IACUC / LARC STANDARD PROCEDURES

Osmotic Pump Implantation in Mice and Rats (Revised August 2008)

General:

Osmotic pumps are miniature, infusion pumps which provide researchers with a safe method for controlled agent delivery in vivo. The pumps function through an osmotic gradient between the pump and the tissue where the pump is implanted. These minipumps can be implanted subcutaneously or intraperitoneally and can also be used for targeted delivery in blood, CSF, brain or other tissues. A single pump may provide up to four weeks of infusion. Details may be found on the Manufacturer website and/or you may contact the IACUC office.

Pumps are to be implanted using aseptic sterile technique and with the animal under general anesthesia:

• Guidelines for Anesthetizing Animals for Research Purpose
• Guidelines for Survival Rodent Surgery
• Pump size should be determined following the manufacturer’s guidelines.
• Pumps and solutions to be infused are to remain sterile
• Analgesia should be provided at the time of implantation, replacement, and/or explant, per the LARC Guidelines For Post-Procedural (Post-Surgical) Analgesia In Research Animals
• The protocol must identify the number of days the pump will be in place. Refer to the manufactures guidelines for this information.
• If there is a need to replace the osmotic pump, justification and details must be provided in the protocol and IACUC approval is required.
• One osmotic pump per animal may be implanted. Your protocol must describe and justify the implantation of two or more pumps.

• Solution to be infused (must be included in the agents section)
• How long the pump will be in place
• If the pump will be replaced, including details regarding explantation and how many times the pump replacements will be conducted.
• If more than one osmotic pump/animal will be implanted
• Size of the pump implanted

Subcutaneous Implantation

The usual site for subcutaneous implantation of osmotic pumps in mice and rats is on the back, slightly posterior to the scapulae. Other regions may be used, provided that the pump does not put pressure on vital organs or impede respiration.

 Subcutaneous Pump Implantation Procedure:

1. Anesthetize the animal. Using aseptic prep and sterile techniques, incise the skin at the site chosen for pump placement.
2. Spread the subcutaneous tissue to create a pocket for the pump. The pocket should be large enough to allow some free movement of the pump (e.g., 1 cm longer than the pump). Avoid making the pocket too large, as this will allow the pump to turn around or slip down on the flank of the animal. The pump should not rest immediately beneath the incision, which could interfere with the healing of the incision.
3. Insert a filled pump into the pocket, delivery portal first. This minimizes interaction between the compound delivered and the healing of the incision.
4. Close the wound with wound clips, sutures or surgical glue. In mice, sutures or surgical glue are recommended for comfort. A larger incision may require sutures or staples for closure of the wound.
5. Provide analgesia as indicated in the approved protocol.

Intraperitoneal Implantation

Osmotic pumps can be implanted intraperitoneally in animals with sufficiently large peritoneal cavities. Allow 24 to 48 hours for the animal to recover after intraperitoneal implantation as normal feeding and weight gain may be disrupted for a day or two, post implantation. For substances which are extensively metabolized by the liver (i.e., have a high “first pass effect”), the intraperitoneal route of administration may produce highly variable concentrations of agent in plasma and consequently highly variable effects. Therefore, the intraperitoneal route should be avoided with agents that have a significant “first-pass effect.”

 Intraperitoneal Pump Implantation Procedure:

1. Anesthetize the animal. Using aseptic prep and sterile technique, make a midline skin incision, 1 cm long, in the lower abdomen under the rib cage.
2. Incise the peritoneal wall directly beneath the cutaneous incision.
3. Insert a filled pump, delivery portal first, into the peritoneal cavity.
4. Close with 4.0 absorbable suture taking care to avoid perforation of the underlying bowel.
5. Close the skin incision with 2 or 3 wound clips, interrupted sutures or surgical glue. In mice, sutures or surgical glue are recommended for comfort. A larger incision may require sutures or staples for closure of the wound.
6. Provide analgesia as indicated in protocol.

Targeted Delivery using an osmotic pump

Osmotic pumps can be used to expose a specific, limited region to a compound. Through a catheter introduced into the arterial blood supply to an organ or affixed within or adjacent to the target tissue, the pump provides continuous and controlled input of a compound. A variety of organs and tissues have become target sites for drug delivery using this method, including: arterial wall, mammary gland, muscle, bladder, nerve, bone, ovary, pericardial space, prostate, eye, ear, stomach, testis, kidney, liver, trachea, lymph node, and uterus. ¹Targeted delivery, including target tissue and surgical access, should be described in detail in the protocol.

Explanting Osmotic Pumps

The purpose for pump removed is:

• To verify delivery by measuring residual volume
• To verify stability & bioactivity of the test agent in solution
• No later than the recommended “explant by” date provided by the manufacturer and listed in the protocol
• To replace it with a new pump in order to continue infusion.

Note: IACUC approval is needed if the pump is to be replaced more than one time. Also, explanted pumps cannot be re-used.

Explantation Procedure – Survival animals

• Once the animal has been anesthetized and the area prepared for aseptic surgery, an incision is made in the skin over the area.
• If the pump has been in place longer than two weeks, or the infusate is an irritant, it may be necessary to free the pump from surrounding connective tissue in order to remove it.

Literature search for SOP refinement:Literature search was performed for refinement of this Standard Procedure on April 24, 2007.

Agents: This procedure requires anesthetics and analgesics.  All agents administered to animals should be listed in the “Agents” section of RIO. Adverse Effects: