December 2025
In this VETgirl online veterinary continuing education blog, Amanda M. Shelby, RVT, VTS (Anesthesia & Analgesia) describes how to calculate dilutions from percent solutions. Veterinary technicians are responsible for completing patient prescriptions, which require performing clinical mathematics correctly and sometimes quickly. Percent solutions can be confusing. Let’s work through a couple of clinical examples to best explain how to perform dilutions from percent solutions correctly!

Calculating Dilutions from Percent Solutions Confidently

By Amanda M. Shelby, RVT, VTS (Anesthesia & Analgesia), VETgirl Senior CE Specialist

Before we get started, let’s review two foundational concepts:

Dilutions equation:

So, what is this formula mean? Here, the concentration (C1) multiplied by the volume (V1) of that solution will equal the concentration (C2) multiplied by the volume (V2) of the desired solution. The units for C1 and C2, as well as V1 and V2, must be the same on either side of the equal side. This means if C1 is mg/mL, then C2 will be mg/mL. Similarly, if you are working with percentage (%) concentrations for C1, then C2 will need to be a percent. The same is true for V1 and V2 – if V1 is milliliters (mL), solving for V2, the answer will be in mL. Most commonly, we are solving this equation for a volume.

Conversion factor for percent solutions:

Percents are used to describe solution concentrations (e.g., lidocaine, mannitol). Determining a volume to administer requires converting the concentration from a percent to weight of solute per volume (i.e. mg/mL). Below is the math explaining the conversion of a 2% lidocaine solution to mg/mL (see Example 1):

Example 1

That is, a 2% solution is representative of 2 g of solute per 100 mL of diluent. From there, convert to g/mL to mg/mL if preferred.

Case 1. Sampson

Photo courtesy of Amanda M. Shelby.

Sampson, a 7.5-kg, 2-year-old, male neutered, domestic short hair (DSH) cat presents with the primary complaint of straining to urinate. A firm bladder (which Sampson reacts to painfully during palpation) and a quick ultrasound of his caudal abdomen demonstrates a full, distended bladder. Sampson is diagnosed with a feline urinary obstruction (UO). The attending veterinarian’s orders include initial stabilization including placement of an intravenous (IV) catheter, chemistry blood work, and starting fluids. Sampson’s serum chemistry shows a hyperkalemia (e.g., elevated potassium) of 7.5 mEq/L (reference range 3.5-5.5 mEq/L) and a hypoglycemia (e.g., low blood sugar) at 54 mg/dL (reference range 80-120 mg/dL). His overseeing veterinarian prescribes administration of a 50% dextrose bolus (1 mL/kg, IV over 2-3 minutes) followed by a 5% dextrose fluid additive in his 500 mL bag of LRS.

The Prescription:

To set up the equation for Sampson, see example 2:

Example 2

Creating the diluted solution:

  1. 500 mL is the total volume of the prescribed dextrose solution. Remove 50 mL from the 500 mL LRS bag.
  2. Using aseptic technique, add 50 mL of the 50% stock dextrose solution to the LRS bag to make a total volume of 500 mL (450 mL LRS + 50 mL of 50% dextrose)
  3. Label the LRS fluid bag appropriately to mark it with its additives. Suggested labeling to include: 50 mL of 50% dextrose added to 450 mL of LRS to make a total volume of 500 mL of 5% dextrose solution in LRS. Consider adding the date and initials of the person for accountability.

Note: When adding dextrose to IV fluids, this is most commonly done at 2.5-5% dextrose supplementation. Please note that concentrations > 5% typically have to administered through a central jugular vein to prevent phlebitis. Also note that dextrose supplementation as a CRI in IV fluids typically is not based on kilogram weight.

Case 2: Freddy

Photo courtesy of Amanda M. Shelby.

Freddy, a 10-kg, 5-year-old, neutered mixed-breed dog, presented with a wound on the right thorax. The attending veterinarian prescribed a sedated ‘clip and clean’ procedure of the wound, requesting that the wound be flushed with 1 L of 0.05% solution of chlorhexidine in sterile 0.9% saline before they further debride and bandage the wound. The hospital has a 2% chlorhexidine solution in stock. As the veterinary technician, you need to determine the volume of the 2% chlorhexidine stock solution to add to make a 0.05% chlorhexidine solution in a 1L bag of 0.9% saline.

The Prescription:

To set up the equation see example 3:

Example 3

 

Creating the diluted solution:

  1. First, remove 25 mL from the 1000 mL bag of 0.9% saline.
  2. Using aseptic technique, add 25 mL of the 2% chlorhexidine solution to make a total volume of 1000 mL of 0.05% chlorhexidine solution in 0.9% saline.
  3. Label the bag appropriately with the additive, concentration, date, and initials.

Case 3. Dolly

Photo courtesy of Amanda M. Shelby.

Dolly, a two-year-old, 3.6 kg, female spayed DSH, presented with severe anisocoria (e.g., uneven pupil sizes) and a suspected, unknown cause of increased intracranial pressure. The veterinarian prescribes administration of a 1 g/kg mannitol IV bolus over 20-30 minutes. The clinic has 20% stock mannitol solution on the shelf. As the veterinary technician, you need to calculate how many mL of the 20% mannitol solution is required for this patient.

The Prescription:

To perform the conversion and dose calculation for Dolly, see example 4:

Example 4

 

Note: In general, administering this large volume (18 mL) to a cat feels innately wrong (because it should feel like a very large volume!). With mannitol, this larger volume is common based on the concentration/osmolality of the drug… but always double check if the volume feels “too big”!

We hope you found this case-based review on how to perform dilutions and conversions of percent solutions to mg/mL or g/mL helpful! Confidence in mathematics is built by repetition. There is no shame in having math double-checked by a peer to ensure patients receive the correct doses of prescribed medications! When in doubt, you always want to double check doses to be safe and avoid medical errors!

Don’t like math or in a hurry…check out our dextrose calculation wheel HERE!

 

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