Development of an in vitro dissolution method using microdialysis sampling technique for implantable drug delivery systems

The major challenge faced during the development of implantable dosage forms for site-specific delivery is monitoring the local concentration of the drug at or around the site of action. The tissue concentration at the site is generally measured by either sacrificing the animal at different points in time or by determining the amount of drug left in the implants at various time intervals. Unfortunately, there are no official in vitro dissolution methods available to study the release characteristics of drugs from this drug delivery system. The objective of this investigation was to develop a simple method using microdialysis sampling technique to serve as an in vitro dissolution method for implantable drug delivery systems. Ciprofloxacin implants were prepared by compressing ciprofloxacin microcapsules in poly(lactic acid) (PLA) and poly(lactic-glycolic acid) (PLGA). A sensitive HPLC method was developed and validated for the assay of Ciprofloxacin. An in vitro dissolution method was developed to study the release characteristics of drug from these implants. The method used a microdialysis sampling technique and a small sample volume of release medium. The various advantages and disadvantages of this method over other USP methods are discussed.