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Administration by Injection

The injection of substances directly into the body requires strict asepsis to avoid complications. Injected substances and the needles/syringes used to inject substances must be sterile. Potential complications for all routes of injection include infection, local irritation, pain and damage to surrounding tissue. Video demonstrations of various injection routes are available on the Procedures With Care website. A video demonstration of the retro-orbital injection route is available on the ARP website. Listed below are recommended maximum injection volumes for specific injection routes. Factors to be considered when selecting an injection route include:

  • Pharmacology of the substance administered
  • Species of animal used
  • Final effect desired (e.g., local or systemic)
  • Minimization of stress and discomfort to the animal

Injection Routes


Potential complications:

  • Inadvertent injection into various abdominal organs and subcutaneous, retroperitoneal or intramuscular spaces
  • Chemical peritonitis due to irritating substances
  • Fibrous tissue adhesions within the abdominal cavity
  • Perforation and/or bleeding of an abdominal organ
  • Respiratory distress or discomfort if the volume administered is too large
  • With repeated administration, a cumulative irritant effect and needle induced damage

Maximum volumes for intraperitoneal injection:

  • Mouse and Rat = 10 ml/kg body weight


Potential complications:

  • Bacteremia/septicemia
  • Extravascular delivery of substance administered leading to local soft tissue damage, infection, pain and/or tissue death
  • Vascular occlusion, emboli and thrombosis if substances containing particulate material or low pH precipitate in the bloodstream
  • Hemolysis, coagulation or anaphylaxis depending on the substance injected

Maximum volumes for intravenous injection:

  • Mouse: Tail vein and retro-orbital [maximum volume (bolus) = 5 ml/kg]
  • Rat: Maximum volume (bolus) = 5 ml/kg


Potential complications:

  • Pain
  • Muscle damage and/or death of tissue
  • Irritation or damage to nearby nerves
  • Generally not useful in small rodents due to small volume that can be safely administered without tissue damage

Maximum volumes for intramuscular injection:

  • Mouse and Rat = 0.05 ml/kg/site; maximum of 2-4 sites


Potential complications:

  • Aspiration pneumonia
  • Suffocation
  • Inaccurate dosing due to sneezing (deep sedation or light anesthesia may decrease this)

Maximum volumes for intranasal administration:

  • Mouse and rat = 35 (minimum) to 50 microliters (maximum)


Non-irritating substances can be administered subcutaneously in almost any area of the body where the skin overlying the site is loose enough to allow for volume expansion. Typical sites include the flanks and dorsal shoulder regions.

Maximum volumes for subcutaneous administration:

  • Mouse = 10 ml/kg total, divided between 2-3 sites
  • Rat = 5-10 ml/kg total, divided between 2-4 sites



Fox JG, Barthold SW, Davisson MT, Newcomer CE, Quimby FW, Smith AL. The Mouse in Biomedical Research (2nd ed.). 2007. New York, NY: Elsevier Academic Press.

Suckow MA, Weisbroth SH, Franklin CL (Eds.). The Laboratory Rat (2nd ed.). 2006. New York, NY: Elsevier Academic Press.

Turner PV, Brabb T, Pekow C, Vasbinder MA. Administration of Substances to Laboratory Animals: Routes of Administration and Factors to Consider. 2011. JAALAS 50 (5): 600-613.