When determining IP injection volume for a mouse, which factor is most important?

• A. Eye color
• B. Body weight and health status
• C. Time of day
• D. Diet type

Answer: (B)

When giving intraperitoneal injections in a mouse, the most important consideration is how much volume the animal can safely receive based on its size and condition. Dosing is scaled to body weight because a small mouse has a much smaller peritoneal cavity and different circulation compared to a larger one, so the same absolute amount can cause overdistension, discomfort, or even injury if not adjusted. Health status matters because an ill, dehydrated, or compromised mouse may tolerate a smaller volume or require a different route of administration to minimize stress and adverse effects.

To apply this in practice, you weigh the mouse and calculate the injection volume from a weight-based guideline, then assess overall health and hydration. A well-hydrated, healthy mouse will tolerate the standard weight-based volume, while a lighter or unwell mouse may need a reduced volume. Factors like eye color, time of day, or diet type do not determine how much volume can be safely injected and should not drive the decision.

So, the key idea is that volume is driven by body weight and health status because these directly affect safe capacity and tolerability of the injection.