Sterility: Solutions and Pumps

Because the ALZET pump is designed to contain solutions for as long as six weeks (depending on the model) at 37°C, any microorganisms present in the loading solution may grow, metabolize, and alter the composition of the test solution. This risk is higher if the solution contains materials such as proteins that are potential substrates for microorganisms. For this reason, all solutions loaded into the pumps should be sterile.

Use the following guidelines to minimize interior contamination of the pumps:

• Prepare solutions using sterile laboratory ware.
  
• Prevent particulate contamination during loading of test solutions by using a bacterial filter attached to the filling syringe. Suitable filters are available from Millipore Corporation.
  
• The filling needles supplied with the pump are sterile, and care should be taken not to contaminate them.

Maintaining sterility of solutions

Customers have reported instances in which the biological activity of an agent delivered by the pump seemed to fade or disappear as the experiment progressed. While this observation could be a real and important aspect of the pharmacology of the substance in some cases, in other cases it suggests an inoculation of the test solution with microorganisms.

For example, one laboratory delivered insulin subcutaneously to diabetic dogs using ALZET pumps, changing spent pumps for fresh ones on a weekly basis. Plasma insulin levels always peaked just after a new pump was placed each week, and then faded rapidly. Because the pumps deliver at a constant rate, it was thought that these peculiar results might have been due to bacterial contamination, with degradation of the insulin within the pumps as the infusion time progressed. When we repeated the work, using sterile solutions, insulin levels did not peak and fade, but remained steady.

 

Maintaining pump sterility

ALZET pumps are supplied sterile, having been exposed to a sterilizing dose of ⁶⁰Co. During use, however, exterior contamination from handling may occur. Therefore, we recommend using sterile technique whenever handling the pumps. After loading, the surface of the pump can be cleaned by wiping it with isopropyl alcohol (70% in water). If this optional step is taken, avoid getting alcohol into the delivery port of the pump. The pump should not be soaked in alcohol.

Do not use Zephiran® in any concentration to clean the pumps. We have found that it remains on the surface of the pump and provokes a serious inflammatory reaction in subcutaneous tissues.

Note: Do not autoclave ALZET pumps, flow moderators, or filling tubes. ALZET pumps cannot be gas sterilized either. Pumps and flow moderators can be reirradiated 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 can cause pump discoloration.

top of page