Equivalents / Conversions
Many times a drug is prescribed in a unit of measure different than the unit available. For example, so many fluid ounces of a liquid medication is ordered to be given in teaspoonful increments; you have the medication, but in one pint bottles and with a medicine cup for administration, calibrated in milliliters. How much do you dispense? How much does the patient take? As a pharmacy technician, you will need to know how to make conversions between the different systems of measurement. The simplest way to convert measurements from one system to another is to set up a ratio and proportion equation.
To do this, it is necessary to first check a table of conversions to determine the equivalent measure in the two systems you are using. It must be remembered that equivalent values are just that, equivalent - almost but not quite equal. A common example of such a discrepancy is between the metric and apothecary systems. Depending on the conversion chart used, you may find that 60 - 65 mg equals 1 grain. Let's say we have a prescription calling for a 5 grain dose of a particular medication that needs to be converted to milligrams, the dosage may vary from 300 to 325 mg. Depending on the drug and the accuracy required, another conversion may need to be employed making the conversion more accurate, such as 1 gr = 64.8 mg, which in this example yields a 324 mg dose. You must realize that discrepancies are exponential and care should be taken when choosing a conversion table.
|Metric System||Apothecary System||Household System|
|28.35 g||437.5 gr||1 oz|
|1 kg||---||2.2 lb|
|453.59 g||---||1.0 lb|
|1 g = 1000 mg||15 gr (gr xv)||---|
|64.8 mg||1 gr (gr i)||---|
|30 mg||1/2 gr (gr ss)||---|
|1 L = 1000||33.8 fl oz||about 1 qt|
|473 mL||16 fl oz (fl oz xvi)||1 pt|
|355 mL||12 fl oz (fl oz xii)||---|
|237 mL||8 fl oz (fl oz viii)||1 c|
|29.57 mL||1 fl oz (fl oz i)||2 tbsp|
|15 mL||---||1 tbsp = 3 tsp|
|8 mL||---||2 tsp|
|5 mL||---||1 tsp = 60 gtt|
|3.7 mL||1 fl dr (fl dr i)||---|
|1 mL||15 min (min xv)||---|
|0.07 mL||1 min (min i)||---|
Conversion tables can vary, one from the next, so make sure you are using the conversion table(s) adopted by your particular pharmacy. When conversions are used frequently, it is easy to remember them. When conversions are not used frequently, it is always best to look them up.
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