Premature excess release from the Alzet osmotic pump.

This paper alerts investigators to the possibility of an excessive early release from the Alzet osmotic pump. In this research, rats were implanted with 7-day minipumps (model 2001) containing 24 mg/kg/day pyridostigmine, and blood samples were taken at intervals from 5 to 60 min after implantation. All samples showed that blood serum cholinesterase activity was markedly depressed as compared with those of controls. This finding demonstrated that animals were receiving the drug well before the pump's 4- to 6-hr start-up transient period. In a separate study, dye filled pumps were monitored for release when dropped into distilled water at 24 degrees C or 37 degrees C. The pump in the 37 degrees C water released approximately 5% of its contents within 30 sec of submersion, while the pump in the 24 degrees C water released virtually no dye. The early release appears to have been caused by expansion of the pump's contents when the pump, at room temperature, was implanted in the warmer animal.