Dosage Calculation: 13mg from 50mg/mL Solution
You need to administer 0.26 mL of the 50mg/mL solution to deliver 13mg.
Calculation Method
The volume required is calculated using the basic formula:
Volume (mL) = Desired Dose (mg) ÷ Concentration (mg/mL)
- Desired dose: 13 mg
- Concentration: 50 mg/mL
- Volume needed: 13 mg ÷ 50 mg/mL = 0.26 mL
Critical Safety Considerations
Always verify the concentration labeling format before drawing up any medication. Drug concentrations expressed in different formats (ratios, percentages, or mg/mL) are a major source of confusion and dosing errors among healthcare providers 1.
Key Safety Points:
Double-check decimal placement - Errors in decimal point placement can result in 10-fold dosing errors, which is particularly dangerous in pediatric patients 2.
Confirm the concentration - Studies show that only 65.8% of physicians correctly identified drug concentrations when expressed as percentages, and 85.2% when expressed as ratios, compared to 93.1% accuracy with mg/mL labeling 3.
Use appropriate measuring devices - For volumes less than 1 mL, use a 1-mL syringe with 0.01 mL graduations to ensure accurate measurement 1.
Independent verification - Have a second provider verify both your calculation and the drawn-up dose, especially for high-risk medications 4.
Common Pitfalls to Avoid
Confusing concentration formats: The mg/mL format is the clearest and least error-prone method of expressing drug concentrations 3.
Mathematical errors: Studies demonstrate that 27% of medical students answered all dosage calculation questions incorrectly, with a mean score of only 1.24 out of 3 4.
Calculator dependency: While calculators reduce arithmetic errors, understanding the underlying calculation is essential for catching input errors 5.