ALZET® Technical Tips

Use of the 100 µl ALZET® Micro-Osmotic Pumps With a Catheter

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, and 1002) 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.

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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.

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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

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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

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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., MSDS, published studies, etc.). 

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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

 

Verifying 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

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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

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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

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  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 ul/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 5 months, achieved by serially implanting pumps every 28 days1.

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:

1"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

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Pump Advantages

  • Ensure around-the-clock exposure to test agents at predictable levels
  • Permit continuous administration of short half-life proteins and peptides
  • Provide a convenient method for the chronic dosing of laboratory animals
  • Minimize unwanted experimental variables and ensure reproducible, consistent results
  • Eliminate the need for nighttime or weekend dosing
  • Reduce handling and stress to laboratory animals
  • Small enough for use in mice or very young rats
  • Allow for targeted delivery of agents to virtually any tissue
  • Cost-effective research tool

 

Request a custom bibliography search or select from our list of citations available on-line:

Researchers are saying...

“However formoterol administered intraperitoneally twice a day did not influence LPS-induced premature delivery (data not shown). Osmotic Pumps can maintain the blood concentration of formoterol for over 20h. Thus, it may be of importance that formoterol was continuously and uniformly administered.” (p. 201) Shinkai et al., Reproduction 2003;125:199-203.