Administration of Drugs and Experimental Compounds in Mice and Rats


Administration of compounds plays a large part in experimental design using animals.  This policy addresses issues related to administration of compounds within a protocol with the goal of facilitating the procedure for the person administering the compound as well as minimizing discomfort and supporting well-being of the animal.  Over 90% of animals used in research are rats and mice, and this policy deals only with rats and mice.

“The use of pharmaceutical-grade chemicals and other substances ensures that toxic or unwanted side effects are not introduced into studies conducted in experimental animals.  They should therefore be used, when available, for all animal-related procedures.”1

“Before administering any substance (therapeutic or experimental) to an animal subject, one must consider the pH, sterility, and chemical nature (odor, taste, mucosal irritability, osmolarity, solubility, light sensitivity, and hazard status) of the compound and make appropriate decisions on the dose to be administered, frequency of administration, volume to be administered, the  solvent (if necessary), and route of administration.” 2

This policy addresses these issues plus requirements for observation and care of the animal during and after administration.


A.  Any compound to be administered must be reviewed and approved by the IACUC.

Compounds that are administered on an emergency basis as part of veterinary care do not require prior IACUC approval.  These may include fluids, anesthetics, analgesics, antibiotics or other pharmaceutical compounds.

B.  Parameters to be defined in the IACUC protocol include:

Specific info for mice and rats can be found in Tables 1 and 2 and indicated links at

  1. Name of compound or a brief chemical description if not generally known unless proprietary.
  2. Dose (mg/kg) of compound.
  3. Route of administration
  4. Volume of administration.  See Tables 1 and 2 for recommended needle sizes and volumes.
  5. Frequency of administration, and intervals between repeat administration for example “once”, once daily for 6 weeks” or “continuously for two weeks via osmotic pump”.
  6. Information on solvent/vehicle including pH and other chemical characteristics.
  7. Effects of compound and/or vehicle including intended effects and side effects.
  8. The use of any non-pharmaceutical grade chemical or compound must be described and justified in the IACUC protocol.

C.  Following administration of compound the animal must be monitored and findings documented and available in the animal room.  A form for documenting monitoring and animal response is available at

Frequency of monitoring depends upon the study and is determined by the Principal Investigator (PI) and the IACUC and is specified in the approved protocol.

D. Experimental compounds added to the animal’s food or water must be clearly labeled.

Coming soon: IACUC Policy on Additives to Drinking Water

E.   Investigators and research staff must be trained in the method(s) of adminstration used.


Routes of administration are designated as ENTERAL or PARENTERAL

A.  ENTERAL or per os routes of administration

  1. Additives to the drinking water: When additives are placed in the drinking water it is the responsibility of the investigator to monitor the animal(s) and assure that adequate fluid intake occurs.  See:  IACUC Policy Additives to Drinking Water
  2. Additives to the food: When additives are placed in the food it is the responsibility of the investigator to monitor the animal(s) and assure that adequate food intake occurs.
  3. Intragastric via gavage: The investigator must be trained and experienced in this procedure prior to undertaking it.  This route of administration is most ensured to deliver an exact per os dose.                               
  4. Rectal administration2  is enteral (to the GI tract) but not per os.  Rectal installation of drug solution can be performed using a small-gauge soft, flexible tubing (3.5 French red rubber feeding tube).  The edges of the tubing should be smooth/rounded.  Attach dosing syringe to end of tubing, making sure to eliminate all air bubbles.  Limit the injection volume to 0.5 ml in the mouse and 1-2 ml in the rat.2

B.  PARENTERAL routes of administration

The route chosen for administration will depend upon the species, volume and material to be injected and desired rate of absorption.

The investigator should know the physiological properties of the substance to be injected (see Section E) because tissue damage and discomfort can be caused by irritating vehicles or drugs.  Accurate placement of the needle should always be determined prior to the actual injection by applying slight negative pressure on the syringe and observing the flashback of blood or other body fluid. 3

For specific administration volumes and needle gauges see Tables 1 and 2.

For detailed instructions see

  1. Subcutaneous (SC) injections:  Manually restrain the animal.  The best place to inject is into the loose skin on the back of the neck.  A mouse may easily be injected by one person, whereas a rat may require restraint by one person and injection by the other.  Anesthesia is generally not required.
  2. Subcutaneous slow release formulations: If repeated or long-term SC dosing is required, and the formulation is suitable for this, slow release pellets or Silastic capsules may be implanted.
  3. Intraperitoneal (IP): Commonly used in rats and mice IP administration results in a faster absorption into the vasculature than SC administration and is thus akin to IV administration.  Any irritating compound, such as ketamine or pentobarbital, is less irritating if administered IP.   A mouse may easily be injected by one person, whereas a rat may require restraint by one person and injection by the other.  Anesthesia is generally not required.
  4. Intravascular: Intravenous (IV) & Intraarterial (IA). Intravenous administration is the commonly used route.   Intraarterial administration is discouraged and must be scientifically justified and approved in the IACUC protocol.
    • Tail vein injections are commonly performed in mice and rats and uses the lateral tail vein located on either side of the tail.  Anesthesia is generally not required for this procedure..  The maximum volume for bolus injections is 5 ml/kg.  For continuous administration the maximum IV volume is 4 ml/kg/hour.4
    • Other sites for IV administration in rats is the jugular vein.  This requires anesthesia and aseptic preparation of the site.   Finally, continuous IV or intraarterial administration may be achieved via an osmotic pump.  See IACUC Policy for Osmotic Pumps.
    • If an irritating compound designed for IV administration, for example pentobarbital, should extravasate (be accidentally injected outside the vein) it is recommended that to avoid tissue necrosis it be diluted in the surrounding tissues by administration of sterile 0.9% saline.
  5. Retro-orbital injections in mice discouraged and must be justified:  The retro-orbital route of administration5 into the retro-orbital sinus may be used in mice.  Anesthesia is required for this procedure.  This route may be used as an alternative to tail vein administration and is acceptable provided that the operator is trained and proficient in this technique.  Cell suspensions should be filtered or agitated prior to injection to prevent cell clumping.  Caution is advised when administrating cell lines via this route due to the possibility of cells escaping into the surrounding tissues and introducing a retroorbital tumor mass.
  6. Intramuscular (IM): Not recommended  in mice due to their small muscle mass.  If scientifically justified, and it must be done in rats, < 0.2 ml/site may be injected into the quadriceps or the gluteal muscles, which are the largest.  If injecting into the gluteals make sure to avoid the sciatic nerve that runs along the caudal aspect of the femur.
  7. Topical: BU policy is to keep areas of skin injury or treatment to 10-20% of the total body surface of the animal and it must not exceed 25 % of total body surface. The body surface of a 20 g mouse is 36 cm2 and of a 25 g mouse 42 cm2. The % surface area to be treated must be previously discussed with and approved by the veterinarian.  If the skin is to be pre-treated prior to application of the test compound, such as with use of Nair or waxing, this treatment must be performed by a trained and qualified person and the pretreated  area must not exceed 25% of total body surface.
  8. After the topical treatment is applied the animals must be singly housed in order to prevent the animals from licking the compound off each other.
  9. Intradermal  (ID): Approved only if scientifically justified in the IACUC protocol.  Used primarily for studies in                             inflammation and immunologic studies.  See IACUC Policy for Adjuvants                                    
  10. Ocular: Only compounds designated for and approved for ocular administration.
  11. Upper Respiratory Tract-Intranasal: May require anesthesia.  Maximum volume to be injected in adult mice may be as much as 62 µl but it is recommended that the volume is kept to 30 µl per nostril. 6
  12. Upper Respiratory Tract-Intratracheal: Maximum volume to be injected in adult mice is 50 µl.  This method, requiring anesthesia, must be described in detail in the IACUC protocol.  Variations on this procedure may be acceptable. In general, after being anesthetized with isoflurane, the mouse is placed in an almost vertical position, head up, the tongue is retracted and the infusate placed in the mouth.  Once the tongue is retracted, the liquid is aspirated and cannot be swallowed.
  13. Intracranial: This method, requiring anesthesia and stereotactic surgery for placement of the cannula and used in pharmacology and neuroscience studies, must be described in detail in the IACUC protocol.  The administration may be either via bolus or continuous administration.
    • Via a surgically implanted cerebral cannula
    • Via direct injection
    • Via osmotic pump catheter  See IACUC Policy for Osmotic Pumps
  14. Intrathoracic administration: Any compound administered percutaneously into the chest requires animal to be placed under anesthesia.  This specialized procedure must be described in detail in the IACUC protocol.
  15. Intracardiac administration: Any compound administered percutaneously or directly via an open chest into the heart requires animal to be placed under general anesthesia.  This specialized procedure must be described in detail in the IACUC protocol.
  16. Osmotic pumps: Used for continuous administration including SC, IP, IV and IA or to specific organs.  The placement of an osmotic pump is encouraged whenever administration of a compound must continue for several days or weeks.  See IACUC Policy for Osmotic Pumps 

C.  Needles

  1. The higher the number (gauge) the smaller the needle.
  2. Always use the smallest needle (highest gauge) that will do the job.  For recommended needle sizes See Tables 1 and 2.
  3. Sterile needles and syringes are necessary to administer a sterile solution.   Do not reuse needles.
  4. DO NOT RECAP needles.
  5. Dispose of used needles and syringes in a designated sharps container.

D.  Frequency of administration and Intervals between administration

  1. Limit frequency of administration as much as possible consistent with the medical or experimental  requirements.
  2. Avoid more then once a day administration if possible.  Please note that this is not possible with many analgesics and antibiotics which have a limited duration of action.
  3. For repeat administrations of experimental compounds consider implantation of osmotic pump.

E.   Characteristics of compound and solvent (vehicle)

  1. pH: Know the pH of the compound AND the vehicle.  Aim for pH ~7.  If the pH is higher or lower try one of the following:
    1. Buffer to pH 7 if possible
    2. Dilute the solution using sterile normal saline or PBS
    3. Do not inject a high or low pH preparation IM or SC as this will be painful and cause tissue       necrosis.  Recommended alternate routes of administration is IP or IV.
    4. Examples:
      1. Pentobarbital is a very basic pH (~11).  Only administer IV or IP; never IM or SC.
      2. Ketamine has an acidic pH (~4).  In rodents ketamine is always administered IP.  IM       administration can cause tissue necrosis.
  2. Sterility: The compound and solvent must be rendered sterile either by sterilization or filtration.  Only Pharmaceutical-Grade compounds can be administered into animals.  Investigators are expected to use pharmaceutical grade medications whenever they are available, even in acute procedures.1
  3. Odor: An offensive odor would limit voluntary intake of any compound.
  4. Taste: Some compounds administered in the drinking water have a bitter taste and are better accepted if sucrose is added.  These include but are not limited to tetracycline, doxycycline and metronidazole.  Adding 2.0-5.0 g sucrose/100 ml water making the solution 2-5% sucrose enhances palatability.  See also IACUC Policy Additives to Drinking Water
  5. Mucosal irritability:  PI to check tissue compatibility when administering any compounds to mucosal surfaces, i.e. eyes, mouth and trachea.
  6. Osmolarity:Compounds to be administered parenterally must be ~ isoosmolar (280 milli-osmoles/l).  5% Dextrose in Lactated Ringer’s Solution (LRS) which are both iso-osmolar by themselves, may be an exception and can be administered in small amounts SC or IP since the dextrose it is metabolized to CO2 and water rendering the resultant infusion isoosmotic.  However, caution is advised in a dehydrated animal.
  7. Solubility: Some compounds may not be soluble and require administration as a suspension.  Example is sulfamethoxazole-trimethoprim administered in the drinking water.  This suspension must be shaken daily to assure proper dosage.
  8. Light sensitivity: Protect against light exposure either by dispensing in a colored glass or cover clear glass or plastic with foil. Examples include but are not limited to antibiotics such as Septra, cephalexin and sulfatrim.
  9. Toxicity: PI to document (literature search) any new compound or vehicle to be administered to animals in order to determine limitations to use and side effects.

F.   Solvents (vehicle) characteristics

  1. Water: For enteral administration only.  Injectable compounds must be isoosmotic with the possible                                 exception of 50% dextrose.  A small amount of 50% dextrose may be administered IP or IV in a                          hypoglycemic crisis.
  2. Phosphate Buffered Saline (PBS): Whenever possible use sterile normal bufferd saline (PBS) as a solvent.  If the compound to be administered is not soluble in PBS other possible vehicles include:
  3. DMSO (Dimethyl sulfoxide) 0.5% – 5%: An antioxidant, DMSO [(CH3)2SO] is a highly reactive, amphipathic molecule with a highly polar domain and two apolar groups, making it soluble in both aqueous and organic media. Due to its anti-inflammatory properties and the ability to scavenge reactive oxygen particles, DMSO has been used for the treatment of several diseases.  Therapeutic and toxic agents that are not soluble in water are often soluble in DMSO. 7,8
  4. Methylcellulose 2%: is used as a thickener and emulsifier in various food and cosmetic products, and also as a treatment of constipation.  Methylcellulose is a stable sugar with low toxicity and one of the safest and most widely used vehicles available when administered per os.  PO (gavage) or topical   administration appears safe.  Other routes of administration must be scientifically justified.  Characteristics of methylcellulose include its viscosity expressed in centiPoise (cP) and percentage concentration, both of which must be considered when administered to animals.
  5. Corn oil: Gavage administration only.  See tables 1 and 2 for recommended volumes.
  6. Sesame oil: Gavage administration only.  See tables 1 and 2 for recommended volumes.
  7. Ethanol: Ethanol can be lethal if injected IV at high concentration.  Therefore, if an experimental compound has been purified or dissolved in ethanol, it behooves the PI to consider concentration of EtOH, possible dilution if the concentration is high and alternate routes of administration in order to assure animal safety.


  1. The Guide for the Care and Use of Laboratory Animals. NCR.  ILAR.  Eighth Ed. 2011. P.31.
  2. Drug Administration. 444-454.  In Ch. 13.  Biomethodology and Surgical Techniques in The Mouse in Biomedical Research Vol.3.  Second Ed.  2007.  Academic Press.  Fox, J.G. et. al. Eds.
  3. MIT IACUC Policies.
  4. Hawk, C. Terrance Formulary for Laboratory Animals.  Third Ed. 2005.
  5. University of California at San Francisco (UCSF) Retro-orbital Injections in Mice.
  6. Jackson Erica L. Analysis of Lung Tumor Initiation and Progression Using Conditional Expression of Oncogenic K-ras  Genes Dev. 2001, December 15 (24): 3243-3248.
  7. Xing, L and Remick, D.G. Mechanisms of Dimethyl Sulfoxide Augmentation of IL-1β Production.  The Journal of Immunology, 2005, 174:6195-6202.
  8. Brayton, C.F. Dimethyl sulfoxide (DMSO): a review.  Cornell Vet. 1986 Jan: 76(1):61-90.

SC IM IP IV bolus IV infusion Retroorbital* Gavage Intra-cranial Osmotic pump ID Topical
Site Scruff or flank Not recommended Lower right quadrant preferred Lateral tail vein Lateral tail vein Medial canthus Intragast-ric;  See policy Requires surgical placement of cannula See policy Back or flank Probably Back
Volume < 40 ml/kg <0.03-0.05  ml per siteNo more than 2 sites < 40 -80 ml/kg < 5.0 ml/kg 4 ml/kg/hr= 0.1 ml in a 25 g mouse < 200 µl 10-40 ml/kg 0.125-0.25 ml in 25 g mouse ~ 1 μl <0.05 µl/site <25% of total body surface
Needle sizegauge <22-25 < 25-30 <22-25 g <25 g <25 g 27-30 g Gavage needle22-24 g Hamilton syringe or other as approved
Anesthe-sia required No No No No Depends Yes No Depends

Ref. Hawk, C. Terrance Formulary for Laboratory Animals.  Third Ed. 2005.

*     Caution:  If cell lines are administered observe animals regularly to assure a retroorbital mass does not develop.

Volumes administered in rats .

For method please see appropriate section in this policy

SC IM IP IVbolus IV infusion Retroorbital Gavage Intra-cranial Osmotic pump ID Topical
Site Scruff or flank Gluteal or quadriceps musclesNot recommend-ed Lower right quadrant Lateral Tail vein Lateral tail vein Medial canthus Intragast-ric Requires surgical place-ment of cannula Not recommended Probably back or flank
Volume 5-10 ml>5 ml adm. at timed intervals If necessary and approved by IACUC<0.2 mlper site 10-20 ml/kg <5 ml/kg <4 ml/kg/hr1.0 ml/hr ina 250 g rat < 200 ul 10-40  ml/kg μl/hrdepends on site < 25% of total body surface
Needle sizegauge <20 g <25 g <22 g <25 g <25 g <27-39 g Gavage needle22-24 g Hamilton syringe or other as approved
Anesthe-sia required No NoMay make procedure easier No No Depends Yes No Yes/Maybe


BU IACUC Approved April 2011