- First locate the point of entry for the needle.
- Draw an imaginary line across the abdomen just above the knees (see image above).
- The needle will be inserted along this line on the animal’s right side and close to the midline.
- As this is a female, you can see that the point of entry is cranial to and slightly medial of the last nipple.
- Inserting the needle on the mouse’s right side avoids the cecum, which is a large fluid-filled organ on the left side of the abdomen. The small intestines (on the right side) are less likely to be punctured by the needle.
- Inserting the needle too far caudally or laterally from the insertion point shown above would risk making an injection into the rear leg which would injure the muscle tissue.
- To perform an IP injection, the mouse must be well restrained so that it cannot move during the procedure. This avoids traumatizing the organs once the needle has entered the abdomen.
- Restrain the mouse and tilt so that the head is facing downward and its abdoment is exposed.
- Insert the needle into the abdomen at about a 30-degree angle after disinfecting injection site..
- The shaft of the needle should enter to a depth of about half a centimeter.
- Aspirate to be sure that the needle has not penetrated a blood vessel, the intestines, or the urinary bladder.
- Greenish brown aspirate indicates needle penetration into intestines.
- Yellow aspirate indicates needle penetration into the bladder
- If any fluid is aspirated, your solution is contaminated and must be discarded and the procedure repeated with a new syringe and needle.
- If no fluid is aspirated, you may inject.
- Withdraw the needle and return the mouse to its cage.
The recommended needle size for IP injections in the mouse is 25-27 gauge.
Procedure same as in the mouse. The recommended needle size for IP injections in the rat is 25 gauge.
Information from AALAS learning Library