Drug dose calculation is a most common calculation for pharmacy student, pharmacy technician and compounding or dispensing pharmacist. A dispensing pharmacist must dispense the drugs in the right doses and accurate concentrations to ensure the patient safety.
Common formula of Drug Dose Calculation
D/H × Q = X
Here,
D = Desired dose
H = Amount have on hand
Q = Quantity
X = Amount to be given
Drug Dose Calculation Example
1. Lidocaine is ordered 1 mg/kg to a patient that weighs 150 lbs. It is supplied 100 mg/5 mL. How many mL will you need to give?
150 lbs = 68 kg
So, Desired Dose (D) = 68 mg
Amount have on hand (H) = 100 mg
Quantity (Q) = 5 ml
Thus, Amount to be given (X) = D/H × Q = 68×5/100 = 3.4 ml
2. Omeprazole is ordered 20 mg IV. It is supplied 40 mg/ 5 mL. How many mL will you need to give?
Amount to be given (X) = D/H × Q = 20×5/40 = 2.5 ml
Related: Concentration and Dilution Calculation in Pharmacy
Desired Dose Calculation Example
1. A pediatric patient is to receive Atropine 0.01 mg/kg. The patient weight is 18 Kg. What is the desired dose?
0.01 × 18 = 0.18 mg
2. A patient with hypotension is ordered to receive Dopamine at 5 µg/kg/min. The patient weight is 275 Lbs. Your Dopamine is mixed 800 mg in 500 mL. What is the desired dose?
275 lbs = 125 kg
5 × 125 = 625 µg/min
625 µg = 0.625 mg
As, 800 mg in 500 mL
Thus, 0.625 mg in 1 ml.
So, Desired dose is 1 ml.
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