 tbsp = 3 tsp

60 minute = 1 hour

1 cc = 1 mL

2 pints = 1 qt

8 oz = 240 mL = 1 glass

1 tsp = 60 gtt

1 pt = 500 mL = 16 oz

1 oz = 30 mL

4 oz = 120 mL  

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