Top Formulas for Pharmacy Technicians

1. Dosage Calculation

This formula is used when you want to find out the dosage of a medication.

Dosage = (Desired Dose / Stock Dose) * Stock Volume

• Desired Dose: The dose as prescribed by the doctor
• Stock Dose: The dose present in each tablet or each ml of liquid
• Stock Volume: The volume of liquid or number of tablets

2. Percentage Strength

This is used to calculate the strength of a solution as a percentage.

Strength % = (Weight of solute / Volume of solution) * 100

3. Dilution Calculation

This formula is used when a concentrated solution needs to be diluted to a weaker strength.

C1 * V1 = C2 * V2

• C1 = Initial concentration
• V1 = Initial volume
• C2 = Final concentration
• V2 = Final volume

4. BMI Calculation

Body Mass Index (BMI) is a simple calculation using a person's height and weight.

BMI = Weight (kg) / (Height (m))^2

Or

BMI = (Weight (lb) / (Height (in))^2) * 703

5. Creatinine Clearance

Creatinine clearance is used to estimate the glomerular filtration rate (GFR). This is done using the Cockcroft-Gault Equation:

For men: Creatinine Clearance = [(140 - age) * weight (kg)] / (72 * serum creatinine)

For women: Creatinine Clearance = [(140 - age) * weight (kg) * 0.85] / (72 * serum creatinine)

6. Pediatric Dose Calculations

When administering medication to children, doses are often adjusted according to the child's body weight or body surface area (BSA).

For weight-based dosing:

Dose (mg) = weight (kg) * dose (mg/kg)

For BSA-based dosing (using the Mosteller formula for BSA):

BSA (m2) = SQRT( [Height(cm) * Weight(kg) ]/ 3600 )

Then,

Dose (mg) = BSA (m2) * dose (mg/m2)

Remember to always check and double-check your calculations and follow your pharmacy's guidelines. Incorrect calculations can lead to serious medication errors.