Calculate A Dose
Apply emergency or public-health rules to calculate a dose.
- Read a protocol: Emergency decisions must follow the stated rule in order.
- Balance benefit and risk: Interventions should help while minimizing harm.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Use Volume = Dose / Concentration with new numbers. Keep the ordered dose on top and the concentration on the bottom.
| Quantity | Symbol | Unit |
|---|---|---|
| Dose ordered | D | mg |
| Concentration on hand | C | mg/mL |
| Volume to give | V = D / C | mL |
An order calls for 150 mg of a medication. The vial is labeled 50 mg/mL. Using Volume = Dose / Concentration, how many mL should be given?
Reviewed| Quantity | Symbol | Unit |
|---|---|---|
| Dose ordered | D | mg |
| Concentration on hand | C | mg/mL |
| Volume to give | V = D / C | mL |
- A.3 mL
- B.2 mL
- C.100 mL
- D.7500 mL
Show the worked solution ▾
Answer: A. 3 mL
- Step 1: Plug in: Volume = 150 mg / 50 mg/mL.
- Step 2: Divide: 150 / 50 = 3, so the volume is 3 mL.
Why it's right: 150 mg divided by 50 mg/mL equals 3 mL.
- B: 2 mL would be 100/50; this order is 150 mg, not 100 mg.
- C: 100 mL comes from subtracting (150 - 50) instead of dividing.
- D: 7500 mL comes from multiplying 150 by 50 instead of dividing.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
- A nurse computes 3 mL from a 150 mg order of a 50 mg/mL drug before drawing it up.
Fill these in as you work through the lesson.
- Dose (amount of drug ordered, in mg):
- Concentration (mg of drug per mL of liquid):
- Volume (how many mL to give):
- Unit conversion (1 g = 1000 mg):
Volume (mL) = (mg) divided by (mg/mL); if the order is in grams, first convert using 1 g = mg.
- What is the ordered dose, and in what unit?
- What is the concentration on the label?
- Do the units match, or do you need to convert grams to mg first?
Order: 200 mg. Vial: 100 mg/mL. Volume = 200 / 100 = 2 mL.