Liquid Medications¶
Liquid medications are used when patients cannot swallow tablets or capsules, for pediatric patients, and for medications only available in liquid form. The calculation method is the same as tablets — unit cancellation — but the answer is a volume in 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 |
Orienting the stock ratio
The label concentration is your stock ratio. Write it as a fraction with mL on top — that way mL cancels in and your answer comes out in mL:
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 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. See Reconstitution for the full two-step process: establishing the concentration from the label, then calculating the draw volume.
Reasonableness Check¶
Liquid dose safety guidelines
- Oral liquid doses are typically 5–30 mL per dose
- Doses under 1 mL orally are unusual — recheck
- Doses over 30 mL orally are unusual — recheck
- Injectable liquid doses are typically 0.5–3 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.
Syringe accuracy
When drawing up liquid medications in an oral syringe, 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.