The notation "400mg/5mL" on your child's medication bottle isn't just a label—it's the key to accurate dosing. Understanding this concentration is the difference between an effective dose and a potentially dangerous error.
What Is a Medication Concentration?
A medication concentration tells you how much active drug is dissolved in a specific volume of liquid. When you see "400mg/5mL" on an Amoxicillin bottle, it means that every 5 milliliters of liquid contains 400 milligrams of the actual antibiotic.
Think of it like making lemonade: the concentration is how much lemon juice is in each cup of water. A more concentrated solution has more "active ingredient" per unit of liquid.
Key insight:
The same medication can come in different concentrations. Amoxicillin, for example, is commonly available in 125mg/5mL, 250mg/5mL, and 400mg/5mL formulations. Using the wrong concentration in your calculation can result in giving 2-3x the intended dose.
Reading the Concentration Format
Every liquid medication concentration follows a standard format:
Why Concentrations Matter for Safety
Medication errors involving liquid formulations are 5 times more common than errors with solid dosage forms like tablets. The primary culprits are:
- Confusing different concentrations: A parent with a 250mg/5mL bottle from a previous prescription might calculate a dose meant for 400mg/5mL.
- Mathematical errors: Converting a prescribed mg dose to mL volume requires division—a step where mistakes happen.
- Incorrect measuring tools: Using kitchen spoons instead of calibrated oral syringes introduces up to 40% variance.
The Dosage Calculation Formula
To convert a prescribed dose (in mg) to a volume (in mL), use this universal formula:
Example Calculation
Your pediatrician prescribes 250mg of Amoxicillin. You have a bottle labeled 400mg/5mL. How many mL do you give?
Common Medication Concentrations
Here are the most frequently prescribed liquid medications and their typical concentrations: