Handling & dosing
An injection into the peritoneal cavity in the lower right quadrant, with the animal tilted head down. Fast and simple, but a small proportion of injections land in gut, bladder or fat even in skilled hands.
Our ruleSimulations prepare you for the bench but don't replace hands-on practice.
Intraperitoneal
An injection into the peritoneal cavity in the lower right quadrant, with the animal tilted head down. Fast and simple, but a small proportion of injections land in gut, bladder or fat even in skilled hands.
How it differs from the standard method
- Mouse good practice up to about 20 mL/kg (10 mL/kg is a common local limit).
- Absorbed largely through the portal circulation, so first-pass metabolism in the liver applies.
- 25–27 G needle for a mouse.
1Giving a known dose to a living animal
A dose is written in milligrams per kilogram, so every animal gets a volume worked out from its own weight on the day. The route then decides how much of that dose reaches the circulation and how fast: all of it at once intravenously, most of it within minutes intraperitoneally, more slowly from under the skin, and often only a fraction by mouth. Choosing a route is choosing an exposure, a speed, and a set of things that can go wrong.
Intraperitoneal
Into the abdominal cavity, lower right quadrant. Fast absorption; a misplaced needle doses the gut or bladder instead.
Intravenous
Usually a lateral tail vein in rodents. Complete, immediate exposure; a miss deposits the dose in the tissue.
Oral gavage
A tube into the stomach. Mimics oral drugs; the main risks are oesophageal injury and dosing the airway.
Subcutaneous
Under loose skin over the shoulders or flank. Slow, steady absorption; the easiest route to do well.
2Volume limits, vehicles and the animal's experience
Every route has a volume limit per kilogram, because tissue can only take so much fluid comfortably: commonly cited good-practice values for a mouse are about 10 mL/kg by gavage or under the skin, 20 mL/kg intraperitoneally and 5 mL/kg as an intravenous bolus, and your approved protocol may be stricter. The vehicle must be tolerated on its own, sterile for any injection, and close to neutral pH and isotonic.
3Humane endpoints and the 3Rs
Every dosing study runs against a score sheet agreed in advance: body weight and clinical signs scored daily, and a humane endpoint, often around 20% weight loss or a set clinical score, at which an animal is killed humanely rather than left to deteriorate. A pilot study sets the maximum tolerated dose, the main study uses the lowest dose that answers the question, and vehicle controls, randomisation and blinding make sure the animals used give an interpretable result: replacement, reduction and refinement in practice.
Key terms
Practise these as flashcards →Dose per kilogram of body weight; the volume follows from the animal's weight and the solution's concentration.
Volume per kilogram of body weight, the unit route limits are written in; numerically the same as µL/g.
The fraction of a dose that reaches the systemic circulation; 100% intravenously, often much less by mouth.
Animals given the vehicle alone by the same route and handling, so the procedure's own effects can be separated from the compound's.
The highest dose that does not cause unacceptable toxicity, set in a small pilot study.
A pre-agreed point (weight loss, clinical score) at which an animal is killed humanely to prevent further suffering.
Replacement, reduction and refinement: the framework for humane animal research.
Moving mice with a tube or cupped hands instead of by the tail, which reduces anxiety.
When to use it
- Testing a compound's pharmacokinetics, efficacy or toxicity where a cell or tissue model cannot answer the question.
- Giving an agent that a model depends on, such as a tamoxifen-inducible deletion or a labelling substrate before imaging.
- Delivering an anaesthetic or analgesic as part of a surgical or imaging procedure.
Compared with alternatives
Sampling blood after dosing is how plasma levels are measured; its volume limits are set by circulating blood volume.
Dosing is usually one part of a longer model, where treatment is given to animals carrying a tumour, wound or implant.
Where the question is about a tissue's own response rather than whole-body exposure, an organoid model can replace animals altogether.
Sub-techniques
Choosing one here switches the whole page, including the protocol and the lab, to it.
An injection into the peritoneal cavity in the lower right quadrant, with the animal tilted head down. Fast and simple, but a small proportion of injections land in gut, bladder or fat even in skilled hands.
- Mouse good practice up to about 20 mL/kg (10 mL/kg is a common local limit).
- Absorbed largely through the portal circulation, so first-pass metabolism in the liver applies.
- 25–27 G needle for a mouse.