When performing an intraperitoneal injection in mice, where is the injection typically placed and what should be avoided?

• A. Lower right quadrant to avoid puncturing the cecum or bladder.
• B. Upper left quadrant to avoid liver.
• C. Midline upper abdomen to avoid stomach.
• D. Lower left quadrant to avoid spleen.

Answer: (A)

In mice, intraperitoneal injections are placed in a spot that minimizes the chance of hitting major organs. The lower right quadrant is chosen because the cecum sits on the right side of the abdomen and the bladder lies toward the ventral midline. Targeting this area reduces the risk of puncturing either structure and causing leakage or injury. The other regions contain organs that are more likely to be damaged if punctured—stomach and liver in the upper abdomen, spleen on the left side—so they are less ideal for this route. Keeping the needle in the lower right quadrant provides the safest access to the peritoneal cavity.