Frequently Asked Questions About ALZET® Osmotic Pumps
- What is the principle of operation of ALZET pumps?
- Do ALZET pumps deliver at a constant rate?
- In what size and type of animal can ALZET pumps be implanted?
- What compounds can be delivered by ALZET pumps?
- Where can ALZET pumps be implanted?
- What drug delivery vehicles are compatible with ALZET pumps?
- How do you implant ALZET pumps?
- Can ALZET pumps be reused?
- What is the shelf life of ALZET pumps?
- What is the delivery duration of ALZET pumps? Will the pumps deliver for longer than the specified duration?
1. What is the principle of operation of ALZET pumps?
ALZET pumps operate by osmotic displacement. An empty reservoir within the core of the pump is filled with the drug or hormone solution to be delivered. Due to the presence of a high concentration of salt in a chamber surrounding the reservoir (but isolated from it by an impermeable layer), water enters the pump through its outer surface (a semipermeable layer). The entry of water increases the volume in the salt chamber, causing compression of the flexible reservoir and delivery of the drug solution into the animal via the exit port.
2. Do ALZET pumps deliver at a constant rate?
Yes, the delivery rate of ALZET pumps is linear. Each batch of pumps is calibrated in our Quality Assurance laboratories. The mean rate of delivery, the accuracy of pumping over time, and pump-to-pump consistency are all measured. The resulting release rate and fill volume (including standard deviations) are provided to you on the instruction sheet in each box of pumps.
3. In what size and type of animal can ALZET pumps be implanted?
ALZET pumps are most commonly used in rodents. The pumps may be implanted in animals other than rodents such as primates, pigs, sheep, rabbits, dogs, chickens, cattle, fish, and cats. In animals which are not homeothermic, the pumping rate of osmotic pumps may be different than the specified rate. Equations are available which allow researchers to calculate the temperature dependent pumping rate at a given body temperature.
Please note: The minimum animal size estimates are based on our experience with male Sprague Dawley rats and Swiss Webster mice. When using the pumps with other strains or genders of rats and mice, or with animals other than rodents, these guidelines should be modified accordingly.
4. What compounds can be delivered by ALZET pumps?
Virtually every compound can be delivered by the pumps, including peptides, hormones, steroids, radioisotopes, chemotherapeutic agents, growth factors, antibiotics, and pharmaceuticals. Molecular weight, physical conformation, and chemical properties do not affect the delivery rate of a given compound. For information about the delivery of a specific compound or class of compounds, please contact ALZET Technical Services by e-mail at alzet@durect.com or by phone at (800) 692-2990 or (408) 367-4036. Additionally, your agent may be listed in our bibliography posted on our web site.
5. Where can ALZET pumps be implanted?
For systemic administration, ALZET pumps can be implanted subcutaneously or intraperitoneally. ALZET pumps can also be attached to a catheter for intravenous, intra-arterial, intraluminal, intragastric, or intracranial administration. Attachment to a catheter does not change the pumping rate of the pumps, nor are any special materials required to connect catheter tubing to the pumps. Refer to Catheter Applications for instructions.
6. What drug delivery vehicles are compatible with ALZET pumps?
The table shown below lists solvents known to be compatible with ALZET pumps. Additional solvents may be compatible, but should be tested before use with the ALZAID Test Kit.
· Acids, with pH greater than 1.8
· Bases, with pH less than 14
· Cremophor EL, up to 25% in water
· Culture media (1% benzyl alcohol as bacteriostatic)
· Dextrose, up to 5%, in water or NaCl
· N,N-Dimethyl formamide (DMF), up to 25% in water
· DMSO, up to 50% in water or polyethylene glycol
· DMSO, up to 50% in ethanol (≤15% ) and water
· Ethanol, up to 15% in water
· Glycerol
· 1-Methyl-2-Pyrrolidone, up to 12.5% in water
· Phosphate buffer
· Polyethylene glycol 300 or 400, neat or in water
· Propylene glycol, neat or in water
· Ringer’s solution (with or without lactate)
· Saline, 0.9% (or other aqueous salt solution)
· Serum (rat, mouse, etc.)
· Solutol, up to 30% in water
· Triacetin, up to 5% in water
· Tween 80, up to 2%
· Water, distilled
Natural oils and organic solvents are NOT compatible with ALZET pumps. Contact with these substances can result in pump malfunction.
7. How do you implant ALZET pumps?
Subcutaneous implantation is a simple surgical procedure which can usually be performed very quickly. For more information on surgical procedures, or for a videotape of surgical techniques, contact ALZET Technical Services by e-mail at alzet@durect.com or by phone at (800) 692-2990 or (408) 367-4036.
8. Can ALZET pumps be re-used?
No, they cannot be reused. Because of their mechanism of operation, ALZET pumps can only be used a single time. The implantation of used pumps as control or sham pumps is not recommended as these pumps will swell and can leak concentrated salt solutions.
9. What is the shelf life of ALZET pumps?
ALZET pumps are have a shelf life of at least 5 to 7 years if stored at room temperature in their original package. Exposure to the following conditions should be avoided:
· Excessive heat (above 120°F)
· Freezing
· Refrigeration (refrigerated environments are moisture-rich)
· Excessive moisture or humidity
10. What is the delivery duration of ALZET pumps? Will the pumps deliver for longer than the specified duration?
The actual duration of an ALZET pump is at least as long as the specified duration／. In many cases it may be 10% to 20% longer than the stated duration due to variations in the reservoir volume and pumping rate of specific lots. To calculate the actual duration perform the following steps:
A. Calculate the usable reservoir volume:
Usable Reservoir Volume = Reservoir Volume x 0.95
B. Calculate the duration of pumping in hours:
Duration (hours) = Usable Reservoir Volume (µl) / Mean Pumping Rate (µl/hr)
C. Convert duration to days:
Duration (days) = Duration (hours) / 24
