Dose Calculation for Partial Volume Administration
When administering 30 mL of a solution containing 3000 mg in 100 mL, you will deliver 900 mg.
Calculation Method
The concentration of this solution is 30 mg/mL (3000 mg ÷ 100 mL = 30 mg/mL). Therefore:
- 30 mL × 30 mg/mL = 900 mg
This represents 30% of the total volume and 30% of the total drug content.
Clinical Application Framework
When performing medication calculations in clinical practice, always use this systematic approach:
- Determine the concentration by dividing total drug mass by total volume (mg/mL or mcg/mL) 1
- Multiply the concentration by the desired volume to calculate the dose being administered 1
- Double-check calculations using the ratio method: if 100 mL contains 3000 mg, then 30 mL contains (30/100) × 3000 mg = 900 mg 2
Critical Safety Considerations
Always verify your calculations independently before drug administration, as dosing errors represent the most common type of medication error and can result in significant patient harm 3. Medical students and nurses frequently struggle with drug calculations, with studies showing only 10% of clinical medical students answering basic concentration questions correctly 2.
- Use consistent units throughout your calculation to avoid errors by factors of 10,100, or even 1000 2
- Express concentrations as mass per unit volume (e.g., mg/mL) rather than ratio expressions (e.g., 1:1000) to minimize confusion 2
- Consider using a calculator for complex calculations, though understanding the underlying mathematical principles remains essential for detecting errors 3
Verification Strategy
For this specific example, verify using multiple methods:
- Method 1 (concentration): 30 mg/mL × 30 mL = 900 mg
- Method 2 (proportion): 30 mL is 30% of 100 mL, so 30% of 3000 mg = 900 mg
- Method 3 (ratio): 3000 mg/100 mL = X mg/30 mL, solving gives X = 900 mg