Step 1: Convert inputs to common units.
Step 2: Solve equation.
X = (D / H) × Q
X = (75 / 100 mg) × 2 mL
Result = 1.5 mL to inject
Parenteral administration refers to delivering medications by injection (intravenous, intramuscular, subcutaneous, or intradermal routes). The formula D/H × Q determines the volume of solution to draw up in a syringe.
The “Desired” dose is what the prescriber ordered. The “Have” dose is the concentration available on the medication vial label. The “Quantity” is the volume that contains the Have dose.
Calculate Parenteral Dosage ↑Order: 250 mg of a drug IM. Available: 500 mg per 2 mL.
X = (250 / 500) × 2 = 1 mL
D is the Desired dose (what the doctor ordered), H is the Have dose (the amount of drug per unit on the vial), and Q is the Quantity (the volume that contains H). This formula gives you the volume to draw up and administer.
The Desired and Have doses must be in the same units before applying the formula. This calculator automatically converts between mg, g, and mcg so you can enter values in whichever unit they are prescribed or labeled.