4.5.1 Routes of Administration

The oral (per os) route, administered by gavage using a graduated feeding needle, permits a maximum volume of approximately 10 mL/kg in the rat; correct...

The oral (per os) route, administered by gavage using a graduated feeding needle, permits a maximum volume of approximately 10 mL/kg in the rat; correct needle placement must be confirmed before dosing, and animals are conventionally fasted for 12–16 hours beforehand to standardise gastric emptying. The intraperitoneal (i.p.) route, also limited to approximately 10 mL/kg and delivered via a 27-gauge needle into the lower left abdominal quadrant to avoid the bladder and gastrointestinal tract, is the most common parenteral route in mice owing to its technical simplicity. The intravenous (i.v.) route, limited to approximately 5 mL/kg administered slowly, uses the tail vein in rats and mice or the marginal ear vein in rabbits, with gentle warming of the limb used to promote vasodilation and ease of injection. The subcutaneous (s.c.) route, also limited to approximately 5 mL/kg, is typically administered into the scruff of the neck and produces a depot effect suited to chronic dosing regimens. The intramuscular (i.m.) route is limited to approximately 0.5 mL per injection site in the thigh muscle; because it is comparatively painful, its use is generally limited to vaccine and adjuvant studies. Topical and transdermal administration requires shaving the application area, defining it precisely in square centimetres, and may be studied ex-vivo using Franz diffusion cells, with tape-stripping used to assess stratum corneum penetration. The intranasal route, delivering 5–10 microlitres per nostril to an anaesthetised animal with the head tilted back, is used for both CNS-targeted delivery and vaccine studies.