Liquid Medications¶
Overview¶
Liquid medications are used when patients cannot swallow tablets or capsules, for pediatric patients, and for medications that are only available in liquid form. The calculation method is identical to tablets — unit cancellation — but the answer is a volume (mL) rather than a count.
Reading Liquid Medication Labels¶
Liquid medications are labeled as a concentration:
| Label | Meaning |
|---|---|
| 250 mg/5 mL | 250 mg of drug in every 5 mL of liquid |
| 125 mg/5 mL | 125 mg of drug in every 5 mL of liquid |
| 10 mg/mL | 10 mg of drug in every 1 mL of liquid |
| 1 mg/mL | 1 mg of drug in every 1 mL of liquid |
The Stock Ratio
The label concentration is your stock ratio. Always write it as a fraction before setting up your calculation:
250 mg/5 mL becomes \(\frac{5 \text{ mL}}{250 \text{ mg}}\)
Note the mL goes in the numerator because mL is what you want in your answer.
Basic Liquid Calculation¶
Example 1: Order: amoxicillin 250 mg orally Stock: 125 mg/5 mL
Example 2: Order: ibuprofen 400 mg orally Stock: 200 mg/5 mL
Example 3: Order: morphine 15 mg orally Stock: 10 mg/mL oral solution
Unit Conversion Required¶
Example 4: Order: amoxicillin 0.5 g orally Stock: 250 mg/5 mL
Example 5: Order: clarithromycin 0.375 g orally Stock: 125 mg/5 mL
Measuring Liquid Medications¶
Always Use a Calibrated Device
Never use a kitchen spoon to measure liquid medications. Always use one of the following:
- Oral syringe — most accurate, especially for small volumes under 5 mL
- Medicine cup — suitable for volumes 5 mL and above
- Dosing spoon — calibrated, acceptable for home use
Read the measurement at eye level at the bottom of the meniscus (the curved surface of the liquid).
Reconstitution¶
Some liquid medications come as a powder that must be mixed with water before use.
Reconstitution
When reconstituting a powder:
- Read the label for the exact amount of water to add
- Add the specified volume of water — not more, not less
- Shake or mix as directed
- Check the resulting concentration on the label
- Note the expiry date after reconstitution
- Label with date and time of reconstitution
The concentration printed on the label only applies after reconstitution with the specified volume.
Reasonableness Check¶
Liquid Dose Safety Guidelines
- Oral liquid doses are typically between 5 mL and 30 mL
- Doses under 1 mL orally are unusual — recheck
- Doses over 30 mL orally are unusual — recheck
- Injectable liquid doses are typically 0.5 mL to 3 mL
Practice Problems¶
Problem 1
Order: cetirizine 10 mg orally Stock: 5 mg/5 mL syrup How many mL?
Answer
Problem 2
Order: paracetamol 500 mg orally Stock: 250 mg/5 mL suspension How many mL?
Answer
Problem 3
Order: morphine 7.5 mg orally Stock: 10 mg/5 mL solution How many mL?
Answer
Round to nearest tenth: 3.8 mL
Problem 4
Order: amoxicillin 0.75 g orally Stock: 250 mg/5 mL How many mL?
Answer
Problem 5
Order: ibuprofen 0.6 g orally Stock: 200 mg/5 mL How many mL?
Answer
Problem 6
Order: prednisolone 30 mg orally Stock: 15 mg/5 mL solution How many mL?
Answer
Problem 7 — Flag This Answer
Order: digoxin 0.5 mg orally Stock: 0.05 mg/mL solution How many mL?
Answer
Verify Before Administering
10 mL of digoxin is at the upper limit of reasonable. Digoxin is a high alert medication. Independently verify the order, stock concentration, and your calculation with a second nurse before administering.
Clinical Tip
When drawing up liquid medications in an oral syringe, always expel any air bubbles and confirm the volume at eye level before administering. A small air bubble can make a 5 mL dose appear to be 6 mL.