I have encountered a problem using 28-day Alzet osmotic pumps, model 2ML4, to administer nicotine in rats. The drug delivery system I am using consists of a piece of coiled polyethylene tubing filled with nicotine solution separated by mineral oil that is attached to the flow moderator of the pump. The length of the coil contains enough drug for 14 days of administration. I implanted these devices into 8 rats for a 28-day period. Prior to implantation, I filled each pump with 2 ml of saline and primed it in 37-degree saline for 24 hours. This same method had previously been used successfully by a former member of my lab.
At the conclusion of the experiment (28 days post-implant), I removed the pumps and tubing and discovered that the majority of the drug contained within the tubing had not been administered. The amount of drug remaining was different for each rat, suggesting that the flow rate was different for each pump. Additionally, I measured the residual volume within the pumps and found that it differed for each pump. I also noted that there was significant tissue buildup around the pump and coil, and both were extremely difficult to remove--I am not sure whether this is typical(?)
I have since set up two pump-and-coil systems in vitro to test the flow rate of the pumps. I primed the pumps exactly as before and attached coiled tubing containing dyed-red saline and oil. At 72 hours one pump appears to be pumping saline at a much faster rate than the other, as evidenced by the fact that the dyed saline has traveled much further down the length of the attached coil. Both pumps were filled with the same amount of saline and are contained in the same beaker of 37-degree saline.
I am wondering if anyone here has experience using Alzet pumps with an attached coil, and if so, have you ever encountered similar problems? What might cause significantly different flow rates between pumps, or cause a pump to stop working before all fluid is expelled? Could this be an issue with the way that the pumps are primed? Any insights that you might have would be greatly appreciated. Thank you
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