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Information

  1. COMMON METRIC CONVERSION
    1. Weight:
      • 1 gram (gm) = 1,000,000 micrograms (mcg)
      • 1 milligram (mg) = 1,000 micrograms (mcg)
      • 1,000 milligrams (mg) = 1 gram (gm)
      • 1 kilogram (kg) = 1,000 grams (gm)
    2. Volume:
      • 1 liter (L) = 1,000 milliliters (mL)
      • 1 kiloliter (kL) = 1,000 liters (L)
      • 1 milliliter (mL) = 1 cubic centimeter (cc)
  2. APOTHECARY SYSTEM (Note: metric is preferred for medication administration.)
    1. Weight:
      • 60 grains (gr) = 1 dram (dr)
      • 8 drams (dr) = 1 ounce (oz)
    2. Liquid:
      • 60 minims = 1 fluidram (fl dr)
      • 8 fluidrams (fl dr) = 1 fluidounce (fl oz)
      • 16 fluidounces (fl oz) = 1 pint (pt)
      • 2 pints (pt) = 1 quart (qt)
      • 4 quarts (qt) = 1 gallon (gal)
  3. EQUIVALENT HOUSEHOLD CONVERSIONS
  4. DETERMINING EQUIVALENCY FROM ONE SYSTEM TO ANOTHER
    Use a proportion. On the left side of the proportion is what you know to be an equivalent (e.g., 30 milliliters equals 1 ounce). On the right side of the proportion is what you need to determine (e.g., you want to give 1.5 ounces and your medicine cup is in milliliters—you would write "x" milliliters equals 1.5 ounces). Rewrite the proportion without using the symbols.
    Example:
    1 oz : 30 mL :: x mL : 1.5 oz
    Solve for x:
    1x = 30 × 1.5
    x = 45
    1.5 ounces equals 45 milliliters (mL)
  5. ALTERNATE FORMULA FOR CALCULATION WITH LIKE UNITS
    D (Desired Amount)/A (Available Amount) × Q (Quantity Available) = x
    Example: the order is for 50 mg of phenobarbital, which comes in 20 mg per 5 mL.
    50 mg (Desired)/20 mg (Available) × 5 mL (Quantity)/1 = x
    Solve for x:
    x = 50/20 × 5/1
    x = 50 × 1/4 × 1
    x = 50/4
    x = 12.5 mL
  6. DIMENSIONAL ANALYSIS FOR CONVERSION AND CALCULATION
    Another format for dosage calculation that uses only one equation even when conversion to like units is needed.
    Example with like units: penicillin 500 mg comes in 250-mg capsules. You would give _______ capsules. On the left side of the equation is the drug form you are solving for:
    x capsules =
    On the right side, place the known information in a common fraction with the numerator matching the x quantity (capsules). The amount in each capsule that is known is the denominator (250 mg):
    x capsules = 1 capsule/250 mg
    Next set up a proportion with the information that matches the denominator (500 mg):
    x capsules = 1 capsule/250 mg × 500 mg/1
    x = 1 × 500/250
    x = 2 capsules
    Example with different units: Keflin 400 mg IM q10h. The drug is available in 0.5 gm per 2 mL.
    x mL = 2 mL/0.5 g
    Because the available drug is in grams (gm), an additional fraction is added for the conversion from grams to milliliters. Remember: the numerator of each fraction must match the denominator of the fraction before.
    x mL = 2 mL/0.5 g × 1 g/1,000 mg
    x mL = 2 mL/0.5 g × 1 g/1000 mg × 400 mg/1
    (amount of drug ordered)
    Cancel out the like abbreviations on the right side of the equation. If the equation is correct, the only abbreviation remaining on the right side will match the abbreviation on the left side (mL):
    x mL = 2 mL/0.5 g × 1 g/1000 mg × 400 mg/1
    Solve for x:
    x = 2 × 400/0.5 × 1000
    x = 800/500
    x = 1.6 mL
  7. DETERMINING FLOW RATES FOR PARENTERAL INFUSION (see Intravenous Therapy, II. B, Physiological Integrity).