ALZET® Technical Tips

Use of the 100 µl Size Pumps with a Catheter or Brain Infusion Kits

1. Using a pair of scissors or pliers, break the white flange from the flow moderator. When removing the flange, be careful not to bend or crush the stainless steel tube.

2. Attach the stainless steel tube to a piece of polyethylene or vinyl catheter tubing with an inside diameter (I.D.) = 0.76 mm (= 0.03 inches). Polyethylene tubing, commonly called PE-60 (I.D. = 0.03 inches), is a good choice for most applications. After attachment, the catheter should cover about 4 mm of the length of the tube.

With the other ALZET models (2000 series and 2ML series), the step of breaking the plastic flange is not necessary since these models have a translucent cap on the flow moderator that can be easily removed to expose a piece of the flow moderator. The reason the 100 µl pump series (1003D, 1007D, 1002, and 1004) were designed without the removable piece was to conserve space and not make them any bigger.

This information can also be located on the included instruction sheet (refer to section VII).  If this sheet is unavailable, it can be downloaded on this page in the "downloads" box to the right.

Download this tip for future reference: 100 µl Catheter

 

The Function of the Flow Moderator

The flow moderator is not a flow regulator and it has no role in determining the pumping rate of an ALZET® Osmotic Pump.   The flow moderator has several important roles:

  • After the pump is filled, the insertion of the flow moderator helps to displace any air trapped within the pump reservoir.  This is essential because all air must be evacuated in order for the pump to function correctly.  
  • More importantly, the flow moderator restricts diffusion of the agent from the exit portal, thereby assuring osmotic control of delivery.  

The flow moderator also acts as an internal splint around which the drug reservoir can be compressed without obstructing outflow.

Download this tip for future reference: Flow Moderator Function

MRI Compatibility

ALZET® Osmotic pumps can be used during MRI procedures by replacing the stainless steel flow moderator with tubing of the same length and outer diameter as the original flow moderator. One such material is PEEK (polyetheretherketone) medical microtubing which has an outer diameter of 0.032 inches and an inner diameter of 0.018 inches and may be purchased from DURECT Corporation.

ALZET Pump Model 1003D, 1007D, 1002, 1004 2001D, 2001, 2002, 2004, 2006 2ML1, 2ML2, 2ML4
PEEK Catalog Numbers 0002612 0002496 0002511

Our PEEK flow moderators are:

  • Sold Sterile
  • Pre-cut according to ALZET pump model
  • Easily inserted by following our complete protocol (see the MRI page)
  • Great Chemical Resistance
  • Biocompatible
  • Sold in packages of 10

In addition, researchers may be interested in obtaining magnetic resonance images of the brain while infusing agents through a brain infusion cannula. When such an experimental procedure is required, a non-metallic brain infusion cannula must be used. Cannula systems compatible with ALZET osmotic pumps and made with non-metallic components, such as plastic, teflon, and fused silica, may be purchased from Plastics One, Inc.

PEEK is a registered trademark of Victrex PLC

Download this tip for future reference: MRI Compatibility

Pulsatile Delivery

The ALZET pumps are miniature infusion devices which are intended to continuously deliver a solution over a given duration.  While it is not possible to start or stop the pump once it is in vivo, you can use a length of external catheter tubing to achieve a variety of delivery methods including the following:

  • Time-patterned delivery of an agent
  • Delivery of solutions which are incompatible with the ALZET pump reservoir
  • Provide a period of no drug delivery for surgical recovery
  • Provide a short period of drug delivery with a longer duration pump

To create this external reservoir, polyethylene tubing should be used because it is thermoformable and can be formed into a permanent coil. The length of tubing depends upon the size and flow rate of the pump being used, and the duration of infusion desired from the solution in the coil. The pump itself is filled with saline, which is separated from the drug solution by a drop of mineral oil or other nonmiscible compound or a bubble of air placed in the tubing at the end between the coil and the pump.

To learn more about catheter use with the ALZET pumps, or to see instructions on how to create a lynch coil, see our catheter use page. 

To view a video demonstrating this lynch coil protocol click here.

See citations using this protocol: Pulsatile References

Download this tip for future reference: Pulsatile Delivery

Cyanoacrylate Adhesive (Application Tip)

Loctite 454 (Item Number: 0008670) is an instant adhesive gel for use with ALZET® Brain Infusion Kits and other brain infusion cannulae. It offers a convenient alternative to cranioplastic dental cements.

The following tips will ensure that you take full advantage of the excellent benefits this adhesive has to offer:

  • Apply a thin layer of adhesive to the underside of the cannula pedestal, so that it coats the pedestal, but not so much that it forms a drop.  Too much adhesive can prolong the drying process and/or result in a weak bond.
  • When lowering the cannula into place, ensure the skull is completely dry to create a proper drying surface.
  • Do not cover the cannula with cyanoacrylate adhesive as you would with dental cement.
  • To remove cyanoacrylate adhesive the following product from Henkel Loctite Corporation can be used:
Product Description Catalog Number
XNMS Solvent (1.75 oz bottle) 76820

Click here to learn more about Loctite 454 or to see supporting documents (e.g., SDS, published studies, etc.). 

Download this tip for future reference: Cyanoacrylate Adhesive (Application Tip)

Verifying Delivery

To verify pump delivery you can perform the following procedures:

  • Measurement of plasma levels during infusion (more information)
  • Measurement of the residual volume in the pump reservoir after explantation (more information)

Note: the weight of a partially empty or discharged pump cannot be used to determine the quantity of drug delivered because the pump imbibes water during operation. Likewise, cutting open a spent pump is not a reliable means of verifying pump performance.

Prior to public release, each lot of ALZET pumps undergoes strict laboratory testing to ensure proper functionality.  This lot specific test data (mean release rate and mean fill volume) can be found on the package insert which comes with the pumps.  The ALZET Osmotic Pump method of operation is very basic and does not easily lend itself to pumping failure.  If the above procedures suggest a non-delivery of your compound, refer to our "Checklist and Tips for Successful Use of ALZET Osmotic Pumps" web page.

To speak with a technical support representative regarding your specific study, call 800-692-2990 or e-mail ALZET Technical Support

Download this tip for future reference: Verifying Delivery

Cannula Placement
Dye Method:

Upon sacrifice, verify the placement of the cannula and its patency as follows:

  1. Fix the brain with a suitable fixative (e.g., 4% formaldehyde).
  2. Remove the jaw and roof of the mouth of the animal and expose the floor of the brain.
  3. Cut the catheter and slowly inject a dye (e.g., Evans Blue) through the catheter toward the cannula.
  4. Expose the tip of the cannula and examine the dye stains to confirm its placement. Alternatively, after the cannula is removed, the brain can be fixed, frozen, and sectioned to confirm cannula placement.

This method can also be found on the Brain Infusion Kit package insert (Section V)
Download package insert

CSF Reflux Method:

Look for reflux of CSF upon insertion of the infusion cannula. This reflux is evident in the majority of successful cannulations.1

Angiotensin II Method for third ventricle verification1

(For use with ALZET compatible acute guide cannulae)

  1. Inject angiotensin II into the infusion cannula of an unanesthetized rat (30 ng in 3 µl of saline).
  2. Monitor for drinking response (>5 ml in 30 minutes)

1 White JD, Schwartz MW. Using osmotic minipumps for intracranial delivery of amino acids and peptides. Methods in Neurosciences, Providing Pharmacological Access to the Brain: Alternate Approaches, T R Flanagan, et al. Academic Press, San Diego 1994; 21:187-200

Download this tip for future reference: Verifying Cannula Placement

Vehicle Viscosity

Researchers often struggle to find an appropriate vehicle that ensures complete solubility of their test agents for animal dosing. Vehicles such as polyethylene glycol (PEG 300, PEG 400), propylene glycol and glycerol offer good solubility alternatives for dissolving lipophyllic compounds, but they are highly viscous. However, viscosity is not a problem for ALZET pump delivery. ALZET Osmotic Pumps are capable of delivering solutions with a viscosity of up to 100,000 cP (1 cP = 1 mPas), this corresponds to roughly 200 times the viscosity of heavy weight engine oil or approximately the viscosity of ketchup!

When using the ALZET Osmotic Pumps with a viscous solution, it is necessary to first prime the pumps in vitro. To prime the pumps, we recommend placing the filled pumps in 37-degree sterile saline for 4-6 hours, preferably overnight. This will allow the pumps to equilibrate and pump at their actual pumping rate prior to implantation. The aforementioned priming duration does not apply for models 2001D and 2004, which take 3 hours and 40 hours respectively to equilibrate. More on priming.

In addition to priming the pumps, it is also important to fill the pumps very slowly in order to minimize the introduction of air bubbles into the pump's reservoir. Researchers will experience a higher degree of backpressure when filling pumps with viscous solutions compared to aqueous solutions. If you encounter a high amount of backpressure, try the following tips:

  • Try filling the pumps with the filling tube at a slight angle relative to the pump (about 15 degrees).   This will create a vent for the air in the reservoir to escape more easily.
  • Insert and remove the flow moderator several times before reinserting the filling tube. This will help expand the orifice. More on filling

To speak with a technical support representative regarding your specific study details, call 800-692-2990 or e-mail us at alzet@durect.com

Download this tip for future reference: Vehicle Viscosity        

Filling Tips

For accurate operation, it is essential that each pump is completely filled with drug solution. Correct filling should be conducted and verified according to the method detailed in the filling section of the ALZET website or in the package insert enclosed in your box of pumps. 

If you experience any difficulty filling the pumps (due to additional backpressure or a highly viscous solution), the following tips can be beneficial:

  • Fill the ALZET pumps with the filling tube at a slight angle (about 15 degrees relative to the pump). This allows the air in the reservoir to escape more easily. 
  • Insert and remove the flow moderator several times before reinserting the filling tube.  This will allow the orifice to slightly expand. 
  • Be sure to use the blunt filling tube provided.  If you need additional filling tubes, they can be ordered here: ALZET® On-Line Ordering
  • Ensure your compound's viscosity is less than 100,000 cP

If you are still having difficulty filling an ALZET pump and would like to speak with a technical support representative, call 800-692-2990 or e-mail us at alzet@durect.com

Download this tip for future reference: Filling Tips

Long-Term Administration of Agents in Mice

ALZET Osmotic Pumps range in duration from 24 hours to 6 weeks. However, mice can be dosed for longer periods by performing serial implantation of pumps. This procedure is generally well tolerated and enables continuous delivery of experimental agents for periods which exceed the duration of a single pump. Chronic delivery of agents to mice is now even easier with the introduction of the new ALZET Model 1004, the smallest pump available for mice. The model 1004 pump delivers continuously for 4 weeks at a rate of 0.11 µl/hr, and can be implanted in mice as small as 10 grams.

The ALZET bibliography contains over 139 published studies reporting the pump replacement procedure to extend duration of drug administration in mice. Currently, the longest duration study reported using ALZET pumps in mice, is 7 months, achieved by serially implanting pumps every 28 days.

The pump replacement procedure is undemanding, requiring only a minor surgical procedure for subcutaneous replacement of pumps in the anesthetized animal. Researchers often use the same location of the spent pump for placing the new pump. If the drug or solvent is known to cause irritation to local tissue, it is recommended to choose a different location for implantation of the new pump in order to allow for proper healing of the original site. The pump replacement procedure is also generally well tolerated by the animal. A number of publications attest to this, as described in the following study quotes:

"The treatment was always very well tolerated without the occurrence of any side effects." Bello L, et al. Clinical Cancer Research 2004; 10(13):4527-4537 5-month duration study with Model 2004 pumps, replaced every 28 days

"All mice that entered the study recovered from the surgical procedure and appeared to have no adverse effects." Feeney SJ, et al. Cytokine 2003; 23(4-5):108-118 13-week duration study with Model 2004, pumps replaced every 4 weeks

"...mice did not show any reaction on the subcutaneously installed ALZET diffusion pumps" Eder IE, et al. Cancer Gene Therapy 2003; 9(2):117-125.; 7-week duration study, pumps replaced every two weeks

Note: Because of their mechanism of operation, ALZET pumps can only be used a single time. Since the reservoir chamber of the pumps cannot be decompressed, or re-inflated once they have compressed to their full capacity, it is NOT physically possible to refill them. In addition, leaving expired pumps in situ is not recommended as these pumps will swell and can leak concentrated salt solutions.

See complete list of mouse long-term administration citations

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Molecular Weight

ALZET Osmotic Pumps can effectively deliver compounds of any molecular size, independently of their physical and chemical properties. Antibodies, hormones, liposomes, and steroids are all examples of high molecular weight compounds, which have successfully been infused using ALZET pumps. To understand why molecular weight is not an issue, it is necessary to understand how the pump works and how its components interact to deliver the drug solution.

The ALZET pumps have three concentric layers. The outer semipermeable membrane allows water to pass into the osmotic layer (sodium chloride). This osmotic layer swells as it gets hydrated, thereby compressing the inner drug chamber housing the drug solution. The drug solution does not pass through a semipermeable membrane, but instead is infused through a hollow metal tube called the flow moderator. The inner diameter of the flow moderator is 500 microns, which is large enough to allow infusion of very large macromolecules commonly used in experimental research.

For more information on how the pump works, see the following webpage: How the Pump Works

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Delivering Multiple Agents

The inner drug chamber of an ALZET Osmotic Pump is not compartmentalized to support the separate loading of multiple agents.  However, you can load and deliver multiple agents when they are combined as a single homogenous solution.  Things to consider when delivering multiple drugs with a single ALZET pump are:

  • Drugs should not have adverse reactions when combined (both within the pump and from a pharmacodynamic perspective). 
  • Drugs should be able to remain soluble, and stable at 37 C for the duration of the infusion.

To deliver multiple agents in an alternating pattern or at predetermined times; see our pulsatile delivery technical tip.  This procedure involves using a catheter as an external reservoir, allowing for the programmed delivery of multiple agents or single agents of varying concentrations.  See more here: Pulsatile Delivery

Download this tip for future reference: Multiple Agents

Priming the ALZET Osmotic Pumps

ALZET pumps have a start-up gradient where the pumps absorb fluid and increase to the in vivo temperature. During this equilibration period, the pumps are slowly building up to their actual release rate as shown in their package insert. Depending on the pump model, this equilibration period can range from 3 hours to 60 hours.  This release rate equilibration will occur automatically in vivo. However, in some experimental cases it may be necessary to equilibrate, or “prime” the pumps in vitro to ensure steady-state delivery after implantation.  Read below to determine if priming of the pumps prior to implantation is required for your study. 

In vitro priming of ALZET pumps is mandatory if:

-Immediate pumping is required after implantation

-A catheter is used with the pump

-A viscous solution is delivered

-The drug solution may have acute toxic effect

If none of the above applies, the in vitro priming step can be skipped. The ALZET pump can be implanted right after filling, and the release rate equilibration will occur automatically in vivo. Please note that steady state delivery of the agent will not be reached until the pump is fully equilibrated (refer to the table below for required priming durations for each pump model). 

Priming durations for ALZET Pumps

Pump Model
Priming Time
1003D
4-6 hours (or overnight)
1007D
4-6 hours (or overnight)
1002
4-6 hours (or overnight)
1004
48 hours
2001D
3 hours
2001
4-6 hours (or overnight)
2002
4-6 hours (or overnight)
2004
40 hours
2006
60 hours
2ML1
4-6 hours (or overnight)
2ML2
4-6 hours (or overnight)
2ML4
4-6 hours (or overnight)

Priming Procedure

1. Fill the pumps in the usual manner; priming is the last step prior to implanting.

2. Place the prefilled pumps in sterile 0.9% saline, PBS or water at 37º C for the specified duration.

3. If using a catheter, it is possible to drape the end of the catheter outside the beaker to avoid any mixing of solutions.

4. Do not be concerned (if due to evaporation), fluid is not observed dripping from the end of the catheter, as evaporative loss can occur. Remove the pump from the saline and implant immediately.

Notes/Tips:

-Immersing the filled pump in an aqueous environment (e.g., conical tube filled with sterile saline) will not result in the priming fluid entering the pump reservoir or the dilution of your compound.  See the function of the flow moderator.

-The pump does not need to be flat, nor fully submerged. 

-If using a catheter, you may observe evaporation at the distal end.  To avoid this, you can prime the pumps without the catheter and attach your filled catheter prior to implantation.  The attachment may introduce a small drop of air; however this won’t affect the functionality of the pump.

-While a small amount of drug solution will be expelled during priming, this will not compromise administration of your compound for the full delivery period. The pumps are manufactured such that the reservoir holds sufficient solution to deliver beyond the specified infusion period.

Download this tip for future reference: Pump Priming

Chemical Compatibility of ALZET Catheters

ALZET Osmotic Pumps can be used with a catheter for various targeted delivery applications. Depending on the research application, researchers can choose among a variety of catheter materials available. The table below contains a list of vehicles/solvents known to be compatible with the inner reservoir material of ALZET pumps. Compatibility of these solvents with ALZET pumps does not imply that they are also compatible with the various catheters available. Refer to the summary table below to confirm catheter compatibility prior to using any of these vehicles, or solvents in your studies. For additional information, please contact ALZET Technical Services (alzet@durect.com; 8006922990)

Chemical Compatibility of Catheter Material
Vehicle / Solvent
Polyurethane†
Silicone‡
Polyethylene
Vinyl

Acids, with pH greater than 1.8

Good

Good

Good

Unknown

Bases, with pH less than 14

Fair

Good

Unknown

Unknown

Cremophor EL, up to 25% in water

Good

Good

Unknown

Unknown

Culture media (1% benzyl alcohol as bacteriostatic)

Good

Good

Good

Good

Cyclodextrins

Good

Good

Good

Good

Dextrose, up to 5%, in water or NaCl

Good

Good

Good

Good

N,N-Dimethyl formamide (DMF), up to 25% in water

Poor

Unknown

Unknown

Poor

DMSO, up to 50% in water or polyethylene glycol

Poor

Good

Good

Poor

DMSO, up to 50% in ethanol (< or =15%) and water

Poor

Good

Good

Poor

Ethanol, up to 15% in water

Poor

Good

Good

Poor

Glycerol

Good*

Good*

Good*

Good*

1-Methyl-2-Pyrrolidone, up to 12.5% in water

Unknown

Unknown

Unknown

Unknown

Phosphate buffer

Good

Good

Good

Good

Polyethylene glycol 300 or 400, neat or in water

Good*

Good*

Good*

Good*

Propylene glycol, neat or in water

Good*

Good*

Good*

Good*

Ringer’s solution

Good

Good

Good

Good

Saline, 0.9% (aqueous salt solution)

Good

Good

Good

Good

Serum (rat, mouse, etc.)

Good

Good

Good

Good

Solutol, up to 30% in water

Unknown

Unknown

Unknown

Unknown

Triacetin, up to 5% in water

Unknown

Unknown

Unknown

Unknown

Tween 80, up to 2%

Good

Good

Unknown

Unknown

Water, distilled

Good

Good

Good

Good

Compatibility Key (Recommendation):

Good: compatible for use with solvent

Poor: should not be used with solvent

Unknown: compatibility testing is suggested prior to use

ALZET polyurethane catheters are made from Dow Pellethane 2363 material

ALZET silicone catheters are made from Dow Silastic material

*Be aware of the viscosity (viscosity may be a problem for catheters with very small inner diameter)

Download this tip for future reference: Catheter Compatibility

Shelf Life of ALZET Osmotic Pumps

The shelf-life for a properly stored ALZET Osmotic Pump is 7 years. That is to say, you can expect consistent and accurate performance for the duration of infusion, provided the pumps were stored in a dry, room temperature environment and were not exposed to direct heat or extreme conditions during the storage period. A lab drawer or cupboard is ideal. ALZET pumps should never be refrigerated or frozen.

Because the shelf-life of ALZET Osmotic Pumps is so long, ordering a large quantity and taking advantage of the volume discount price is suggested. In addition, ordering larger quantities for long-term use allows you to have pumps from the same lot, which may be advantageous if you have an ongoing study.

If you are in possession of ALZET Osmotic Pumps that are older than 7 years, then the pumps can still be used for implantation training purposes or as sham pumps to control for the surgical implantation itself. However, we do not recommend using expired pumps for critical infusion studies since we cannot guarantee its consistent and accurate performance.

In the event that you find it necessary to verify pump functionality, the in vitro testing protocol can be used to determine the ALZET pumping rate.

To learn the manufacturing date of your ALZET Osmotic Pumps, call 800-692-2990 or e-mail ALZET Technical Support. Be sure to locate the lot number of your ALZET pumps (located on the upper left section of your package insert, as shown below)

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In vivo Bioluminescence Imaging Using ALZET® Osmotic Pump


Bioluminescence imaging (BLI) technologies, such as the IVIS® Imaging System from Caliper Life Sciences, allows for real-time monitoring of ongoing biological processes in living animals. BLI is based on the detection of visible light produced during luciferase-mediated oxidation of the molecular substrate, luciferin, when the enzyme is expressed in vivo as a molecular reporter. ALZET pumps provide reliable and prolonged bioluminescent substrate delivery, eliminating complications of repetitive injections and ensuring accurate detection of in vivo bioluminescence.

When using ALZET pumps in BLI studies, the flange on the distal end of the flow moderator can display nearly a 100-fold higher chemi-luminescence signal compared to the background signal. However, pumps using our custom teal or blue flow moderators display no visible chemi-luminescence signal. Thus, for BLI applications researchers should replace the white flow moderators, included in each package of ALZET pumps, with our BLI-compatible flow moderators.

To learn more about BLI-compatible flow moderators, please download our BLI fact sheet here: http://www.alzet.com/resources/documents/BLITechSheet_applications.pdf

To speak with a technical support representative regarding your specific study or to obtain pricing on our colored flow moderators, call 800-692-2990 or e-mail us at alzet@durect.com

Download this tip for future reference: Bioluminescence Imaging

Fluid Around Pump Site

What the fluid is and potential causes:

Following subcutaneous implantation of ALZET Osmotic Pumps, swelling and fluid accumulation around the pump may occur. Provided that infection is ruled out, most likely this swelling is a seroma. A seroma is a pocket of clear, sterile, serous fluid that can accumulate after tissue trauma (i.e., blood vessel damage from tissue dissection). The seroma is a product of tissue inflammation and part of the body's normal defense mechanisms. Another potential cause for damaged blood vessels is low hung feeders in the animal’s cage. If the animal is irritated it can rub against the feeder, causing damaged blood vessels and subsequently a seroma.

Treatment:

These fluids will naturally drain over time provided that there is sufficient circulation, no irritation to the implantation site, and that the animal is in good health. If the swelling does not decrease then there are a couple of options. Draining the site is one option however not recommended as the site may become infected and the swelling may reappear. An alternative method to reduce the swelling is to increase circulation to the healing area. Applying heat from a moist warm towel or from a gauze pack for 10 minutes several times a day will increase blood flow and reabsorb fluid back into the blood stream. In addition, non-steroidal anti-inflammatory medications can be administered to reduce inflammation and/or animal discomfort.*

Prevention:

The best method to treat a seroma is to prevent it from occurring. Determine whether or not the swelling is drug related by comparing the incidence of fluid accumulation between the vehicle control group and the experimental group. Subcutaneous pockets should be created with blunt instruments using a proper blunt dissection technique. Be as gentle as possible when separating the tissue and creating the pocket. When implanting ALZET pumps leave ample space to avoid pressure necrosis, however do not leave excessive dead space, which can stimulate excess fluid.

*For published NSAID dosing information, consult table 6.3 from Flecknell P.A. Laboratory Animal Anaesthesia, second edition; A practical introduction for research workers and technicians.

To speak with a technical support representative regarding seroma causes and management, call 800-692-2990 or e-mail us at alzet@durect.com

Download this tip for future reference: Fluid Around Pump Site

Compatible Vehicle Combinations for Poorly Soluble Compounds


ALZET Osmotic Pumps have proven to be an invaluable tool for delivering test solutions in pre-clinical studies. However, some investigational compounds are poorly soluble and/or are prone to crystallization, which can cause stress to the animal and result in poor pharmacokinetics. Below are select vehicle combinations that are known to be compatible with ALZET pumps and have successfully improved the solubility of poorly soluble test solutions in pre-clinical studies:

Vehicle(s) Concentration (%) Example Research Application

DMSO:PEG

50:50

Isoflavonoids

2-hydroxypropyl-β-Cyclodextrin

45

Hydrophobic compounds

Glycofurol:PEG 300:Cremophor ELP:
Ethanol: Propylene Glycol

25:25:25:15:10

Enzyme inhibitors

The vehicle combinations listed above are compatible with ALZET pumps when used as is. Slight modifications can be considered but should be tested for pump compatibility using the ALZAID Chemical Compatibility Test Kit. ALZAID enables researchers to assess agent and solvent compatibility with ALZET pumps. To learn more about this kit, please visit the following link:
http://www.alzet.com/products/alzaid.html

To view a comprehensive list of commonly used solvents, known to be compatible with ALZET pumps, please visit the following link:
http://www.alzet.com/products/guide_to_use/formulating.html#solvents

Download this tip for future reference: solvents for poorly soluble compounds

Replacing ALZET® Osmotic Pumps for Extended Duration Studies


ALZET pumps range in duration from 24 hours to 6 weeks.  However, laboratory animals can be dosed for periods exceeding the duration of a single pump by serial implantation.  The pump replacement procedure is relatively quick and simple. Refer to the guidelines listed below for more information.

Replacing Subcutaneously Implanted ALZET Pumps

Be sure to follow aseptic technique during the pump replacement procedure to eliminate the risk of infection. Anesthetize the animal using either an inhalable (i.e., Isoflurane) or injectable anesthetic. Make a suitable incision* over the subcutaneous pocket containing the pump. Expose the pump by blunt-dissection using a hemostat. Remove the pump from the subcutaneous pocket. Flush the subcutaneous pocket with warm PBS. Insert the new, properly filled and primed, ALZET pump in the subcutaneous pocket**, delivery portal first. Close the incision with wound clips or sutures.

Replacing Subcutaneously Implanted ALZET Pumps Connected to a Catheter

Via a catheter, ALZET pumps can deliver substances into the venous or arterial circulation, spinal cord, cerebral ventricles, solid brain tissues, or other organs. In chronic drug administration studies involving these applications, only the pumps are replaced to extend delivery while leaving the catheter in place. A suggested procedure is listed below.

Anesthetize the animal using either an inhalable (i.e., Isoflurane) or injectable anesthetic. Make a suitable incision* over the subcutaneous pocket containing the pump. Expose the pump by blunt-dissection using a hemostat. Clamp the catheter approximately 5-10 mm from the tip the pump’s flow moderator (we recommend using a non-serrated micro-serrefine clamp). Using sterile scissors or sharp scalpel, cut the catheter at approximately 1-2 mm from the tip of the flow moderator.  Remove the pump from the subcutaneous pocket. Flush the subcutaneous pocket with warm PBS. Connect the new, properly filled and primed pump to the catheter and insert into the subcutaneous pocket**, delivery portal first. Close the incision with wound clips or sutures.

*The original incision from the initial pump implantation surgery can be used (be sure to remove scar tissue from the edge of the incision for proper wound healing). Alternatively, a new incision, away from the original, can be made.

**The original subcutaneous pocket from the initial pump surgery can be used for subsequent pump replacements (provided the location looks healthy). Alternatively, a new subcutaneous pocket, away from the original, can be made. For multiple pump replacements, some researchers alternate pump placement between two different sites.

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Delayed CNS Delivery


Method For Using Catheter Tubing To Delay Drug Infusion to the CNS

ALZET Osmotic Pumps can be adapted to allow for a recovery period following surgery, such as after implantation of brain cannulae. In this application, the ALZET pump is filled with drug solution and attached to a length of catheter tubing, which has been loaded with a control solution (no drug). If the control solution is such that mixing could occur between it and the drug solution, a spacer substance should be placed between the control and drug solutions. The spacer substance can be any liquid in which the drug solution is not miscible, such as oil or sterile air.

Upon implantation, the ALZET pump begins releasing the drug solution from the pump reservoir into the catheter tubing, displacing control solution from the catheter tubing into the animal. Once all of the control solution is released, the drug solution reaches the end of the catheter tube and is then released into the animal at the pump’s constant rate.

I. Catheter length:

For CNS infusion, the tubing length should be 25% longer than the distance between the pump (placed subcutaneously over the scapulae) and the site of cannula placement.  For example, if this distance is 8 cm, use a 10 cm length of tubing.  If the 10 cm tubing is filled with control solution, the period of time for control solution delivery depends upon the total volume contained in the tubing and the pump model being used.

II. Use the following length-volume conversions to determine the appropriate length of catheter tubing:


Tubing Type


Size


Volume per Centimeter

Vinyl

V3/A*

3.739 µl

Polyethylene (PE)

PE-60*

4.566 µl

PE

PE-50

2.679 µl

*V3/A & PE-60 tubing are available from DURECT Corporation. 
V/3A comes either separately or as part of the ALZET Brain Infusion Kits

III. Example:

A researcher desires a one-week delay following brain cannula implantation. Drug infusion should begin after this delay period and last three weeks. The researcher is using ALZET Model 2004 with the ALZET Brain Infusion Kit, in an adult rat.

ALZET Model 2004 releases at 0.25 µl/hr** and therefore delivers 42 µl over one week. This amount of control solution (i.e., artificial CSF) should be loaded into the tubing.

The vinyl tubing in the brain infusion kit contains 3.739 µl per cm, so 42 µl will fill 11.2 cm. The researcher measures a distance of 8 cm between the pump and cannula implantation sites. The minimum catheter length would be 25% longer than this distance or 10 cm. The 11.2 cm needed to provide the one-week delay will work well. The catheter is filled with aCSF; a small air bubble is introduced to prevent mixing with the drug solution once attached to the primed and filled pump.

Note: When using a catheter, the entire contents of the pump reservoir will not be released in the animal. Some solution will remain in the catheter tubing at the end of the infusion period. Despite this, the pump must be filled completely in order to operate properly

**Nominal pumping rate for Model 2004. (Refer to the instructions inside each box for lot-specific data.)

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Implanting Multiple Pumps


There are many reasons why researchers choose to implant multiple ALZET pumps in a single animal. These reasons include:

  • Administration of multiple compound solutions that cannot be mixed
  • Need for a higher infusion rate than that allowed by a single pump
  • Administration of compounds to multiple targets via catheter
  • Administration of compounds with poor solubility

Implanting more than one ALZET pump is only feasible in animals large enough to accommodate the additional size and weight of multiple pumps. The table below summarizes the minimum animal weight for implantation of two ALZET pumps:

Animal Size* For Implanting Two ALZET Pumps
Pump Model 1003D, 1007D, 1002, 1004 2001D, 2001, 2002, 2004, 2006 2ML1, 2ML2, 2ML4
Subcutaneous 20 g 40 g 300 g
Intraperitoneal 40 g 300 g N/A

* These values are based on the size of animals used in published ALZET pump studies where two pumps were implanted.

The table below contains research citations in which multiple ALZET pumps were used in various animal models:

Animal Pump Model # of Pumps Reference

Mice

1003D

3

P5997    Kuroiwa M, et al. Continuous versus intermittent administration of human endostatin in xenografted human neuroblastoma. J Pediatr Surg 2003; 38(10):1499-1505. "The set of 3 osmotic pumps was retained successfully in the subcutaneous tissue of the treated and control animals throughout the experiment, no decrease in body weight was observed in either group." (p. 1501)

Rat

2002

4

P0432    Khan SR, et al. Experimental induction of crystalluria in rats using mini-osmotic pumps. Urol Res 1983; 11(5):199-205

Dog

2ML1

4

P7118    Gilberto DB, et al. Use of four infusion pumps for postoperative administration of buprenorphine or morphine in dogs. JAVMA 2002; 220(11):1655-1660
Monkey 2ML4 4 P2211    Tarantal AF, et al. Pre and postnatal treatment of the rhesus macaque (Macaca mulatta) with azidothymidine: I. fetal studies. Pediatr Aids HIV Infection: Fetus to Adolescent 1994; 5(1):10-19
Rabbit 2ML1 4 P7178    Cellini C, et al. Effect of epidermal growth factor infusion on fetal rabbit intrauterine growth retardation and small intestinal development. J Pediatr Surg 2004; 39(6):891-897

All surgical procedures, including implanting multiple ALZET pumps, must be approved by the local ethical or legal authority (IACUC, Ethics Committee, Home Office, etc). Visit the following URL to see the minimum animal size estimates for single pump implantations:
http://www.alzet.com/products/guide_to_use/pump_selection.html#table

Contact ALZET Technical Services for a complete list of citations using multiple ALZET pumps in your specific animal model.

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Calculating the Total Duration of Administration for ALZET Osmotic Pumps


The nominal, or theoretical, duration of infusion for ALZET pumps ranges from one day to six weeks depending on the pump model. The actual duration of infusion for all ALZET pumps is always longer than their nominal duration. For example, the Model 2002 pump has a nominal duration of 14 days, but it will always infuse for longer than 2 weeks. The actual duration of administration for a particular lot of pumps can be estimated based on the mean pump rate and fill volumes provided on the instruction sheet included in each box.

      

Lot-specific data for Model 2002 pumps from lot 10196-08

It is important to calculate the actual duration of infusion to:

  • Determine the maximum duration your pump will be able to deliver
  • Estimate the residual volume remaining inside the pumps at any given time point
  • Assess whether prolonged priming of pumps will impact an experiment
  • Determine the actual number of pumps required for long-term studies requiring serial implantation

The actual duration of infusion can be calculated from the following equation:

                                                           D = (V/Q) (0.95)

Where D is duration in hours, V is the Mean Fill Volume in µl, and Q is the Mean Pumping Rate in µl/hr as listed in the lot specifications sheet. The 0.95 or 95% represents the total volume that can be released by a pump. The remaining 5% of the solution is considered dead space and will not be infused.

Using the equation above and the provided lot-specific data, the total duration of infusion for Model 2002 pumps (lot 10196-08) is 387 hours, or 16.1 days. The recommended priming time for Model 2002 pumps is 4-6 hours. Even if these pumps were primed for 48 hours then to total remaining duration of infusion will still be ~14.1 days.

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Bilateral Infusion

Bilateral infusion is a research technique that allows for simultaneous infusion of a test solution into a target area of each brain hemisphere. This method can be used to administer a solution of a test agent simultaneously into brain structures on both hemispheres. This method can also be used to expose one brain hemisphere to a test agent, while infusing the contralateral side with a different test agent or a vehicle control.

ALZET® Osmotic Pumps provide a means for chronic administration of solutions into the brain of awake, unstrained animals. They can be adapted for use in CNS applications requiring bilateral infusion (click here for a list of relevant research citations). One potential way to achieve bilateral infusion is to connect a single ALZET pump to a ‘Y connector”, which diverts the flow of test solution from a single pump into two different outputs. While theoretically feasible, the caveat of using such connector is that even distribution of the solution between the two outputs is not guaranteed. The infusate will likely choose the path of least resistance, leading to uneven dosing at the target areas. To ensure accurate and even bilateral distribution, we recommend implanting two ALZET pumps simultaneously*, with each pump connected to a catheter leading to each target site at the corresponding brain hemisphere. Bilateral cannulae with various lengths and compatible with ALZET pumps are available from Plastics One, Inc.

*Two pumps can be implanted provided the animal is large enough to accommodate the additional pump. Click here for additional information on minimum animal weight requirements for multiple pump implantation.

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