How should an injection be given to a rat? - briefly
Use a sterile 27–30 G needle to deliver the dose subcutaneously or intraperitoneally after gentle restraint and site disinfection. Limit the volume to ≤0.1 ml per 10 g body weight to prevent tissue injury.
How should an injection be given to a rat? - in detail
Administering an injection to a laboratory rat requires strict adherence to aseptic technique, accurate dosage calculation, and appropriate restraint.
Equipment
- 1‑ml syringe with a 27–30 G needle for subcutaneous or intraperitoneal routes; 25–27 G needle for intramuscular or intravenous delivery.
- Sterile gloves, alcohol swabs, and a disinfected injection surface.
- Calibrated balance for weighing the animal and a formula for converting dose (mg kg⁻¹) to volume (µL).
Preparation
- Weigh the rat and record the mass to the nearest gram.
- Compute the required volume using the concentration of the drug solution.
- Draw the calculated volume into the syringe, expelling air bubbles.
- Label the syringe with drug name, concentration, and dose.
Restraint
- Place the rat on a padded surface.
- Secure the animal by gently holding the scruff of the neck with one hand while supporting the torso with the other.
- Avoid excessive pressure that could cause injury or stress.
Injection sites and technique
Subcutaneous (SC)
- Locate a loose area of skin on the dorsal neck or flank.
- Pinch the skin fold to create a tent.
- Insert the needle bevel up at a 45° angle, advance 2–3 mm, and inject the solution steadily.
- Release the skin fold and observe for a small bleb indicating correct placement.
Intraperitoneal (IP)
- Identify the lower right quadrant of the abdomen, avoiding the midline.
- Insert the needle bevel down at a 20–30° angle, penetrating the peritoneal cavity 5–7 mm.
- Deliver the dose slowly to prevent reflux.
Intramuscular (IM)
- Target the quadriceps femoris on the hind limb.
- Position the needle perpendicular to the muscle surface, inserting 5–6 mm.
- Depress the plunger gently until the full volume is administered.
Intravenous (IV) – tail vein
- Warm the tail with a heat lamp for 1–2 minutes to dilate vessels.
- Apply a small amount of alcohol to the tail surface.
- Insert the needle bevel up at a shallow angle, visualizing entry into the vein.
- Confirm blood return before delivering the drug.
Post‑injection care
- Observe the rat for at least 10 minutes for signs of distress, bleeding, or abnormal behavior.
- Return the animal to its cage, providing fresh bedding and water.
- Document the procedure, including site, volume, needle gauge, and any adverse observations.
Following these steps ensures accurate delivery, minimizes discomfort, and maintains experimental integrity.