A Basic Guide to Mastering Essential Pharmacy Math Skills

One of the many responsibilities of a Pharmacy Technician generally involves prescription filling, inventory management, and assisting customers with medication orders. A basic math competency is imperative in safely and adequately dispensing medication. In this guide, I cover the essential math skills that a pharmacy technician needs to know, with simple explanations and examples.

Understanding Measurements

Pharmacy technicians prepare medications using many different types of measurements. Some standard units of measurement in pharmacy include milligrams (mg), grams (g), milliliters (mL), and liters (L).

What is Mass?

Medications are commonly weighed by mass. The two most frequently used units of measurement are milligrams and grams. For instance, a prescription is written for 500 mg of a medication. Remember that 1 gram = 1000 milligrams. Therefore, 500 mg is half a gram.

Volume Medications can be ordered to give a specific volume. 

Examples of volume measurements include milliliters (mL) or liters (L). If you have a prescription to take 10 mL of a liquid medication, you must know how to measure a volume of 10 mL.

It is necessary to know the difference between these units and be able to convert among them. For example:

1 gram = 1000 milligrams

1 liter (L) = 1000 milliliters (mL)

Converting Units of Measurement

Sometimes, you will need to convert from one unit of measurement to another. Here are some key conversions that you will want to keep in mind:

Mass:

1 gram = 1000 milligrams

1 kg = 1000 g

Volume:

1 liter (L) = 1000 milliliters (mL)

1 mL = 1 cc (cubic centimeter)

Liquid to Solid 

Some medications must be converted between a liquid and solid measurement. For example, if the medication is 50 mg per mL and the physician ordered 150 mg, you will want to know how much liquid to administer.

Formula: Volume = Dose / Concentration Thus, for example:

Volume = 150 mg / 50 mg per mL = 3 mL

Dosage Calculations

Dosage calculation is the most critical activity that pharmacy technicians are entrusted with. The patient is still expected to be prescribed the right amount of the drug. The dosages can be calculated using a simplified method as shown in the desired overhang formula:

(Desired dose ÷ Available dose) × Available volume = Amount to give

For example, if the physician orders 250 mg, and you have a supply of the medication in 500 mg tablets, your calculation would be D250mg desired dose/have a dose of 500mg ×1 tablet has volume = ½ tablet. Hence, the patient would have only needed to take half a tablet.

Know Your Percentages

One needs to understand and calculate the concentration of a drug, especially in liquid medications. This is usually expressed in percent. For example, a 10% solution contains 10 g of active ingredient in each 100 mL solution.

Thus, you can do the arithmetic using this formula from now on to obtain the actual volume of the active ingredient.

Quantity of active ingredient = (percentage / 100) × Volume

If you have a 20% solution, and you need to give 50 mL, the calculation would be:

The solution would contain 20 / 100 x 50 = 10 grams of active ingredient.

Interpreting the Drug Label

Lastly, pharmacy technicians should know the method of reading and interpretive analysis of the labeled names on drugs. A general drug label would contain the name of the medication in question, strength, amount/dosage, and other information—Amoxicillin 250mg Capsules – 30 Capsules. This label thus translates to each capsule bearing 250 mg of active ingredient amoxicillin within its core and a collection totaling up to thirty capsules inside the medication bottle.

Understanding how to interpret the information given is essential, as it will allow for Knowing the dose of medication to administer and Having the right amount for the prescription. If you are asked to dispense a certain amount of capsules, you can check immediately if that amount is correct by reading the label.

IV Flow Rate Calculations

Pharmacy technicians are often asked to perform flow rate calculations for IV medications. If you prepare an IV, you need to know the rate at which the medication is delivered to the patient. 

The flow rate is generally expressed in milliliters per hour or mL/hr.

The formula used in determining the flow rate is :

Flow rate (ml/hr) = Total volume (ml) / Time (hrs)

Example: For medications to be given over 4 hours at a volume of 500 mL:

500 mL / 4 hrs = 125 mL/hr

Therefore, the IV should be adjusted to flow at 125 mL/hour.

Rounding and Estimating

Sometimes, when measuring medication, you will be asked to round a number to the nearest whole number or a decimal place. For example, if asked to give 5.67 mL, you would round that to 5.7 mL or even 6 mL, depending on the directions.

Estimating is another essential skill. If you are unsure about a calculation, being able to estimate will ensure you’re close to the correct answer. Always double-check your work to make sure you did everything correctly.

Conclusion

Understanding basic mathematics is essential for pharmacy technicians, as it aids in dispensing drugs, correct dosing calculations, and patient security. A strong math background prevents errors, keeps inventories under control, and adheres to prescriptions accurately.
If you’re contemplating a career in pharmacy technology, mastering these skills is a great beginning. To learn more about such a career, visit Northwest Career College.