Upon in vivo administration of

a PLGA based injectable depot, water interacts with the polymer and hydrolysis of the ester bonds commences. As the polymer degrades, its hydrophobicity decreases and the number of hydrophilic hydroxyl and carboxylic acid end groups in the matrix increases. An accumulation of hydrophilic acidic end groups has a twofold effect: (1) it increases the amount of water incursion into the polymer and (2) initiates autocatalysis Inhibitors,research,lifescience,medical of the polymer matrix [47]. Therefore, polymer degradation and, consequently, drug release from PLGA is a very complex and dynamic process. This is of particular significance as it provides the researcher a scientifically sound approach to select an appropriate polymer specific

to a therapeutic need or treatment regimen. When plotted as a function of time, drug release from a PLGA matrix occurs in three phases [32]. The first phase of release is known as “initial burst” Inhibitors,research,lifescience,medical and occurs as a result of detachment of surface associated drug or drug that is easily dissociated Inhibitors,research,lifescience,medical from accessible pores in the polymeric microspheres. Depending on the surface area and porosity, a high or low initial burst may be observed. The second phase of release, that is, diffusional release, is a consequence of initial polymer hydration and is followed by “erosional release” or the final phase of drug release. Once the polymer is hydrated, polymer autocatalysis ensues causing bulk hydrolysis, that is, complete polymer degradation and erosion (mass loss). Previous reports have also documented that properties

of the formulation have Inhibitors,research,lifescience,medical an impact on drug release kinetics [48]. Therefore, depending on the properties of the polymer and the microsphere dosage form, the rate and extent of each of these phases can be altered to customize drug release profiles. Hence, in this study, two PLGA copolymers having varying molecular weights and LDN 193189 lactide:glycolide Inhibitors,research,lifescience,medical ratios as well as drug loading were evaluated with an aim to obtain Risperidone PLGA microspheres having varying duration of action. Results and discussions related L-NAME HCl to the findings of the study demonstrate the suitability of this approach in developing sustained release formulations where in vivo behavior can be customized to meet patient needs. 2. Materials and Methods 2.1. Materials Risperidone was purchased from Cipla Ltd., India, and PLGA 50:50 (45 and 74kDa) and 75:25 (54 and 65kDa) from Boehringer Ingelheim (Ingelheim, Germany) and Alkermes (Cambridge, MA). All other chemicals were obtained commercially as analytical grade reagents. 2.2. Preparation of Microspheres The four formulations evaluated were 45kDa PLGA, 50:50 lactide:glycolide (Formulation A), 74kDa PLGA, 50:50 lactide:glycolide (Formulation B), 54kDa PLGA, 75:25 lactide:glycolide (Formulation C), 65kDa PLGA, 75:25 lactide:glycolide (Formulation D).