Pharmacology
Animal Weight-Based Dose Calculator
Scales a human reference dose down to a laboratory animal by body weight, and works out the syringe volume from the stock concentration.
Target animal dose
0.1786mg
178.57 µg · normalised 7.143 mg/kg
Linear scaling, not allometric
Drug & adult reference
The human dose the animal dose is scaled from.
Recorded on the protocol only.
The usual human dose.
Conventionally a 70 kg adult.
Animal model
Species sets the default body weight and the injection volume limit.
Max injection volume 0.2 mL
Weigh the animal on the day.
Calculates the exact volume to draw into the syringe.
Working
The practical notebook steps.
Species reference
Default weights and the injection volumes usually accepted.
| Species | Typical weight | Max injection volume |
|---|---|---|
| Mouse | 25 g | 0.2 mL |
| Rat | 200 g | 1 mL |
| Guinea Pig | 400 g | 1.5 mL |
| Rabbit | 2000 g | 3 mL |
Everything is converted to milligrams and grams first, then scaled in two steps:
dose per gram = adult dose (mg) / adult weight (g)
animal dose (mg) = dose per gram × animal weight (g)
The syringe volume follows from the stock concentration:
volume (mL) = animal dose (mg) / stock concentration (mg/mL)
Weight conversions are 1 kg = 1000 g and 1 lb = 453.59237 g; dose conversions are 1 g = 1000 mg and 1 mcg = 0.001 mg. Because the scaling is linear, the normalised mg/kg figure always equals the adult mg/kg — that is a property of the method, not a bug.
Keep learning
References
- Stockton SJ. Stoklosa and Ansel's Pharmaceutical Calculations. 16th ed. Philadelphia: Wolters Kluwer; 2021.
Common questions
Because this is linear weight scaling. Metabolic rate scales with roughly the ¾ power of body mass, not with mass itself, so a mouse clears a drug far faster per kilogram than a human. Converting by body surface area with Km factors (human 37, mouse 3) gives a mouse dose about 12× higher in mg/kg.
Human equivalent dose (mg/kg) = animal dose (mg/kg) × (animal Km / human Km). Running it the other way, animal dose = human mg/kg × (37 / animal Km): 37/6 ≈ 6.2× for a rat, 37/3 ≈ 12.3× for a mouse.
Raise the stock concentration so the same dose fits a smaller volume, or split the dose between injection sites if the protocol allows. The limits shown are conservative typical values — the accepted volume also depends on the route (IP tolerates more than IV or SC).
Because linear scaling keeps the dose proportional to weight, so every animal receives the same mg/kg as the adult reference. It is shown so the number can be compared against literature mg/kg doses — where you will usually see the discrepancy described above.
Prepared by the PharmaWallah student team. Verify results with your textbook or instructor. Report an error · Editorial policy