Nursing 104

N104: Essentials of Nursing Care – Health Safety Study Guide with the liter, and its subdivision of the milliliter (mL), and the kilogram, and its subdivisions of the gram (Gm), milligram (mg), and microgram (mcg). When writing medication dosages in metric units, prescribers and nurses use either fractions or multiples of a unit. Fractions should be converted to their equivalent decimal form. A zero should be placed in front of the decimal to prevent error. For example: 500 mg or 0.5 g, not 1/2 g or .5 g. Trailing zeroes should be avoided when writing metric dosages (e.g., 14.0 mg should be written as 14 mg). A trailing zero has been associated with dosage errors. For example, 10.0 mg could be confused for a dose of 100 mg. A zero to the right of the decimal should be avoided. Always use a zero before a decimal point. The household system is typically the measurement system used when instructing patients on home use of medications. Although, not as accurate as the metric system, it is more widely understood in the U.S. with the use of drops (gtt), teaspoons (tsp), tablespoons (T), ounces (oz), and cups (C). Dosage Conversions Medications are often dispensed in units of measure different than that in which they are ordered. The nurse must convert available units of volume and weight to desired doses. Common conversions that will be useful to the nurse are: • 1000 mcg = 1 mg • 1000 g = 1 kg = 2.2 lb • 1 mL = 15 drops (gtt) • 4 to 5 mL = 1 tsp • 15 to 16 mL = 3 tsp = 1 tbsp • 30 mL = 1 fluid oz = 2 tbsp • 240 mL = 8 fluid oz = 1 cup • 1000 mL = 1 L Medication measuring cups are often marked in both the metric and household systems.

Dosage Calculations Dosage calculations are necessary when the dose on the medication label differs from the dose ordered. There are several methods for calculating doses. The most common method is the ratio-

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