When it comes to medication and dosages, nurses have to keep track of the number of times, and the quantity, when administering drugs to patients. On top of that, performing correct dosage calculations is critical in the nursing profession. Mastering it is a key aspect in a nurse’s practice. If you are already a nurse, or have just stepped into the profession, you should be well aware of the basics related to every drug dosage calculation.
Abbreviations rule the medical world. Thus, it is important to know the recognized abbreviations in a clinical setting so you will not be lost when preparing patients’ medications. Here are some:
In calculating tablet dosages, the following formula is useful: Desired dosage ÷ stock strength = number of tablets
The desired dosage is the dosage ordered by the physician, while the stock strength is the amount of drug present in each tablet. Stock strength is also known as stock dose.
The following formula is useful in calculating mixtures and solutions: Desired dosage ÷ stock strength x stock volume = amount of solution to be given
The desired dosage is the dosage ordered by the physician. The stock strength is the amount of drug present in the preparation, while the stock volume is the amount of the solution where the drug is diluted.
Example:It is easy to calculate the running rate of IV fluids in terms of mL per hour or mL per minute: Total IV volume ÷ time (hour or minute) = mL per hour or minute
The total IV volume is the amount of fluid to be infused while the time is the number of running hours or minutes.
Example:Calculating for drops per minute is simple with the following formula: [Total IV volume ÷ time (minute)] x drop factor = drops per minute
The total IV volume is the amount of IV fluid to be infused while time is the duration of how long the IV fluid should be infused in terms of minutes.
The drop factor is the "drops per millilite" delivered to the patient and it depends on the macrodrip used for the infusion. The common drop factors used in different hospitals are 10, 15 and 20.
Example:Calculating for the remaining time of infusion for a certain IV fluid is possible with the following formula: [Volume remaining (in mL) ÷ drops per minute] x drop factor = minutes remaining
The volume remaining is the amount of IV fluid remaining for the infusion. The drops per minute is the regulation of the IV infusion. The drop factor can be determined in the macrodrip used in the hospital.
Example:If you know the basic drug calculation formulas, you will never be lost in finding the desired dosage for your patient.It’s best to master drug calculations and know the unit conversions. Once you start working in a clinical setting, you will get used to the common formulas used in determining desired dosages or IV regulations. It takes a lot of practice to master drug calculations in a short period of time, nursing pharmacology will then be a piece of cake for you.
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