Dear Raúl Argüello-García, 

The best method to monitor the stability of a drug in a solution contained in an osmotic mini-pump implanted subcutaneously in rats is to monitor blood or plasma levels of the drug administered at several points during the course of administration. This will allow one to detect when such levels reach steady state and whether variables unrelated to pump functionality (e.g., metabolic tolerance) influence experimental results.

In addition, measuring the residual drug solution which remains in the pump reservoir at the time the pump is explanted. To do this, aspirate the solution from the reservoir using a syringe and a filling tube (provided with each box of pumps). To ensure complete recovery, flush the reservoir with additional vehicle. The active

agent in the effluent solution can then be assayed using an appropriate technique. To calculate the average pumping rate, the difference between the amount of drug initially loaded and the residual amount in the reservoir is divided by the elapsed time.

For more on this topic, please use the following link:

http://www.ahmedical.com/ahmedical/pic/2009115658136.pdf

Hoping this will be helpful,

Rafik

Dear Rafik and Anwar,

     Thanks a lot for your valuable advice and information supplied. The mini-pumps have been successfully implanted and work well hence no concern with unexpected blood flushes. We are going to determine the initial and final 7OHDPAT concentrations in the pump solutions and plasma by HPLC.