Drugs are only safe when administered with the correct dose, many drugs do not come from the pharmacy prepared so it is up to you as the health care professional to calculate how much to give based on the concentration the pharmacy has available.
Drug Calculation ConversionsDrugs are measured by weight like, Grams (gm) or Milligrams (mg) or liquid volumes like, Milliliters (mL) or Liters (L). Drugs also can be given in a household measuring units such as ounces (oz) or teaspoons (tsp) that have to be converted.
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It is important that you memorize these conversions as it is your responsibility as the health care professional to administer drugs safely and accurately to prevent errors. This is one of the eight "rights" - Right dose.
knowing how to convert measurements can insure the correct amount of the drug is given. |
It is also important to know how decimals and rounding work as when working your drug calculation both will be emanate.
- Always put a zero before the decimal for numbers less than one (0.3 not .3)
- Never leave training zeros after a whole number (3 not 3.0)
- When rounding a number followed by a 5 or larger is rounded up. A number 4 or below are left the same. (8.15=8.2; 6.14=6.1)
- Make sure you round all answers to the tenth place except gtt/min which will be rounded to a whole number
- And never round until you are finished with your problem otherwise this will not provide you with the correct administration amount
How to solve dosage calculations |
Dosage Calculations are preformed in the same way weather the drug is a tablet, oral liquid, injectable liquid, or suppository. The best way to calculate drugs is with dimensional analysis. On the right hand side you can find the steps on how to do so.
Lets try it!A patient who weighs 220 lb is prescribed a dose of medication at 12.5 mg/kg of body weight. The concentration of the medication on hand is 125 mg/mL, and the patient wants to take the medication orally, by teaspoon. How many teaspoons of medication will the patient need to take per dose?
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Step One: Convert the patients weight to kg. 1kg=2.2lb
220lbX 1kg = the Patient weighs 100kg
1 2.2lb
220x1= 220
1x2.2= 2.2
220/2.2= 100
Step Two: The amount of medication needed based on body mass is 12.5mg/kg so, you would essentially multiple 12.5mg/kg X 100kg = 1250mg
Step Three: 1 tsp = 5mL, so the conversion ratio is 5ml/tsp so the concentration is teaspoons is now 125mg/mL X 5 mL/tsp=625mg/tsp
Step Four: The final dose in teaspoons is 1250 mg divided by 625mg/tsp = 2tsp per dose
Workman, M. L., & LaCharity, L. A. (2016). Understanding pharmacology: Essentials for medication safety. St. Louis, MO: Elsevier. Page 72
220lbX 1kg = the Patient weighs 100kg
1 2.2lb
220x1= 220
1x2.2= 2.2
220/2.2= 100
Step Two: The amount of medication needed based on body mass is 12.5mg/kg so, you would essentially multiple 12.5mg/kg X 100kg = 1250mg
Step Three: 1 tsp = 5mL, so the conversion ratio is 5ml/tsp so the concentration is teaspoons is now 125mg/mL X 5 mL/tsp=625mg/tsp
Step Four: The final dose in teaspoons is 1250 mg divided by 625mg/tsp = 2tsp per dose
Workman, M. L., & LaCharity, L. A. (2016). Understanding pharmacology: Essentials for medication safety. St. Louis, MO: Elsevier. Page 72
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