Where should a subcutaneous injection be given to a rat? - briefly
Inject into the loose skin over the dorsal midline, typically between the scapulae, ensuring the area is free of fur and avoiding the tail and hindlimb joints. This site provides ample subcutaneous space for safe administration.
Where should a subcutaneous injection be given to a rat? - in detail
The most reliable site for delivering a subcutaneous dose in a laboratory rat is the loose skin over the dorsal cervical region, commonly referred to as the scruff. This area provides ample subcutaneous space, minimal muscle interference, and easy access for restraining the animal.
Key considerations for the injection:
- Animal positioning – hold the rat gently but securely, allowing the neck skin to be lifted away from underlying tissue.
- Needle selection – use a 25‑27 G needle, ½ inch in length for volumes up to 1 ml; larger volumes may require a longer needle to avoid penetration of the muscle layer.
- Injection angle – insert the needle at a 30‑45° angle relative to the skin surface to ensure entry into the subcutaneous space without entering the muscle.
- Volume limits – do not exceed 0.2 ml per 100 g body weight; larger volumes increase the risk of tissue disruption and absorption variability.
- Site rotation – alternate injection sites on the dorsal neck or flank to prevent localized irritation and fibrosis.
Technique steps:
- Restrain the rat and locate the dorsal cervical skin fold.
- Pinch the skin fold gently to create a tent.
- Insert the needle bevel‑up at the prescribed angle.
- Depress the plunger smoothly, delivering the full dose.
- Withdraw the needle and release the skin fold, monitoring the animal for brief post‑injection observation.
Alternative sites, such as the lateral flank or the inguinal region, are acceptable when the dorsal neck is compromised, but they require careful assessment of skin laxity and avoidance of underlying muscle. Consistent site selection, proper needle gauge, and adherence to volume guidelines ensure reliable drug absorption and minimize animal distress.