ALZET^® Technical Tips

 

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 effects

 

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:

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

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 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:

a. 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.

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

c. 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.

d. 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: Priming

 

 

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.

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:

 

 

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:

 

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:

 

 

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:

 

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:

 

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:

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

Download this tip for future reference: Long-Term Administration of Agents in Mice   

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

Download this tip for future reference: Molecular Weight

 

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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Sterility Considerations

 

ALZET pumps are supplied sterile, having been exposed to a sterilizing dose of 60Co. Therefore, we recommend using strict aseptic technique at all times while handling the pumps. If possible, fill the pumps through a 0.22 µM syringe-end filter (e.g.,Millex®-GV). If exterior contamination is suspected during handling, the surface of the pump may be disinfected by wiping it with isopropyl alcohol (70% in water). If this optional step is taken, avoid introducing alcohol solution into the delivery port of the pump. Furthermore, the pump should never be soaked in the alcohol solution. Also, Zephiran® (at any concentration) should never be used to disinfect contaminated pumps. We have found that this topical antiseptic solution remains on the surface of the pump and provokes a serious inflammatory reaction in subcutaneous tissues.

Note: ALZET pumps and flow moderators can not be autoclaved or gas sterilized. Pumps and flow moderators can be re-irradiated with 2.5 Mrad of gamma irradiation from a 60Co source, though this should not be necessary if sterile technique is maintained. This additional sterilization procedure can cause pump discoloration.

The box containing ALZET Osmotic Pumps may be opened to examine the package insert/instructions. Doing so will not compromise pump sterility as the pumps themselves are in sterile, blister packaging.

ALZET pumps are designed to be used upon removal from the packaging, however if unfilled pumps require additional storage prior to the filling or implantation time, it is advised to store the pumps at room temperature in a dry and sterile container, such as a capped conical tube.  Do not refrigerate or freeze ALZET Osmotic Pumps

 

Click here for more information on sterility and the ALZET Osmotic Pumps.

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