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 Âµg/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 Âµg/min

625 Âµg = 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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